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    15. 

  15. 

  16. 

  17. <table class="minipage"><tr><td>Vrije Universiteit Amsterdam
    18. 

  18. <br class="newline" />MPhil Parallel and Distributed Computer Systems
    19. 

  19. <br class="newline" />Compiler Construction Practical</td></tr></table>
    20. 

  20. 

  21. <h2 class="titleHead"><h2 class="titleHead">Piffle<br />
    22. 

  22. A Packet Filter Language</h2></h2>
    23. 

  23. <div class="author" ><div class="author" ><span 
    24. 

  24. class="cmr-17">Jaap Weel</span></div></div>
    25. 

  25. <br />
    26. 

  26. <div class="date" ><div class="date" ><span 
    27. 

  27. class="cmr-17">Version 0.1.2 </span></div></div>
    28. 

  28. 

  29.   </div> </div>
    30. 

  30. 

  31.   <h2 class="likechapterHead"><a 
    32. 

  32.  id="x1-1000"></a>Contents</h2> <div class="tableofcontents">
    33. 

  33.   <span class="chapterToc">1&#x00A0;&#x00A0;<a 
    34. 

  34. href="#x1-20001" id="QQ2-1-2">Notices</a></span>
    35. 

  35. <br />  &#x00A0;<span class="sectionToc">1.1&#x00A0;&#x00A0;<a 
    36. 

  36. href="#x1-30001.1" id="QQ2-1-3">Latest version of this document</a></span>
    37. 

  37. <br />  &#x00A0;<span class="sectionToc">1.2&#x00A0;&#x00A0;<a 
    38. 

  38. href="#x1-40001.2" id="QQ2-1-4">Copyright notice</a></span>
    39. 

  39. <br />  <span class="chapterToc">2&#x00A0;&#x00A0;<a 
    40. 

  40. href="#x1-50002" id="QQ2-1-5">Introduction</a></span>
    41. 

  41. <br />  <span class="chapterToc">3&#x00A0;&#x00A0;<a 
    42. 

  42. href="#x1-60003" id="QQ2-1-6">Bounded packet filters</a></span>
    43. 

  43. <br />  &#x00A0;<span class="sectionToc">3.1&#x00A0;&#x00A0;<a 
    44. 

  44. href="#x1-70003.1" id="QQ2-1-7">Dynamic bounds on packet filters</a></span>
    45. 

  45. <br />  &#x00A0;<span class="sectionToc">3.2&#x00A0;&#x00A0;<a 
    46. 

  46. href="#x1-80003.2" id="QQ2-1-8">Static bounds on arbitrary packet filters</a></span>
    47. 

  47. <br />  &#x00A0;<span class="sectionToc">3.3&#x00A0;&#x00A0;<a 
    48. 

  48. href="#x1-90003.3" id="QQ2-1-9">Proof carrying code</a></span>
    49. 

  49. <br />  &#x00A0;<span class="sectionToc">3.4&#x00A0;&#x00A0;<a 
    50. 

  50. href="#x1-100003.4" id="QQ2-1-10">Bounds on restricted packet filters</a></span>
    51. 

  51. <br />  <span class="chapterToc">4&#x00A0;&#x00A0;<a 
    52. 

  52. href="#x1-110004" id="QQ2-1-11">Language definition</a></span>
    53. 

  53. <br />  &#x00A0;<span class="sectionToc">4.1&#x00A0;&#x00A0;<a 
    54. 

  54. href="#x1-120004.1" id="QQ2-1-12">Vocabulary and representation</a></span>
    55. 

  55. <br />  &#x00A0;<span class="sectionToc">4.2&#x00A0;&#x00A0;<a 
    56. 

  56. href="#x1-130004.2" id="QQ2-1-13">Declarations</a></span>
    57. 

  57. <br />  &#x00A0;<span class="sectionToc">4.3&#x00A0;&#x00A0;<a 
    58. 

  58. href="#x1-140004.3" id="QQ2-1-14">Types</a></span>
    59. 

  59. <br />  &#x00A0;<span class="sectionToc">4.4&#x00A0;&#x00A0;<a 
    60. 

  60. href="#x1-150004.4" id="QQ2-1-15">Expressions</a></span>
    61. 

  61. <br />  &#x00A0;<span class="sectionToc">4.5&#x00A0;&#x00A0;<a 
    62. 

  62. href="#x1-160004.5" id="QQ2-1-16">Operators</a></span>
    63. 

  63. <br />  &#x00A0;<span class="sectionToc">4.6&#x00A0;&#x00A0;<a 
    64. 

  64. href="#x1-170004.6" id="QQ2-1-17">The types of expressions</a></span>
    65. 

  65. <br />  &#x00A0;<span class="sectionToc">4.7&#x00A0;&#x00A0;<a 
    66. 

  66. href="#x1-180004.7" id="QQ2-1-18">Constant expressions</a></span>
    67. 

  67. <br />  &#x00A0;<span class="sectionToc">4.8&#x00A0;&#x00A0;<a 
    68. 

  68. href="#x1-190004.8" id="QQ2-1-19">Source files</a></span>
    69. 

  69. <br />  &#x00A0;<span class="sectionToc">4.9&#x00A0;&#x00A0;<a 
    70. 

  70. href="#x1-200004.9" id="QQ2-1-20">The filter function</a></span>
    71. 

  71. <br />  &#x00A0;<span class="sectionToc">4.10&#x00A0;&#x00A0;<a 
    72. 

  72. href="#x1-210004.10" id="QQ2-1-21">Preprocessor</a></span>
    73. 

  73. <br />  <span class="chapterToc">5&#x00A0;&#x00A0;<a 
    74. 

  74. href="#x1-220005" id="QQ2-1-22">The Piffle compiler, pfc</a></span>
    75. 

  75. <br />  &#x00A0;<span class="sectionToc">5.1&#x00A0;&#x00A0;<a 
    76. 

  76. href="#x1-230005.1" id="QQ2-1-23">The pfc(1) manual page</a></span>
    77. 

  77. <br />  <span class="chapterToc">6&#x00A0;&#x00A0;<a 
    78. 

  78. href="#x1-240006" id="QQ2-1-24">The pcap boilerplate, pcap.c</a></span>
    79. 

  79. <br />  &#x00A0;<span class="sectionToc">6.1&#x00A0;&#x00A0;<a 
    80. 

  80. href="#x1-250006.1" id="QQ2-1-25">The pfc.pcap(1) manual page</a></span>
    81. 

  81. <br />  &#x00A0;<span class="sectionToc">6.2&#x00A0;&#x00A0;<a 
    82. 

  82. href="#x1-260006.2" id="QQ2-1-26">Writing programs for the pcap.c boilerplate</a></span>
    83. 

  83. <br />  <span class="chapterToc">7&#x00A0;&#x00A0;<a 
    84. 

  84. href="#x1-270007" id="QQ2-1-27">The test boilerplate, test.c</a></span>
    85. 

  85. <br />  &#x00A0;<span class="sectionToc">7.1&#x00A0;&#x00A0;<a 
    86. 

  86. href="#x1-280007.1" id="QQ2-1-28">The pfc.test(1) manual page</a></span>
    87. 

  87. <br />  <span class="chapterToc">8&#x00A0;&#x00A0;<a 
    88. 

  88. href="#x1-290008" id="QQ2-1-29">An example of a packet filter</a></span>
    89. 

  89. <br />  &#x00A0;<span class="sectionToc">8.1&#x00A0;&#x00A0;<a 
    90. 

  90. href="#x1-300008.1" id="QQ2-1-30">A packet filter in PFL</a></span>
    91. 

  91. <br />  &#x00A0;<span class="sectionToc">8.2&#x00A0;&#x00A0;<a 
    92. 

  92. href="#x1-310008.2" id="QQ2-1-31">The packet filter translated to C by pfc</a></span>
    93. 

  93.   </div>
    94. 

  94. 

  95.   <h2 class="chapterHead"><span class="titlemark">1</span>.&#x00A0;&#x00A0;<a 
    96. 

  96.  id="x1-20001"></a>Notices</h2>
    97. 

  97.   <h3 class="sectionHead"><span class="titlemark">1.1</span>.&#x00A0;&#x00A0;<a 
    98. 

  98.  id="x1-30001.1"></a>Latest version of this document</h3>
    99. 

  99. <!--l. 23--><p class="noindent">For up-to-date information on Piffle, and the latest version of this document, be sure to visit
    100. 

  100. the following web site:
    101. 

  101. <!--l. 26--><p class="indent">  <span 
    102. 

  102. class="cmti-12">http://code.google.com/p/piffle/wiki/PiffleWiki</span>
    103. 

  103. <!--l. 28--><p class="noindent">
    104. 

  104.   <h3 class="sectionHead"><span class="titlemark">1.2</span>.&#x00A0;&#x00A0;<a 
    105. 

  105.  id="x1-40001.2"></a>Copyright notice</h3>
    106. 

  106. <!--l. 30--><p class="noindent">Copyright (c) 2007, Jaap Weel. This work is licensed under the Creative Commons
    107. 

  107. Attribution&#8211;Share-Alike 3.0 License. To view a copy of this license, visit
    108. 

  108. <!--l. 34--><p class="indent">  <span 
    109. 

  109. class="cmti-12">http://creativecommons.org/licenses/by-sa/3.0/</span>
    110. 

  110. <!--l. 36--><p class="indent">  or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco,
    111. 

  111. California, 94105, USA.
    112. 

  112. 

  113.   <h2 class="chapterHead"><span class="titlemark">2</span>.&#x00A0;&#x00A0;<a 
    114. 

  114.  id="x1-50002"></a>Introduction</h2>
    115. 

  115. <!--l. 44--><p class="noindent">Piffle is a pronounceable form of PFL, that is, Packet Filter Language. (&#8220;Piffle&#8221; is also an
    116. 

  116. obscure word for &#8220;chatter&#8221;.) Piffle is a very simple programming language for writing network
    117. 

  117. packet filters, with one special feature: the compiler can enforce limits on the processor time
    118. 

  118. and memory used for processing each packet of input. This is accomplished by passing
    119. 

  119. arguments to the &#8211;C and &#8211;M command line options. Memory bounds are in words, more or
    120. 

  120. less, and CPU bounds are in arbitrary units.
    121. 

  121. <!--l. 53--><p class="indent">  In this document, I will first consider in general the problem of checking arbitrary programs
    122. 

  122. for transgression of such resource bounds, and notice that it is very hard. I will conclude that
    123. 

  123. in Piffle we must punt and restrict the class of programs that can be used as packet filters,
    124. 

  124. which makes the problem comparatively easy.
    125. 

  125. <!--l. 59--><p class="indent">  After that, I will give the definition of the Piffle language, and some instructions for how to
    126. 

  126. use the Piffle compiler.
    127. 

  127. 

  128.   <h2 class="chapterHead"><span class="titlemark">3</span>.&#x00A0;&#x00A0;<a 
    129. 

  129.  id="x1-60003"></a>Bounded packet filters</h2>
    130. 

  130. <!--l. 65--><p class="noindent">An important requirement in designing network packet processing code is that the amount of
    131. 

  131. time and memory spent processing each packet be bounded. We do not want the entire
    132. 

  132. network connection grinding to a halt because of an unforeseen infinite loop in a packet filter.
    133. 

  133. There are several ways to prevent such havoc. In this chapter, I&#x00A0;will discuss each of them, and
    134. 

  134. explain which one I chose and why.
    135. 

  135.   <h3 class="sectionHead"><span class="titlemark">3.1</span>.&#x00A0;&#x00A0;<a 
    136. 

  136.  id="x1-70003.1"></a>Dynamic bounds on packet filters</h3>
    137. 

  137. <!--l. 74--><p class="noindent">We can check bounds at runtime. For instance, we can run the packet filter on each packet for
    138. 

  138. a specified quota of clock ticks and drop the packet if processing has not finished by the time
    139. 

  139. the quota runs out.
    140. 

  140. <!--l. 79--><p class="indent">  One problem with this runtime approach is that a bug in the packet filters can
    141. 

  141. remain hidden for a long time until some unusual packet is received that triggers the
    142. 

  142. bug.
    143. 

  143. <!--l. 83--><p class="indent">  Another problem is that it is not clear exactly what to do when the bound is exceeded:
    144. 

  144. Should we drop the packet? Should we pass it along unaltered? We would like to be able to
    145. 

  145. give the packet filter author the opportunity to decide what to do with packets that take too
    146. 

  146. long to analyze. But if we allow that sort of flexibility within the dynamic checking framework,
    147. 

  147. we will inevitably have to allow a chunk of cleanup code to deal with &#8220;slow&#8221; packets, which
    148. 

  148. in turn can only run for a restricted amount of time. If <span 
    149. 

  149. class="cmti-12">that </span>time is exceeded, do
    150. 

  150. we need a third program to deal with slow packet filters that have slow cleanup
    151. 

  151. code?
    152. 

  152. <!--l. 94--><p class="noindent">
    153. 

  153.   <h3 class="sectionHead"><span class="titlemark">3.2</span>.&#x00A0;&#x00A0;<a 
    154. 

  154.  id="x1-80003.2"></a>Static bounds on arbitrary packet filters</h3>
    155. 

  155. <!--l. 96--><p class="noindent">Given the problems with checking bounds at run time, we might want to check at compile
    156. 

  156. time. To do that, we need a language in which we can express exactly those packet filter
    157. 

  157. programs that execute within given time and space bounds.
    158. 

  158. <!--l. 101--><p class="indent">  Determining whether a given program runs within these bounds sounds like it ought to be
    159. 

  159. undecidable, but it is not. After all, we are not trying to evaluate whether a given packet filter
    160. 

  160. will terminate <span 
    161. 

  161. class="cmti-12">at all, in the end</span>; we merely want it to terminate within a given number of
    162. 

  162. steps. (The space bound problem is analogous.)
    163. 

  163. <!--l. 107--><p class="indent">  The problem of determining whether a given Turing machine will terminate within a certain
    164. 

  164. number of steps is, in fact, decidable. In a limited number <span 
    165. 

  165. class="cmmi-12">N </span>of steps the machine can read
    166. 

  166. only a limited amount <span 
    167. 

  167. class="cmmi-12">N </span>of its tape, which means we could check whether the time bound by
    168. 

  168. exhaustively running the machine for at most <span 
    169. 

  169. class="cmmi-12">N </span>steps on all tapes of length at most
    170. 

  170. <span 
    171. 

  171. class="cmmi-12">N</span>.
    172. 

  172. <!--l. 114--><p class="indent">  It should be obvious that this procedure, while quite satisfactory as a constructive proof of
    173. 

  173. decidability, is impractical, because the process of bounds checking itself would take lots of
    174. 

  174. time (in fact, exponential in <span 
    175. 

  175. class="cmmi-12">N</span>). What we need is a bound on the process of bounds
    176. 

  176. 

  177. checking.
    178. 

  178. <!--l. 120--><p class="noindent">
    179. 

  179.   <h3 class="sectionHead"><span class="titlemark">3.3</span>.&#x00A0;&#x00A0;<a 
    180. 

  180.  id="x1-90003.3"></a>Proof carrying code</h3>
    181. 

  181. <!--l. 122--><p class="noindent">One way to design a language that would let us check bounds at compile time would be to
    182. 

  182. annotate the program with a proof of the statement that it will terminate within a given
    183. 

  183. number of steps.
    184. 

  184. <!--l. 126--><p class="indent">  Proofs could be provided either as annotations or as part of a type
    185. 

  185. system.<span class="footnote-mark"><a 
    186. 

  186. href="piffle2.html#fn1x5"><sup class="textsuperscript">1</sup></a></span><a 
    187. 

  187.  id="x1-9001f1"></a>
    188. 

  188. The use of proof carrying code would allow all packet filters to be written that can be
    189. 

  189. proven to execute within bounds, and it would allow for the bounds checking problem
    190. 

  190. itself to be tractable. Depending on the details of the formal system used, proof
    191. 

  191. (or type) checking can be polynomial (and often linear) in the length of the proof.
    192. 

  192. Therefore, bound checking of annotated code complies with the rule of thumb that
    193. 

  193. compilers should use only algorithms that are at most polynomial in the length of the
    194. 

  194. program.
    195. 

  195. <!--l. 137--><p class="indent">  The practical liabilities of proof carrying code are well known. Programmers are unfamiliar
    196. 

  196. with proof systems, and those who know their way around them could still have trouble
    197. 

  197. coming up with the (possibly lengthy) proofs in individual cases. Therefore, we
    198. 

  198. will not pursue proof carrying code any further now, and turn instead to a simpler
    199. 

  199. solution.
    200. 

  200. <!--l. 144--><p class="noindent">
    201. 

  201.   <h3 class="sectionHead"><span class="titlemark">3.4</span>.&#x00A0;&#x00A0;<a 
    202. 

  202.  id="x1-100003.4"></a>Bounds on restricted packet filters</h3>
    203. 

  203. <!--l. 146--><p class="noindent">If we do not want to get bogged down in the depths of formal type theory, but still design a
    204. 

  204. language that would let us check bounds at compile time, we arrive at what is, in fact, the
    205. 

  205. traditional solution to the problem of bounded packet filters. We will construct a programming
    206. 

  206. language out of familiar abstractions, and that language will allow us to express a
    207. 

  207. <span 
    208. 

  208. class="cmti-12">large but arbitrary </span>subset of the set of all packet filters that execute in bounded
    209. 

  209. time.
    210. 

  210. <!--l. 154--><p class="indent">  Such a language is not Turing complete, but if it is designed intelligently, it can
    211. 

  211. cover a large fraction of the problems that people may want to solve using packet
    212. 

  212. filters.
    213. 

  213. <!--l. 158--><p class="indent">  An example of a packet filter language based on familiar programming abstractions is the traditional BSD
    214. 

  214. 

  215. packet filter <span 
    216. 

  216. class="cmti-12">bpf</span>.<span class="footnote-mark"><a 
    217. 

  217. href="piffle3.html#fn2x5"><sup class="textsuperscript">2</sup></a></span><a 
    218. 

  218.  id="x1-10001f2"></a>
    219. 

  219. Its packet filters are written in a simple machine code with a little twist: the virtual machine
    220. 

  220. allows jumps forward, but not backward. That way, the time spent executing any given packet
    221. 

  221. filter program is at most proportional to the length of the program.
    222. 

  222. <!--l. 167--><p class="indent">  For Piffle, we take a similar approach. Piffle is not based on machine language, but on block
    223. 

  223. structured, procedural programming languages such as C and Pascal. Just as the <span 
    224. 

  224. class="cmti-12">bpf </span>language
    225. 

  225. omits backward jumps from machine code, Piffle omits unbounded looping constructs and
    226. 

  226. recursive procedure calls from block structured, procedural code. Piffle does provide some
    227. 

  227. bounded looping constructs, and procedure calls are allowed as long as the call graph contains
    228. 

  228. no cycles.
    229. 

  229. 

  230.   <h2 class="chapterHead"><span class="titlemark">4</span>.&#x00A0;&#x00A0;<a 
    231. 

  231.  id="x1-110004"></a>Language definition</h2>
    232. 

  232. <!--l. 193--><p class="noindent">The Piffle language is defined as a set of sentences, called source files, well formed according to
    233. 

  233. the Piffle syntax. To describe the syntax, I will use a modified version of the Backus Normal
    234. 

  234. Form (also known as Backus-Naur Formalism or BNF), using <span 
    235. 

  235. class="cmmi-12">x</span><sup><span 
    236. 

  236. class="cmr-8">?</span></sup> to indicate that <span 
    237. 

  237. class="cmmi-12">x</span>
    238. 

  238. may appear either once or not at all, <span 
    239. 

  239. class="cmmi-12">x</span><sup><span 
    240. 

  240. class="cmr-8">+</span></sup> to indicate that <span 
    241. 

  241. class="cmmi-12">x </span>may appear at least
    242. 

  242. once, and <span 
    243. 

  243. class="cmmi-12">x</span><sup><span 
    244. 

  244. class="cmsy-8">*</span></sup> to indicate that <span 
    245. 

  245. class="cmmi-12">x </span>may appear any number of times, including not at
    246. 

  246. all.
    247. 

  247. <!--l. 201--><p class="indent">  I will not provide a formal definition of the semantics of Piffle. In general, when I do not
    248. 

  248. specify the meaning or type of some Piffle construct, it can be assumed that it is analogous to
    249. 

  249. the semantics of its closest analog in C.
    250. 

  250.   <h3 class="sectionHead"><span class="titlemark">4.1</span>.&#x00A0;&#x00A0;<a 
    251. 

  251.  id="x1-120004.1"></a>Vocabulary and representation</h3>
    252. 

  252. <!--l. 208--><p class="noindent">A well formed Piffle program is composed of tokens, which are identifiers, literals, and reserved
    253. 

  253. tokens. Each token is a sequence of characters, and may not contain whitespace unless this is
    254. 

  254. explicitly specified. Any amount of whitespace may be inserted between tokens, and indeed
    255. 

  255. must be inserted between any two tokens that would make a valid token when put
    256. 

  256. together.
    257. 

  257. <!--l. 215--><p class="indent">  Whitespace is any sequence of blanks, tabs, vertical tabs, form feeds, line feeds, and carriage
    258. 

  258. returns (in C notation, any character in the string <span class="obeylines-h"><span class="verb"><span 
    259. 

  259. class="cmtt-12">"</span><span 
    260. 

  260. class="cmtt-12">&#x00A0;\v\f\t\r\n"</span></span></span>). Comments may also
    261. 

  261. appear wherever whitespace can appear. (Unlike in C, they may <span 
    262. 

  262. class="cmti-12">not </span>appear inside of a token.)
    263. 

  263. In-line comments may be inserted between any two tokens. They are delimited by <span 
    264. 

  264. class="cmtt-12">/* </span>and <span 
    265. 

  265. class="cmtt-12">*/</span>
    266. 

  266. and may be nested. End-of-line comments may also be inserted between any two tokens,
    267. 

  267. and they run from <span 
    268. 

  268. class="cmtt-12">// </span>to the next line end, or the end of the file, whichever comes
    269. 

  269. first.
    270. 

  270. <!--l. 225--><p class="indent">  Identifiers are sequences of letters, digits, and underscores. The first character may not be a
    271. 

  271. digit. <div class="eqnarray">
    272. 

  272.   <center class="math-display" >
    273. 

  273. <img 
    274. 

  274. src="piffle0x.png" alt="                    |--|          |-|        *
    275. 

  275. ident  =   (-letter |-x-)|(letter |-x-|-digit)
    276. 

  276. letter  =   |A || &#x22C5;&#x22C5;&#x22C5; ||Z|| a || &#x22C5;&#x22C5;&#x22C5; | z|
    277. 

  277.            |--|      |--|  ---       ---
    278. 

  278.  digit  =   |0 || &#x22C5;&#x22C5;&#x22C5; ||9|
    279. 

  279.            ---       ---
    280. 

  280. " class="math-display" ></center>
    281. 

  281. </div>
    282. 

  282. <!--l. 235--><p class="indent">  The literals available in Piffle, are numbers, the <span 
    283. 

  283. class="cmtt-12">unit </span>literal, which is the canonical value of
    284. 

  284. type <span 
    285. 

  285. class="cmtt-12">void</span>, <span 
    286. 

  286. class="cmtt-12">true</span>, which means the same as <span 
    287. 

  287. class="cmtt-12">1 :</span><span 
    288. 

  288. class="cmtt-12">&#x00A0;bool</span>, and <span 
    289. 

  289. class="cmtt-12">false</span>, which means the same as <span 
    290. 

  290. class="cmtt-12">0</span>
    291. 

  291. 

  292. <span 
    293. 

  293. class="cmtt-12">:</span><span 
    294. 

  294. class="cmtt-12">&#x00A0;bool</span>. The only numbers available are integers. They can be represented as decimal, octal,
    295. 

  295. or hexidecimal, the same way as in Haskell 98. Note that this differs from C syntax in that
    296. 

  296. leading 0s are simply ignored, and the prefix for octal is 0o or 0O rather than simply
    297. 

  297. 0.
    298. 

  298. <!--l. 253--><p class="indent">  <div class="eqnarray">
    299. 

  299.   <center class="math-display" >
    300. 

  300. <img 
    301. 

  301. src="piffle1x.png" alt="              |----|- |-----|  |------|
    302. 

  302.  literal  =    unit---|-true--|-false---| integer|  |--|
    303. 

  303. integer  =   digit+ | ( 0o|| |0O ) octit+| ( 0x || |0X|) hexit+
    304. 

  304.               |-|      |--|  |-|-      |-|  |-|--  ---|-|
    305. 

  305.   hexit  =    0 || &#x22C5;&#x22C5;&#x22C5; ||9|| A || &#x22C5; &#x22C5;&#x22C5; | F|| a|| &#x22C5;&#x22C5;&#x22C5; | f|
    306. 

  306.               |-|      |--|  ---       ---  ---       ---
    307. 

  307.    octit  =    0--| &#x22C5;&#x22C5;&#x22C5; |-7|
    308. 

  308. " class="math-display" ></center>
    309. 

  309. </div>
    310. 

  310. <!--l. 255--><p class="noindent">
    311. 

  311.   <h3 class="sectionHead"><span class="titlemark">4.2</span>.&#x00A0;&#x00A0;<a 
    312. 

  312.  id="x1-130004.2"></a>Declarations</h3>
    313. 

  313. <!--l. 257--><p class="noindent">Piffle allows no recursion, and all functions must be defined before they are used. Therefore,
    314. 

  314. there is no need for forward declarations. If the return type of a function is omitted, <span 
    315. 

  315. class="cmtt-12">void </span>is
    316. 

  316. implied. The meaning of duplicate definitions is undefined.
    317. 

  317. <!--l. 270--><p class="indent">  <div class="eqnarray">
    318. 

  318.   <center class="math-display" >
    319. 

  319. <img 
    320. 

  320. src="piffle2x.png" alt="declaration   =   vardec | fundec
    321. 

  321.                  |----|      |-|
    322. 

  322.      vardec  =   |var-|ident |:|type  |-|  |-|        |-|
    323. 

  323.     fundec   =   |fun |ident |(|argl? |)| (|:| type )? = |expression
    324. 

  324.                  ----- |-|   --- |-|  --- |-|-        ---
    325. 

  325.        argl  =   ident :--type ( ,--ident -:- type )*
    326. 

  326. " class="math-display" ></center>
    327. 

  327. </div>
    328. 

  328. <!--l. 272--><p class="noindent">
    329. 

  329.   <h3 class="sectionHead"><span class="titlemark">4.3</span>.&#x00A0;&#x00A0;<a 
    330. 

  330.  id="x1-140004.3"></a>Types</h3>
    331. 

  331. <!--l. 274--><p class="noindent">A type in Piffle is <span 
    332. 

  332. class="cmtt-12">void</span>, an atomic type, or an array. Atomic types come in signed and
    333. 

  333. unsigned, and have 8, 16, or 32 bits. Each array type encompasses only arrays of a specific
    334. 

  334. length; you can declare an &#8220;array of 1024 integers&#8221;, but not an &#8220;array of integers&#8221;. This is an
    335. 

  335. important feature, because it is what enables the calculation of resource limits. It is
    336. 

  336. at present <span 
    337. 

  337. class="cmti-12">not </span>actually used for anything else; in particular, there are no bounds
    338. 

  338. checks.
    339. 

  339. <!--l. 290--><p class="indent">  <div class="eqnarray">
    340. 

  340.   <center class="math-display" >
    341. 

  341. <img 
    342. 

  342. src="piffle3x.png" alt="             |-----|                 |--|        |-|
    343. 

  343.   type  =    void---| atomic | atomic-[-|integer ]--
    344. 

  344.              |-----| |---|  |---|  |----|  |--|  |----| |----|
    345. 

  345. atomic   =    bool---|-u8-|| u16-- |-u32-|| s8--| -s16-||-s32-|
    346. 

  346. " class="math-display" ></center>
    347. 

  347. </div>
    348. 

  348. <!--l. 292--><p class="indent">  Whenever a value of type of void is expected, a value of any other type will do as
    349. 

  349. well.
    350. 

  350. <!--l. 295--><p class="noindent">
    351. 

  351. 

  352.   <h3 class="sectionHead"><span class="titlemark">4.4</span>.&#x00A0;&#x00A0;<a 
    353. 

  353.  id="x1-150004.4"></a>Expressions</h3>
    354. 

  354. <!--l. 297--><p class="noindent">Unlike in C or Pascal, in Piffle there is no syntactic distinction between expressions and
    355. 

  355. statements; every expression can be used as a statement and vice versa.
    356. 

  356. <!--l. 327--><p class="indent">  <div class="eqnarray">
    357. 

  357.   <center class="math-display" >
    358. 

  358. <img 
    359. 

  359. src="piffle4x.png" alt="                                                  *
    360. 

  360.  expression   =   expression2  (binop expression2 )  |--|    |-|
    361. 

  361. expression2   =   unop *expression3 ( [--expression -]-) ? ( :-atomic )?
    362. 

  362. 

  363. expression3   =   literal |--|              |-|               |--|
    364. 

  364.               |   ident  (-(-|(expression ( ,--expression) *)?-)-) ?
    365. 

  365.                   |-|           |--|
    366. 

  366.               |   -(-expression -)-|                       ---
    367. 

  367.                   | |              |-| *             |-| * | |
    368. 

  368.               |   |{--(declaration |;--)-( expression  ;--)--}--
    369. 

  369.               |   |if |expression  then  |expression  (|else |expression )?
    370. 

  370.                   |----|      |--|-------      |------|-----        |---|
    371. 

  371.               |   -for-|ident in--expression ( -while--expression) ?-do-|expression
    372. 

  372.                   |----|      |-----|       |---|
    373. 

  373.               |   -for-|ident from---integer -to-|integer
    374. 

  374.                    |-------|           ? |--|
    375. 

  375.                   (-while--|expression )  do--expression
    376. 

  376. " class="math-display" ></center>
    377. 

  377. </div>
    378. 

  378. <!--l. 329--><p class="indent">  Cast expressions (like <span 
    379. 

  379. class="cmtt-12">x : u32</span>) allow the use of a value of one atomic type with another
    380. 

  380. atomic type. The exact meaning of such conversions is undefined but expected to correspond
    381. 

  381. to the behavior of the C compiler on the platform in use.
    382. 

  382. <!--l. 334--><p class="indent">  Blocks have the value of the last expression in them (which is why there is no <span 
    383. 

  383. class="cmtt-12">return</span>
    384. 

  384. statement); if a block contains no expressions, <span 
    385. 

  385. class="cmtt-12">unit </span>is implied.
    386. 

  386. <!--l. 338--><p class="indent">  If-then-else statements have values, and correspond more closely to the C ternary
    387. 

  387. operator (<span 
    388. 

  388. class="cmtt-12">?:</span>) than to the C if-else statement. If an <span 
    389. 

  389. class="cmtt-12">else </span>clause is omitted, <span 
    390. 

  390. class="cmtt-12">unit </span>is
    391. 

  391. implied.
    392. 

  392. <!--l. 342--><p class="indent">  Loops in Piffle are somewhat peculiar, in order to accommodate resource bound checking.
    393. 

  393. There are two types of loops: one will iterate with a variable sequentially bound to each
    394. 

  394. number in a range (which includes both bounds), and the other will iterate with a
    395. 

  395. variable sequentially bound to each element in an array. Both allow the use of a <span 
    396. 

  396. class="cmtt-12">while</span>
    397. 

  397. clause, which will be evaluated before each iteration; if it evaluates to 0, the loop is
    398. 

  398. aborted immediately. The iterator variable is bound within the while clause, so it is
    399. 

  399. perfectly valid to say something like <span 
    400. 

  400. class="cmtt-12">for i from 0 to 10 while is</span><span 
    401. 

  401. class="cmtt-12">_useful(i) do</span>
    402. 

  402. 

  403. <span 
    404. 

  404. class="cmtt-12">...</span>.
    405. 

  405. <!--l. 354--><p class="noindent">
    406. 

  406.   <h3 class="sectionHead"><span class="titlemark">4.5</span>.&#x00A0;&#x00A0;<a 
    407. 

  407.  id="x1-160004.5"></a>Operators</h3>
    408. 

  408. <!--l. 356--><p class="noindent">The operators are given by <div class="eqnarray">
    409. 

  409.   <center class="math-display" >
    410. 

  410. <img 
    411. 

  411. src="piffle5x.png" alt="           |--|  |-|  |-|  |-|  |-|  |---| |---|  |-|
    412. 

  412. binop   =   |*-|| /--| %|-||+-||----|--&#x003C;&#x003C;-||-&#x003E;&#x003E;-|||&#x003C;--
    413. 

  413.         |  |&#x003E; || &#x003C;= || &#x003E;= | ||== |||!= || &amp; || |^|
    414. 

  414.            |--|  |--|  |--|  |--| |---|  |--|  |--|
    415. 

  415.         |  -|-|| &amp;&amp;--| |-|- |-=-||-+=-|| -=--| -*=-
    416. 

  416.            |---|  |--|  |---| |---|  |--|  |----| |----|
    417. 

  417.         |  -%=-|| /=--| -|=-||-&amp;=-|| ^=--| -&#x003E;&#x003E;=-||-&#x003C;&#x003C;=-|
    418. 

  418.            |--|  |-|  |-|  |-|
    419. 

  419. unop   =   -+-|| ---| ~--| !--
    420. 

  420. " class="math-display" ></center>
    421. 

  421. </div>
    422. 

  422. <!--l. 370--><p class="indent">  The grammar as specified so far correctly and completely specifies the language, but it is
    423. 

  423. misleading and ambiguous, because it does not indicate the meaning of certain compound
    424. 

  424. expressions. In fact, the actual Piffle parser will respect the standard C precedence rules, as
    425. 

  425. summarized in the following table.
    426. 

  426.   <div class="tabular"><table class="tabular" 
    427. 

  427. cellspacing="0" cellpadding="0"  
    428. 

  428. ><colgroup id="TBL-2-1g"><col 
    429. 

  429. id="TBL-2-1"><col 
    430. 

  430. id="TBL-2-2"></colgroup><tr 
    431. 

  431. class="hline"><td><hr></td><td><hr></td></tr><tr 
    432. 

  432. class="hline"><td><hr></td><td><hr></td></tr><tr  
    433. 

  433.  style="vertical-align:baseline;" id="TBL-2-1-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-1-1"  
    434. 

  434. class="td11">Operators (ordered from tight to loose)          </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-1-2"  
    435. 

  435. class="td11">Associativity</td>
    436. 

  436. </tr><tr 
    437. 

  437. class="hline"><td><hr></td><td><hr></td></tr><tr  
    438. 

  438.  style="vertical-align:baseline;" id="TBL-2-2-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-2-1"  
    439. 

  439. class="td11"><span class="obeylines-h"><span class="verb"><span 
    440. 

  440. class="cmtt-12">*</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    441. 

  441. class="cmtt-12">/</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    442. 

  442. class="cmtt-12">%</span></span></span>                                 </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-2-2"  
    443. 

  443. class="td11">left-to-right  </td>
    444. 

  444. </tr><tr  
    445. 

  445.  style="vertical-align:baseline;" id="TBL-2-3-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-3-1"  
    446. 

  446. class="td11"><span class="obeylines-h"><span class="verb"><span 
    447. 

  447. class="cmtt-12">+</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    448. 

  448. class="cmtt-12">-</span></span></span>                                    </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-3-2"  
    449. 

  449. class="td11">left-to-right  </td>
    450. 

  450. </tr><tr  
    451. 

  451.  style="vertical-align:baseline;" id="TBL-2-4-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-4-1"  
    452. 

  452. class="td11"><span class="obeylines-h"><span class="verb"><span 
    453. 

  453. class="cmtt-12">&#x003C;&#x003C;</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    454. 

  454. class="cmtt-12">&#x003E;&#x003E;</span></span></span>                                  </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-4-2"  
    455. 

  455. class="td11">left-to-right  </td>
    456. 

  456. </tr><tr  
    457. 

  457.  style="vertical-align:baseline;" id="TBL-2-5-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-5-1"  
    458. 

  458. class="td11"><span class="obeylines-h"><span class="verb"><span 
    459. 

  459. class="cmtt-12">&#x003C;</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    460. 

  460. class="cmtt-12">&#x003E;</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    461. 

  461. class="cmtt-12">&#x003C;=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    462. 

  462. class="cmtt-12">&#x003E;=</span></span></span>                            </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-5-2"  
    463. 

  463. class="td11">left-to-right  </td>
    464. 

  464. </tr><tr  
    465. 

  465.  style="vertical-align:baseline;" id="TBL-2-6-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-6-1"  
    466. 

  466. class="td11"><span class="obeylines-h"><span class="verb"><span 
    467. 

  467. class="cmtt-12">==</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    468. 

  468. class="cmtt-12">!=</span></span></span>                                  </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-6-2"  
    469. 

  469. class="td11">left-to-right  </td>
    470. 

  470. </tr><tr  
    471. 

  471.  style="vertical-align:baseline;" id="TBL-2-7-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-7-1"  
    472. 

  472. class="td11"><span class="obeylines-h"><span class="verb"><span 
    473. 

  473. class="cmtt-12">&amp;</span></span></span>                                      </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-7-2"  
    474. 

  474. class="td11">left-to-right  </td>
    475. 

  475. </tr><tr  
    476. 

  476.  style="vertical-align:baseline;" id="TBL-2-8-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-8-1"  
    477. 

  477. class="td11"><span class="obeylines-h"><span class="verb"><span 
    478. 

  478. class="cmtt-12">^</span></span></span>                                      </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-8-2"  
    479. 

  479. class="td11">left-to-right  </td>
    480. 

  480. </tr><tr  
    481. 

  481.  style="vertical-align:baseline;" id="TBL-2-9-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-9-1"  
    482. 

  482. class="td11"><span class="obeylines-h"><span class="verb"><span 
    483. 

  483. class="cmtt-12">|</span></span></span>                                      </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-9-2"  
    484. 

  484. class="td11">left-to-right  </td>
    485. 

  485. </tr><tr  
    486. 

  486.  style="vertical-align:baseline;" id="TBL-2-10-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-10-1"  
    487. 

  487. class="td11"><span class="obeylines-h"><span class="verb"><span 
    488. 

  488. class="cmtt-12">&amp;&amp;</span></span></span>                                     </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-10-2"  
    489. 

  489. class="td11">left-to-right  </td>
    490. 

  490. </tr><tr  
    491. 

  491.  style="vertical-align:baseline;" id="TBL-2-11-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-11-1"  
    492. 

  492. class="td11"><span class="obeylines-h"><span class="verb"><span 
    493. 

  493. class="cmtt-12">||</span></span></span>                                     </td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-11-2"  
    494. 

  494. class="td11">left-to-right  </td>
    495. 

  495. </tr><tr  
    496. 

  496.  style="vertical-align:baseline;" id="TBL-2-12-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-12-1"  
    497. 

  497. class="td11"><span class="obeylines-h"><span class="verb"><span 
    498. 

  498. class="cmtt-12">=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    499. 

  499. class="cmtt-12">+=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    500. 

  500. class="cmtt-12">-=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    501. 

  501. class="cmtt-12">*=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    502. 

  502. class="cmtt-12">%=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    503. 

  503. class="cmtt-12">/=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    504. 

  504. class="cmtt-12">|=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    505. 

  505. class="cmtt-12">&amp;=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    506. 

  506. class="cmtt-12">^=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    507. 

  507. class="cmtt-12">&#x003E;&#x003E;=</span></span></span>  <span class="obeylines-h"><span class="verb"><span 
    508. 

  508. class="cmtt-12">&#x003C;&#x003C;=</span></span></span></td><td  style="white-space:nowrap; text-align:left;" id="TBL-2-12-2"  
    509. 

  509. class="td11">right-to-left  </td>
    510. 

  510. </tr><tr 
    511. 

  511. class="hline"><td><hr></td><td><hr></td></tr><tr 
    512. 

  512. class="hline"><td><hr></td><td><hr></td></tr><tr  
    513. 

  513.  style="vertical-align:baseline;" id="TBL-2-13-"><td  style="white-space:nowrap; text-align:left;" id="TBL-2-13-1"  
    514. 

  514. class="td11">                                                              </td> </tr></table>
    515. 

  515. 

  516. </div>
    517. 

  517. <!--l. 399--><p class="indent">  The keywords have the loosest possible preference, and thus the expressions at the end of <span 
    518. 

  518. class="cmtt-12">if</span>
    519. 

  519. and <span 
    520. 

  520. class="cmtt-12">for </span>expressions extend to the right as far as possible.
    521. 

  521. <!--l. 403--><p class="indent">  Even though any expression may be used, according to the grammar, as the left-hand side
    522. 

  522. of an assignment, assignment is only a meaningful operation when the left-hand side is an
    523. 

  523. &#8220;lvalue&#8221; of the form  <span 
    524. 

  524. class="cmti-12">ident</span> ( <span class="fbox"><span 
    525. 

  525. class="cmtt-12">[</span></span> <span 
    526. 

  526. class="cmti-12">expression</span> <span class="fbox"><span 
    527. 

  527. class="cmtt-12">]</span></span> ) <sup><span 
    528. 

  528. class="cmr-8">?</span></sup>.
    529. 

  529. <!--l. 408--><p class="noindent">
    530. 

  530.   <h3 class="sectionHead"><span class="titlemark">4.6</span>.&#x00A0;&#x00A0;<a 
    531. 

  531.  id="x1-170004.6"></a>The types of expressions</h3>
    532. 

  532. <!--l. 410--><p class="noindent">The binary operators <span 
    533. 

  533. class="cmtt-12">*</span>, <span 
    534. 

  534. class="cmtt-12">/</span>, <span 
    535. 

  535. class="cmtt-12">%</span>, <span 
    536. 

  536. class="cmtt-12">+</span>, <span 
    537. 

  537. class="cmtt-12">-</span>, <span 
    538. 

  538. class="cmtt-12">&amp;</span>, <span 
    539. 

  539. class="cmtt-12">|</span>, <span 
    540. 

  540. class="cmtt-12">^</span>, <span 
    541. 

  541. class="cmtt-12">=</span>, <span 
    542. 

  542. class="cmtt-12">*=</span>, <span 
    543. 

  543. class="cmtt-12">/=</span>, <span 
    544. 

  544. class="cmtt-12">%=</span>, <span 
    545. 

  545. class="cmtt-12">+=</span>, <span 
    546. 

  546. class="cmtt-12">-=</span>, <span 
    547. 

  547. class="cmtt-12">&amp;=</span>, <span 
    548. 

  548. class="cmtt-12">|=</span>, <span 
    549. 

  549. class="cmtt-12">^=</span>, all take
    550. 

  550. two operands of the same, atomic, type, and return a value of that type, that is,
    551. 

  551. formally,
    552. 

  552.   <center class="math-display" >
    553. 

  553. <img 
    554. 

  554. src="piffle6x.png" alt="*, /,%,+,-,&amp;,| ,^,=,*=,...,^=  : &#x2200;&#x03C4; &#x2208; {bool, u8,u16, u32,s8, s16,s32 }. &#x03C4; &#x00D7; &#x03C4; &#x2192; &#x03C4; .
    555. 

  555. " class="math-display" ></center>
    556. 

  556. <!--l. 420--><p class="nopar"> The unary operators <span 
    557. 

  557. class="cmtt-12">+</span>, <span 
    558. 

  558. class="cmtt-12">-</span>, and <span 
    559. 

  559. class="cmtt-12">~ </span>all take one operand of any integer type and return a value
    560. 

  560. of that type, that is, formally,
    561. 

  561.   <center class="math-display" >
    562. 

  562. <img 
    563. 

  563. src="piffle7x.png" alt="+,- ,~ : &#x2200;&#x03C4; &#x2208; {bool, u8,u16, u32,s8, s16,s32 }. &#x03C4; &#x2192;  &#x03C4; .
    564. 

  564. " class="math-display" ></center>
    565. 

  565. <!--l. 426--><p class="nopar"> The binary operators <span 
    566. 

  566. class="cmtt-12">&#x003C;</span>, <span 
    567. 

  567. class="cmtt-12">&#x003E;</span>, <span 
    568. 

  568. class="cmtt-12">&#x003C;=</span>, <span 
    569. 

  569. class="cmtt-12">&#x003E;=</span>, <span 
    570. 

  570. class="cmtt-12">==</span>, <span 
    571. 

  571. class="cmtt-12">!=</span>, <span 
    572. 

  572. class="cmtt-12">&amp;&amp;</span>, and <span 
    573. 

  573. class="cmtt-12">|| </span>all take two operands of arbitrary
    574. 

  574. atomic types, and return a value of type <span 
    575. 

  575. class="cmtt-12">bool</span>, that is, formally
    576. 

  576.   <center class="math-display" >
    577. 

  577. <img 
    578. 

  578. src="piffle8x.png" alt="&#x003C;, &#x003E;,&#x003C;=,&#x003E;=, ==,!=,&amp;&amp;, || : &#x2200;&#x03C4;,&#x03C5; &#x2208; {bool, u8, u16,u32, s8,s16,s32 }. &#x03C4; &#x00D7; &#x03C5; &#x2192;  bool .
    579. 

  579. " class="math-display" ></center>
    580. 

  580. <!--l. 436--><p class="nopar"> The unary operator <span 
    581. 

  581. class="cmtt-12">! </span>takes one operand of any integer types and returns a value of type
    582. 

  582. <span 
    583. 

  583. class="cmtt-12">bool</span>, that is, formally,
    584. 

  584.   <center class="math-display" >
    585. 

  585. <img 
    586. 

  586. src="piffle9x.png" alt="! : &#x2200;&#x03C4; &#x2208; {bool, u8,u16, u32,s8, s16,s32 }. &#x03C4; &#x2192;  bool .
    587. 

  587. " class="math-display" ></center>
    588. 

    589. 

  589. <!--l. 442--><p class="nopar"> For the binary operators <span 
    590. 

  590. class="cmtt-12">&#x003C;&#x003C;</span>, <span 
    591. 

  591. class="cmtt-12">&#x003E;&#x003E;</span>, <span 
    592. 

  592. class="cmtt-12">&#x003C;&#x003C;=</span>, and <span 
    593. 

  593. class="cmtt-12">&#x003E;&#x003E;=</span>, the value being shifted and the value
    594. 

  594. indicating the number of bits to shift need not be of the same type, but both types
    595. 

  595. must be atomic, and the entire expression gets the type of the value being shifted.
    596. 

  596. Formally,
    597. 

  597.   <center class="math-display" >
    598. 

  598. <img 
    599. 

  599. src="piffle10x.png" alt="&#x003C;&#x003C;,&#x003E;&#x003E;,&#x003C;&#x003C;=, &#x003E;&#x003E;= : &#x2200;&#x03C3;, &#x03C4; &#x2208; {bool, u8,u16,u32, s8,s16, s32}. &#x03C4; &#x00D7; &#x03C3; &#x2192;  &#x03C4; .
    600. 

  600. " class="math-display" ></center>
    601. 

  601. <!--l. 451--><p class="nopar">
    602. 

  602. <!--l. 453--><p class="indent">  A sequence <span 
    603. 

  603. class="cmsy-10x-x-120">{</span><span 
    604. 

  604. class="cmtt-12">...</span><span 
    605. 

  605. class="cmsy-10x-x-120">} </span>of expressions has the value and type of the last expression in the
    606. 

  606. sequence, or <span 
    607. 

  607. class="cmtt-12">void </span>if there are no expressions. All expressions preceding the last are
    608. 

  608. expected to have type <span 
    609. 

  609. class="cmtt-12">void</span>, but as stated above, any other type will do when <span 
    610. 

  610. class="cmtt-12">void </span>is
    611. 

  611. expected.
    612. 

  612. <!--l. 459--><p class="indent">  An <span 
    613. 

  613. class="cmtt-12">if </span>expression consists of a condition, a consequent, and an optional alternative. If the
    614. 

  614. alternative is omitted, <span 
    615. 

  615. class="cmtt-12">unit </span>is implied. The condition may be of any atomic type. The types of
    616. 

  616. the consequent and the alternative must match, but note again that because any type can be
    617. 

  617. used instead of <span 
    618. 

  618. class="cmtt-12">void</span>, if the type of either branch is <span 
    619. 

  619. class="cmtt-12">void</span>, the other branch can have any type.
    620. 

  620. The alternative is evaluated only if the condition evaluates to <span 
    621. 

  621. class="cmtt-12">0</span>; otherwise, the consequent is
    622. 

  622. evaluated. In either case, the entire expression gets the value of the evaluated clause. To
    623. 

  623. clarify:
    624. 

  624. 

  625.   <table 
    626. 

  626. class="verbatim"><tr class="verbatim"><td 
    627. 

  627. class="verbatim"><div class="verbatim">
    628. 

  628. fun&#x00A0;frob&#x00A0;()&#x00A0;:&#x00A0;void&#x00A0;=&#x00A0;{
    629. 

  629. &#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;var&#x00A0;x,&#x00A0;y&#x00A0;:&#x00A0;u32;
    630. 

  630. &#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;if&#x00A0;3&#x00A0;&#x003C;&#x00A0;5&#x00A0;then&#x00A0;do_something();&#x00A0;&#x00A0;/*&#x00A0;do_something()&#x00A0;is&#x00A0;executed&#x00A0;*/
    631. 

  631. &#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;x&#x00A0;=&#x00A0;if&#x00A0;3&#x00A0;&#x003C;&#x00A0;5&#x00A0;then&#x00A0;0&#x00A0;else&#x00A0;1;&#x00A0;&#x00A0;&#x00A0;&#x00A0;/*&#x00A0;x&#x00A0;is&#x00A0;set&#x00A0;to&#x00A0;0&#x00A0;*/
    632. 

  632. &#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;x&#x00A0;=&#x00A0;if&#x00A0;3&#x00A0;&#x003E;&#x00A0;5&#x00A0;then&#x00A0;0&#x00A0;else&#x00A0;1;&#x00A0;&#x00A0;&#x00A0;&#x00A0;/*&#x00A0;x&#x00A0;is&#x00A0;set&#x00A0;to&#x00A0;1&#x00A0;*/
    633. 

  633. &#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;y&#x00A0;=&#x00A0;if&#x00A0;3&#x00A0;&#x003C;&#x00A0;5&#x00A0;then&#x00A0;0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;/*&#x00A0;This&#x00A0;won&#8217;t&#x00A0;type&#x00A0;check!!&#x00A0;*/
    634. 

  634. &#x00A0;<br />};
    635. 

  635. </div>
    636. 

  636. </td></tr></table>
    637. 

  637. <!--l. 476--><p class="nopar">
    638. 

  638. <!--l. 478--><p class="indent">  There are two iteration constructs in Piffle. Both are different from iteration constructs in
    639. 

  639. comparable languages because of the need for computing resource bounds.
    640. 

  640. <!--l. 482--><p class="indent">  An expression of the form
    641. 

  641.   <center class="math-display" >
    642. 

  642. <img 
    643. 

  643. src="piffle11x.png" alt="|---|  |---|   |------|  ? |--|
    644. 

  644. for--&#x03B1; -in-&#x03B2; ( -while--&#x03B3;)  do--&#x03B4;
    645. 

  645. " class="math-display" ></center>
    646. 

  646. <!--l. 483--><p class="nopar"> has type <span 
    647. 

  647. class="cmtt-12">void</span>. The range <span 
    648. 

  648. class="cmmi-12">&#x03B2; </span>must be of type <span 
    649. 

  649. class="cmtt-12">array </span><span 
    650. 

  650. class="cmmi-12">i &#x03C4;</span>, for some integer <span 
    651. 

  651. class="cmmi-12">i </span>and some atomic
    652. 

  652. type <span 
    653. 

  653. class="cmmi-12">&#x03C4;</span>, and the variable <span 
    654. 

  654. class="cmmi-12">&#x03B1; </span>will be of type <span 
    655. 

  655. class="cmmi-12">&#x03C4; </span>and scope over <span 
    656. 

  656. class="cmmi-12">&#x03B3; </span>and <span 
    657. 

  657. class="cmmi-12">&#x03B4;</span>. The condition <span 
    658. 

  658. class="cmmi-12">&#x03B3; </span>may
    659. 

  659. have any atomic type, and the body <span 
    660. 

  660. class="cmmi-12">&#x03B4; </span>must be of type <span 
    661. 

  661. class="cmtt-12">void </span>(with any other type
    662. 

  662. allowed).
    663. 

  663. <!--l. 491--><p class="indent">  An expression of the form
    664. 

  664.   <center class="math-display" >
    665. 

  665. <img 
    666. 

  666. src="piffle12x.png" alt="|----|  |-----|  |---|    |------|  ? |--|
    667. 

  667. -for-|&#x03B1; -from--&#x03B2;0-to-|&#x03B2;1 (-while--&#x03B3;)  -do-&#x03B4;
    668. 

  668. " class="math-display" ></center>
    669. 

  669. <!--l. 492--><p class="nopar"> has type <span 
    670. 

  670. class="cmtt-12">void</span>. The bounds <span 
    671. 

  671. class="cmmi-12">&#x03B2;</span><sub><span 
    672. 

  672. class="cmr-8">0</span><span 
    673. 

  673. class="cmmi-8">,</span><span 
    674. 

  674. class="cmr-8">1</span></sub> must be constant expressions of any atomic type, and <span 
    675. 

  675. class="cmmi-12">&#x03B1; </span>will
    676. 

  676. be of type <span 
    677. 

  677. class="cmtt-12">u32 </span>and scope over <span 
    678. 

  678. class="cmmi-12">&#x03B3; </span>and <span 
    679. 

  679. class="cmmi-12">&#x03B4;</span>. The condition <span 
    680. 

  680. class="cmmi-12">&#x03B3; </span>may have any atomic type, and the
    681. 

  681. body <span 
    682. 

  682. class="cmmi-12">&#x03B4; </span>must be of type <span 
    683. 

  683. class="cmtt-12">void </span>(with any other type allowed).
    684. 

  684. <!--l. 499--><p class="noindent">
    685. 

  685.   <h3 class="sectionHead"><span class="titlemark">4.7</span>.&#x00A0;&#x00A0;<a 
    686. 

  686.  id="x1-180004.7"></a>Constant expressions</h3>
    687. 

  687. <!--l. 501--><p class="noindent">Integer literals are assigned a special type (<span 
    688. 

  688. class="cmtt-12">sliteral</span>) by the compiler. This type is considered
    689. 

  689. atomic, and values of type <span 
    690. 

  690. class="cmtt-12">sliteral </span>can always be used when any atomic type is
    691. 

  691. expected.
    692. 

  692. 

  693. <!--l. 506--><p class="noindent">
    694. 

  694.   <h3 class="sectionHead"><span class="titlemark">4.8</span>.&#x00A0;&#x00A0;<a 
    695. 

  695.  id="x1-190004.8"></a>Source files</h3>
    696. 

  696. <!--l. 508--><p class="noindent">A source file consists of a number of declarations separated by semicolons.
    697. 

  697. <!--l. 513--><p class="indent">  <div class="eqnarray">
    698. 

  698.   <center class="math-display" >
    699. 

  699. <img 
    700. 

  700. src="piffle13x.png" alt="                      |--|
    701. 

  701. file  =   ( declaration |; ) *
    702. 

  702.                       ---
    703. 

  703. " class="math-display" ></center>
    704. 

  704. </div>
    705. 

  705. <!--l. 515--><p class="noindent">
    706. 

  706.   <h3 class="sectionHead"><span class="titlemark">4.9</span>.&#x00A0;&#x00A0;<a 
    707. 

  707.  id="x1-200004.9"></a>The filter function</h3>
    708. 

  708. <!--l. 517--><p class="noindent">The function named <span 
    709. 

  709. class="cmtt-12">filter </span>has a special meaning. It is used as the root of the call graph
    710. 

  710. (which is actually a tree, in the Piffle case) by the compiler when checking for memory
    711. 

  711. and CPU usage bounds. It is also the function that gets called on every incoming
    712. 

  712. packet.
    713. 

  713. <!--l. 522--><p class="indent">  Strictly speaking, this is dependent on which boilerplate is being used. Boilerplates are a
    714. 

  714. concept we will get to in the chapter about the compiler, but rest assured that all
    715. 

  715. currently available boilerplates will cause <span 
    716. 

  716. class="cmtt-12">filter </span>to be called on each incoming
    717. 

  717. packet.
    718. 

  718. <!--l. 529--><p class="noindent">
    719. 

  719.   <h3 class="sectionHead"><span class="titlemark">4.10</span>.&#x00A0;&#x00A0;<a 
    720. 

  720.  id="x1-210004.10"></a>Preprocessor</h3>
    721. 

  721. <!--l. 531--><p class="noindent">It should be possible to run a Piffle program through a regular C preprocessor (cpp). This is
    722. 

  722. not done by default; you would have to do it manually. Also make sure not to use nested
    723. 

  723. comments if you want to use cpp. The compiler does not interpret cpp line directives, so any
    724. 

  724. error messages you get about preprocessed code will refer to positions in the preprocessed
    725. 

  725. source.
    726. 

  726. 

  727. 

  728.   <h2 class="chapterHead"><span class="titlemark">5</span>.&#x00A0;&#x00A0;<a 
    729. 

  729.  id="x1-220005"></a>The Piffle compiler, pfc</h2>
    730. 

  730. <!--l. 540--><p class="noindent">The Piffle compiler, pfc, is a fairly simple compiler, written in the Haskell programming language,
    731. 

  731. that outputs C code. It is documented in the pfc(1) man page, which is reproduced here in its
    732. 

  732. entirety.<span class="footnote-mark"><a 
    733. 

  733. href="piffle4.html#fn1x7"><sup class="textsuperscript">1</sup></a></span><a 
    734. 

  734.  id="x1-22001f1"></a>
    735. 

  735.   <h3 class="sectionHead"><span class="titlemark">5.1</span>.&#x00A0;&#x00A0;<a 
    736. 

  736.  id="x1-230005.1"></a>The pfc(1) manual page</h3>
    737. 

  737. <!--l. 550--><p class="noindent">
    738. 

  738.   <div class="fancyvrb" id="fancyvrb1">
    739. 

  739. <a 
    740. 

  740.  id="x1-23002r1"></a><span 
    741. 

  741. class="cmtt-10">&#x00A0;</span><span 
    742. 

  742. class="cmtt-10">&#x00A0;PFC(1)</span><span 
    743. 

  743. class="cmtt-10">&#x00A0;</span><span 
    744. 

  744. class="cmtt-10">&#x00A0;</span><span 
    745. 

  745. class="cmtt-10">&#x00A0;</span><span 
    746. 

  746. class="cmtt-10">&#x00A0;</span><span 
    747. 

  747. class="cmtt-10">&#x00A0;</span><span 
    748. 

  748. class="cmtt-10">&#x00A0;</span><span 
    749. 

  749. class="cmtt-10">&#x00A0;</span><span 
    750. 

  750. class="cmtt-10">&#x00A0;</span><span 
    751. 

  751. class="cmtt-10">&#x00A0;</span><span 
    752. 

  752. class="cmtt-10">&#x00A0;</span><span 
    753. 

  753. class="cmtt-10">&#x00A0;</span><span 
    754. 

  754. class="cmtt-10">&#x00A0;</span><span 
    755. 

  755. class="cmtt-10">&#x00A0;</span><span 
    756. 

  756. class="cmtt-10">&#x00A0;</span><span 
    757. 

  757. class="cmtt-10">&#x00A0;</span><span 
    758. 

  758. class="cmtt-10">&#x00A0;</span><span 
    759. 

  759. class="cmtt-10">&#x00A0;</span><span 
    760. 

  760. class="cmtt-10">&#x00A0;</span><span 
    761. 

  761. class="cmtt-10">&#x00A0;</span><span 
    762. 

  762. class="cmtt-10">&#x00A0;</span><span 
    763. 

  763. class="cmtt-10">&#x00A0;</span><span 
    764. 

  764. class="cmtt-10">&#x00A0;</span><span 
    765. 

  765. class="cmtt-10">&#x00A0;</span><span 
    766. 

  766. class="cmtt-10">&#x00A0;</span><span 
    767. 

  767. class="cmtt-10">&#x00A0;</span><span 
    768. 

  768. class="cmtt-10">&#x00A0;</span><span 
    769. 

  769. class="cmtt-10">&#x00A0;</span><span 
    770. 

  770. class="cmtt-10">&#x00A0;</span><span 
    771. 

  771. class="cmtt-10">&#x00A0;</span><span 
    772. 

  772. class="cmtt-10">&#x00A0;</span><span 
    773. 

  773. class="cmtt-10">&#x00A0;</span><span 
    774. 

  774. class="cmtt-10">&#x00A0;</span><span 
    775. 

  775. class="cmtt-10">&#x00A0;</span><span 
    776. 

  776. class="cmtt-10">&#x00A0;</span><span 
    777. 

  777. class="cmtt-10">&#x00A0;</span><span 
    778. 

  778. class="cmtt-10">&#x00A0;</span><span 
    779. 

  779. class="cmtt-10">&#x00A0;</span><span 
    780. 

  780. class="cmtt-10">&#x00A0;</span><span 
    781. 

  781. class="cmtt-10">&#x00A0;</span><span 
    782. 

  782. class="cmtt-10">&#x00A0;</span><span 
    783. 

  783. class="cmtt-10">&#x00A0;</span><span 
    784. 

  784. class="cmtt-10">&#x00A0;</span><span 
    785. 

  785. class="cmtt-10">&#x00A0;</span><span 
    786. 

  786. class="cmtt-10">&#x00A0;</span><span 
    787. 

  787. class="cmtt-10">&#x00A0;</span><span 
    788. 

  788. class="cmtt-10">&#x00A0;</span><span 
    789. 

  789. class="cmtt-10">&#x00A0;</span><span 
    790. 

  790. class="cmtt-10">&#x00A0;</span><span 
    791. 

  791. class="cmtt-10">&#x00A0;</span><span 
    792. 

  792. class="cmtt-10">&#x00A0;</span><span 
    793. 

  793. class="cmtt-10">&#x00A0;</span><span 
    794. 

  794. class="cmtt-10">&#x00A0;</span><span 
    795. 

  795. class="cmtt-10">&#x00A0;</span><span 
    796. 

  796. class="cmtt-10">&#x00A0;</span><span 
    797. 

  797. class="cmtt-10">&#x00A0;</span><span 
    798. 

  798. class="cmtt-10">&#x00A0;</span><span 
    799. 

  799. class="cmtt-10">&#x00A0;</span><span 
    800. 

  800. class="cmtt-10">&#x00A0;</span><span 
    801. 

  801. class="cmtt-10">&#x00A0;</span><span 
    802. 

  802. class="cmtt-10">&#x00A0;</span><span 
    803. 

  803. class="cmtt-10">&#x00A0;</span><span 
    804. 

  804. class="cmtt-10">&#x00A0;</span><span 
    805. 

  805. class="cmtt-10">&#x00A0;</span><span 
    806. 

  806. class="cmtt-10">&#x00A0;</span><span 
    807. 

  807. class="cmtt-10">&#x00A0;</span><span 
    808. 

  808. class="cmtt-10">&#x00A0;PFC(1)</span>
    809. 

  809. <br class="fancyvrb" /><a 
    810. 

  810.  id="x1-23004r2"></a><span 
    811. 

  811. class="cmtt-10">&#x00A0;</span><span 
    812. 

  812. class="cmtt-10">&#x00A0;</span>
    813. 

  813. <br class="fancyvrb" /><a 
    814. 

  814.  id="x1-23006r3"></a><span 
    815. 

  815. class="cmtt-10">&#x00A0;</span><span 
    816. 

  816. class="cmtt-10">&#x00A0;</span>
    817. 

  817. <br class="fancyvrb" /><a 
    818. 

  818.  id="x1-23008r4"></a><span 
    819. 

  819. class="cmtt-10">&#x00A0;</span><span 
    820. 

  820. class="cmtt-10">&#x00A0;</span>
    821. 

  821. <br class="fancyvrb" /><a 
    822. 

  822.  id="x1-23010r5"></a><span 
    823. 

  823. class="cmtt-10">&#x00A0;</span><span 
    824. 

  824. class="cmtt-10">&#x00A0;NAME</span>
    825. 

  825. <br class="fancyvrb" /><a 
    826. 

  826.  id="x1-23012r6"></a><span 
    827. 

  827. class="cmtt-10">&#x00A0;</span><span 
    828. 

  828. class="cmtt-10">&#x00A0;</span><span 
    829. 

  829. class="cmtt-10">&#x00A0;</span><span 
    830. 

  830. class="cmtt-10">&#x00A0;</span><span 
    831. 

  831. class="cmtt-10">&#x00A0;</span><span 
    832. 

  832. class="cmtt-10">&#x00A0;</span><span 
    833. 

  833. class="cmtt-10">&#x00A0;</span><span 
    834. 

  834. class="cmtt-10">&#x00A0;</span><span 
    835. 

  835. class="cmtt-10">&#x00A0;pfc</span><span 
    836. 

  836. class="cmtt-10">&#x00A0;-</span><span 
    837. 

  837. class="cmtt-10">&#x00A0;Piffle</span><span 
    838. 

  838. class="cmtt-10">&#x00A0;Compiler</span>
    839. 

  839. <br class="fancyvrb" /><a 
    840. 

  840.  id="x1-23014r7"></a><span 
    841. 

  841. class="cmtt-10">&#x00A0;</span><span 
    842. 

  842. class="cmtt-10">&#x00A0;</span>
    843. 

  843. <br class="fancyvrb" /><a 
    844. 

  844.  id="x1-23016r8"></a><span 
    845. 

  845. class="cmtt-10">&#x00A0;</span><span 
    846. 

  846. class="cmtt-10">&#x00A0;SYNOPSIS</span>
    847. 

  847. <br class="fancyvrb" /><a 
    848. 

  848.  id="x1-23018r9"></a><span 
    849. 

  849. class="cmtt-10">&#x00A0;</span><span 
    850. 

  850. class="cmtt-10">&#x00A0;</span><span 
    851. 

  851. class="cmtt-10">&#x00A0;</span><span 
    852. 

  852. class="cmtt-10">&#x00A0;</span><span 
    853. 

  853. class="cmtt-10">&#x00A0;</span><span 
    854. 

  854. class="cmtt-10">&#x00A0;</span><span 
    855. 

  855. class="cmtt-10">&#x00A0;</span><span 
    856. 

  856. class="cmtt-10">&#x00A0;</span><span 
    857. 

  857. class="cmtt-10">&#x00A0;pfc</span><span 
    858. 

  858. class="cmtt-10">&#x00A0;[OPTIONS]</span><span 
    859. 

  859. class="cmtt-10">&#x00A0;file.pfl</span>
    860. 

  860. <br class="fancyvrb" /><a 
    861. 

  861.  id="x1-23020r10"></a><span 
    862. 

  862. class="cmtt-10">&#x00A0;</span><span 
    863. 

  863. class="cmtt-10">&#x00A0;</span>
    864. 

  864. <br class="fancyvrb" /><a 
    865. 

  865.  id="x1-23022r11"></a><span 
    866. 

  866. class="cmtt-10">&#x00A0;</span><span 
    867. 

  867. class="cmtt-10">&#x00A0;INTRODUCTION</span>
    868. 

  868. <br class="fancyvrb" /><a 
    869. 

  869.  id="x1-23024r12"></a><span 
    870. 

  870. class="cmtt-10">&#x00A0;</span><span 
    871. 

  871. class="cmtt-10">&#x00A0;</span><span 
    872. 

  872. class="cmtt-10">&#x00A0;</span><span 
    873. 

  873. class="cmtt-10">&#x00A0;</span><span 
    874. 

  874. class="cmtt-10">&#x00A0;</span><span 
    875. 

  875. class="cmtt-10">&#x00A0;</span><span 
    876. 

  876. class="cmtt-10">&#x00A0;</span><span 
    877. 

  877. class="cmtt-10">&#x00A0;</span><span 
    878. 

  878. class="cmtt-10">&#x00A0;Piffle</span><span 
    879. 

  879. class="cmtt-10">&#x00A0;is</span><span 
    880. 

  880. class="cmtt-10">&#x00A0;a</span><span 
    881. 

  881. class="cmtt-10">&#x00A0;pronounceable</span><span 
    882. 

  882. class="cmtt-10">&#x00A0;form</span><span 
    883. 

  883. class="cmtt-10">&#x00A0;of</span><span 
    884. 

  884. class="cmtt-10">&#x00A0;PFL,</span><span 
    885. 

  885. class="cmtt-10">&#x00A0;that</span><span 
    886. 

  886. class="cmtt-10">&#x00A0;is,</span><span 
    887. 

  887. class="cmtt-10">&#x00A0;Packet</span><span 
    888. 

  888. class="cmtt-10">&#x00A0;Filter</span><span 
    889. 

  889. class="cmtt-10">&#x00A0;Language.</span>
    890. 

  890. <br class="fancyvrb" /><a 
    891. 

  891.  id="x1-23026r13"></a><span 
    892. 

  892. class="cmtt-10">&#x00A0;</span><span 
    893. 

  893. class="cmtt-10">&#x00A0;</span><span 
    894. 

  894. class="cmtt-10">&#x00A0;</span><span 
    895. 

  895. class="cmtt-10">&#x00A0;</span><span 
    896. 

  896. class="cmtt-10">&#x00A0;</span><span 
    897. 

  897. class="cmtt-10">&#x00A0;</span><span 
    898. 

  898. class="cmtt-10">&#x00A0;</span><span 
    899. 

  899. class="cmtt-10">&#x00A0;</span><span 
    900. 

  900. class="cmtt-10">&#x00A0;Piffle</span><span 
    901. 

  901. class="cmtt-10">&#x00A0;is</span><span 
    902. 

  902. class="cmtt-10">&#x00A0;a</span><span 
    903. 

  903. class="cmtt-10">&#x00A0;very</span><span 
    904. 

  904. class="cmtt-10">&#x00A0;simple</span><span 
    905. 

  905. class="cmtt-10">&#x00A0;programming</span><span 
    906. 

  906. class="cmtt-10">&#x00A0;language</span><span 
    907. 

  907. class="cmtt-10">&#x00A0;for</span><span 
    908. 

  908. class="cmtt-10">&#x00A0;writing</span><span 
    909. 

  909. class="cmtt-10">&#x00A0;network</span><span 
    910. 

  910. class="cmtt-10">&#x00A0;packet</span>
    911. 

  911. <br class="fancyvrb" /><a 
    912. 

  912.  id="x1-23028r14"></a><span 
    913. 

  913. class="cmtt-10">&#x00A0;</span><span 
    914. 

  914. class="cmtt-10">&#x00A0;</span><span 
    915. 

  915. class="cmtt-10">&#x00A0;</span><span 
    916. 

  916. class="cmtt-10">&#x00A0;</span><span 
    917. 

  917. class="cmtt-10">&#x00A0;</span><span 
    918. 

  918. class="cmtt-10">&#x00A0;</span><span 
    919. 

  919. class="cmtt-10">&#x00A0;</span><span 
    920. 

  920. class="cmtt-10">&#x00A0;</span><span 
    921. 

  921. class="cmtt-10">&#x00A0;filters,</span><span 
    922. 

  922. class="cmtt-10">&#x00A0;</span><span 
    923. 

  923. class="cmtt-10">&#x00A0;with</span><span 
    924. 

  924. class="cmtt-10">&#x00A0;</span><span 
    925. 

  925. class="cmtt-10">&#x00A0;one</span><span 
    926. 

  926. class="cmtt-10">&#x00A0;special</span><span 
    927. 

  927. class="cmtt-10">&#x00A0;feature:</span><span 
    928. 

  928. class="cmtt-10">&#x00A0;the</span><span 
    929. 

  929. class="cmtt-10">&#x00A0;compiler</span><span 
    930. 

  930. class="cmtt-10">&#x00A0;can</span><span 
    931. 

  931. class="cmtt-10">&#x00A0;enforce</span><span 
    932. 

  932. class="cmtt-10">&#x00A0;limits</span><span 
    933. 

  933. class="cmtt-10">&#x00A0;on</span>
    934. 

  934. <br class="fancyvrb" /><a 
    935. 

  935.  id="x1-23030r15"></a><span 
    936. 

  936. class="cmtt-10">&#x00A0;</span><span 
    937. 

  937. class="cmtt-10">&#x00A0;</span><span 
    938. 

  938. class="cmtt-10">&#x00A0;</span><span 
    939. 

  939. class="cmtt-10">&#x00A0;</span><span 
    940. 

  940. class="cmtt-10">&#x00A0;</span><span 
    941. 

  941. class="cmtt-10">&#x00A0;</span><span 
    942. 

  942. class="cmtt-10">&#x00A0;</span><span 
    943. 

  943. class="cmtt-10">&#x00A0;</span><span 
    944. 

  944. class="cmtt-10">&#x00A0;the</span><span 
    945. 

  945. class="cmtt-10">&#x00A0;processor</span><span 
    946. 

  946. class="cmtt-10">&#x00A0;time</span><span 
    947. 

  947. class="cmtt-10">&#x00A0;and</span><span 
    948. 

  948. class="cmtt-10">&#x00A0;memory</span><span 
    949. 

  949. class="cmtt-10">&#x00A0;used</span><span 
    950. 

  950. class="cmtt-10">&#x00A0;for</span><span 
    951. 

  951. class="cmtt-10">&#x00A0;processing</span><span 
    952. 

  952. class="cmtt-10">&#x00A0;each</span><span 
    953. 

  953. class="cmtt-10">&#x00A0;packet</span><span 
    954. 

  954. class="cmtt-10">&#x00A0;of</span><span 
    955. 

  955. class="cmtt-10">&#x00A0;input.</span>
    956. 

  956. <br class="fancyvrb" /><a 
    957. 

  957.  id="x1-23032r16"></a><span 
    958. 

  958. class="cmtt-10">&#x00A0;</span><span 
    959. 

  959. class="cmtt-10">&#x00A0;</span><span 
    960. 

  960. class="cmtt-10">&#x00A0;</span><span 
    961. 

  961. class="cmtt-10">&#x00A0;</span><span 
    962. 

  962. class="cmtt-10">&#x00A0;</span><span 
    963. 

  963. class="cmtt-10">&#x00A0;</span><span 
    964. 

  964. class="cmtt-10">&#x00A0;</span><span 
    965. 

  965. class="cmtt-10">&#x00A0;</span><span 
    966. 

  966. class="cmtt-10">&#x00A0;This</span><span 
    967. 

  967. class="cmtt-10">&#x00A0;is</span><span 
    968. 

  968. class="cmtt-10">&#x00A0;accomplished</span><span 
    969. 

  969. class="cmtt-10">&#x00A0;by</span><span 
    970. 

  970. class="cmtt-10">&#x00A0;passing</span><span 
    971. 

  971. class="cmtt-10">&#x00A0;arguments</span><span 
    972. 

  972. class="cmtt-10">&#x00A0;to</span><span 
    973. 

  973. class="cmtt-10">&#x00A0;the</span><span 
    974. 

  974. class="cmtt-10">&#x00A0;-C</span><span 
    975. 

  975. class="cmtt-10">&#x00A0;and</span><span 
    976. 

  976. class="cmtt-10">&#x00A0;-M</span><span 
    977. 

  977. class="cmtt-10">&#x00A0;command</span><span 
    978. 

  978. class="cmtt-10">&#x00A0;line</span>
    979. 

  979. <br class="fancyvrb" /><a 
    980. 

  980.  id="x1-23034r17"></a><span 
    981. 

  981. class="cmtt-10">&#x00A0;</span><span 
    982. 

  982. class="cmtt-10">&#x00A0;</span><span 
    983. 

  983. class="cmtt-10">&#x00A0;</span><span 
    984. 

  984. class="cmtt-10">&#x00A0;</span><span 
    985. 

  985. class="cmtt-10">&#x00A0;</span><span 
    986. 

  986. class="cmtt-10">&#x00A0;</span><span 
    987. 

  987. class="cmtt-10">&#x00A0;</span><span 
    988. 

  988. class="cmtt-10">&#x00A0;</span><span 
    989. 

  989. class="cmtt-10">&#x00A0;options.</span><span 
    990. 

  990. class="cmtt-10">&#x00A0;Memory</span><span 
    991. 

  991. class="cmtt-10">&#x00A0;bounds</span><span 
    992. 

  992. class="cmtt-10">&#x00A0;are</span><span 
    993. 

  993. class="cmtt-10">&#x00A0;in</span><span 
    994. 

  994. class="cmtt-10">&#x00A0;words,</span><span 
    995. 

  995. class="cmtt-10">&#x00A0;more</span><span 
    996. 

  996. class="cmtt-10">&#x00A0;or</span><span 
    997. 

  997. class="cmtt-10">&#x00A0;less,</span><span 
    998. 

  998. class="cmtt-10">&#x00A0;and</span><span 
    999. 

  999. class="cmtt-10">&#x00A0;CPU</span><span 
    1000. 

  1000. class="cmtt-10">&#x00A0;</span><span 
    1001. 

  1001. class="cmtt-10">&#x00A0;bounds</span><span 
    1002. 

  1002. class="cmtt-10">&#x00A0;</span><span 
    1003. 

  1003. class="cmtt-10">&#x00A0;are</span>
    1004. 

  1004. <br class="fancyvrb" /><a 
    1005. 

  1005.  id="x1-23036r18"></a><span 
    1006. 

  1006. class="cmtt-10">&#x00A0;</span><span 
    1007. 

  1007. class="cmtt-10">&#x00A0;</span><span 
    1008. 

  1008. class="cmtt-10">&#x00A0;</span><span 
    1009. 

  1009. class="cmtt-10">&#x00A0;</span><span 
    1010. 

  1010. class="cmtt-10">&#x00A0;</span><span 
    1011. 

  1011. class="cmtt-10">&#x00A0;</span><span 
    1012. 

  1012. class="cmtt-10">&#x00A0;</span><span 
    1013. 

  1013. class="cmtt-10">&#x00A0;</span><span 
    1014. 

  1014. class="cmtt-10">&#x00A0;in</span><span 
    1015. 

  1015. class="cmtt-10">&#x00A0;arbitrary</span><span 
    1016. 

  1016. class="cmtt-10">&#x00A0;units.</span>
    1017. 

  1017. <br class="fancyvrb" /><a 
    1018. 

  1018.  id="x1-23038r19"></a><span 
    1019. 

  1019. class="cmtt-10">&#x00A0;</span><span 
    1020. 

  1020. class="cmtt-10">&#x00A0;</span>
    1021. 

  1021. <br class="fancyvrb" /><a 
    1022. 

  1022.  id="x1-23040r20"></a><span 
    1023. 

  1023. class="cmtt-10">&#x00A0;</span><span 
    1024. 

  1024. class="cmtt-10">&#x00A0;DESCRIPTION</span>
    1025. 

  1025. <br class="fancyvrb" /><a 
    1026. 

  1026.  id="x1-23042r21"></a><span 
    1027. 

  1027. class="cmtt-10">&#x00A0;</span><span 
    1028. 

  1028. class="cmtt-10">&#x00A0;</span><span 
    1029. 

  1029. class="cmtt-10">&#x00A0;</span><span 
    1030. 

  1030. class="cmtt-10">&#x00A0;</span><span 
    1031. 

  1031. class="cmtt-10">&#x00A0;</span><span 
    1032. 

  1032. class="cmtt-10">&#x00A0;</span><span 
    1033. 

  1033. class="cmtt-10">&#x00A0;</span><span 
    1034. 

  1034. class="cmtt-10">&#x00A0;</span><span 
    1035. 

  1035. class="cmtt-10">&#x00A0;pfc</span><span 
    1036. 

  1036. class="cmtt-10">&#x00A0;is</span><span 
    1037. 

  1037. class="cmtt-10">&#x00A0;a</span><span 
    1038. 

  1038. class="cmtt-10">&#x00A0;compiler</span><span 
    1039. 

  1039. class="cmtt-10">&#x00A0;that</span><span 
    1040. 

  1040. class="cmtt-10">&#x00A0;compiles</span><span 
    1041. 

  1041. class="cmtt-10">&#x00A0;programs</span><span 
    1042. 

  1042. class="cmtt-10">&#x00A0;written</span><span 
    1043. 

  1043. class="cmtt-10">&#x00A0;in</span><span 
    1044. 

  1044. class="cmtt-10">&#x00A0;Piffle.</span><span 
    1045. 

  1045. class="cmtt-10">&#x00A0;It</span><span 
    1046. 

  1046. class="cmtt-10">&#x00A0;produces</span>
    1047. 

  1047. <br class="fancyvrb" /><a 
    1048. 

  1048.  id="x1-23044r22"></a><span 
    1049. 

  1049. class="cmtt-10">&#x00A0;</span><span 
    1050. 

  1050. class="cmtt-10">&#x00A0;</span><span 
    1051. 

  1051. class="cmtt-10">&#x00A0;</span><span 
    1052. 

  1052. class="cmtt-10">&#x00A0;</span><span 
    1053. 

  1053. class="cmtt-10">&#x00A0;</span><span 
    1054. 

  1054. class="cmtt-10">&#x00A0;</span><span 
    1055. 

  1055. class="cmtt-10">&#x00A0;</span><span 
    1056. 

  1056. class="cmtt-10">&#x00A0;</span><span 
    1057. 

  1057. class="cmtt-10">&#x00A0;a</span><span 
    1058. 

  1058. class="cmtt-10">&#x00A0;C</span><span 
    1059. 

  1059. class="cmtt-10">&#x00A0;file,</span><span 
    1060. 

  1060. class="cmtt-10">&#x00A0;which</span><span 
    1061. 

  1061. class="cmtt-10">&#x00A0;must</span><span 
    1062. 

  1062. class="cmtt-10">&#x00A0;be</span><span 
    1063. 

  1063. class="cmtt-10">&#x00A0;further</span><span 
    1064. 

  1064. class="cmtt-10">&#x00A0;processed</span><span 
    1065. 

  1065. class="cmtt-10">&#x00A0;</span><span 
    1066. 

  1066. class="cmtt-10">&#x00A0;with</span><span 
    1067. 

  1067. class="cmtt-10">&#x00A0;</span><span 
    1068. 

  1068. class="cmtt-10">&#x00A0;the</span><span 
    1069. 

  1069. class="cmtt-10">&#x00A0;</span><span 
    1070. 

  1070. class="cmtt-10">&#x00A0;GNU</span><span 
    1071. 

  1071. class="cmtt-10">&#x00A0;</span><span 
    1072. 

  1072. class="cmtt-10">&#x00A0;C</span><span 
    1073. 

  1073. class="cmtt-10">&#x00A0;</span><span 
    1074. 

  1074. class="cmtt-10">&#x00A0;compiler.</span>
    1075. 

  1075. <br class="fancyvrb" /><a 
    1076. 

  1076.  id="x1-23046r23"></a><span 
    1077. 

  1077. class="cmtt-10">&#x00A0;</span><span 
    1078. 

  1078. class="cmtt-10">&#x00A0;</span><span 
    1079. 

  1079. class="cmtt-10">&#x00A0;</span><span 
    1080. 

  1080. class="cmtt-10">&#x00A0;</span><span 
    1081. 

  1081. class="cmtt-10">&#x00A0;</span><span 
    1082. 

  1082. class="cmtt-10">&#x00A0;</span><span 
    1083. 

  1083. class="cmtt-10">&#x00A0;</span><span 
    1084. 

  1084. class="cmtt-10">&#x00A0;</span><span 
    1085. 

  1085. class="cmtt-10">&#x00A0;Typically,</span><span 
    1086. 

  1086. class="cmtt-10">&#x00A0;you</span><span 
    1087. 

  1087. class="cmtt-10">&#x00A0;would</span><span 
    1088. 

  1088. class="cmtt-10">&#x00A0;use</span><span 
    1089. 

  1089. class="cmtt-10">&#x00A0;pfc</span><span 
    1090. 

  1090. class="cmtt-10">&#x00A0;like</span><span 
    1091. 

  1091. class="cmtt-10">&#x00A0;this:</span>
    1092. 

  1092. <br class="fancyvrb" /><a 
    1093. 

  1093.  id="x1-23048r24"></a><span 
    1094. 

  1094. class="cmtt-10">&#x00A0;</span><span 
    1095. 

  1095. class="cmtt-10">&#x00A0;</span>
    1096. 

  1096. <br class="fancyvrb" /><a 
    1097. 

  1097.  id="x1-23050r25"></a><span 
    1098. 

  1098. class="cmtt-10">&#x00A0;</span><span 
    1099. 

  1099. class="cmtt-10">&#x00A0;</span><span 
    1100. 

  1100. class="cmtt-10">&#x00A0;</span><span 
    1101. 

  1101. class="cmtt-10">&#x00A0;</span><span 
    1102. 

  1102. class="cmtt-10">&#x00A0;</span><span 
    1103. 

  1103. class="cmtt-10">&#x00A0;</span><span 
    1104. 

  1104. class="cmtt-10">&#x00A0;</span><span 
    1105. 

  1105. class="cmtt-10">&#x00A0;</span><span 
    1106. 

  1106. class="cmtt-10">&#x00A0;</span><span 
    1107. 

  1107. class="cmtt-10">&#x00A0;</span><span 
    1108. 

  1108. class="cmtt-10">&#x00A0;</span><span 
    1109. 

  1109. class="cmtt-10">&#x00A0;</span><span 
    1110. 

  1110. class="cmtt-10">&#x00A0;</span><span 
    1111. 

  1111. class="cmtt-10">&#x00A0;</span><span 
    1112. 

  1112. class="cmtt-10">&#x00A0;</span><span 
    1113. 

  1113. class="cmtt-10">&#x00A0;pfc</span><span 
    1114. 

  1114. class="cmtt-10">&#x00A0;-Bpcap.c</span><span 
    1115. 

  1115. class="cmtt-10">&#x00A0;foo.pfl</span>
    1116. 

  1116. <br class="fancyvrb" /><a 
    1117. 

  1117.  id="x1-23052r26"></a><span 
    1118. 

  1118. class="cmtt-10">&#x00A0;</span><span 
    1119. 

  1119. class="cmtt-10">&#x00A0;</span>
    1120. 

  1120. <br class="fancyvrb" /><a 
    1121. 

  1121.  id="x1-23054r27"></a><span 
    1122. 

  1122. class="cmtt-10">&#x00A0;</span><span 
    1123. 

  1123. class="cmtt-10">&#x00A0;</span><span 
    1124. 

  1124. class="cmtt-10">&#x00A0;</span><span 
    1125. 

  1125. class="cmtt-10">&#x00A0;</span><span 
    1126. 

  1126. class="cmtt-10">&#x00A0;</span><span 
    1127. 

  1127. class="cmtt-10">&#x00A0;</span><span 
    1128. 

  1128. class="cmtt-10">&#x00A0;</span><span 
    1129. 

  1129. class="cmtt-10">&#x00A0;</span><span 
    1130. 

  1130. class="cmtt-10">&#x00A0;That</span><span 
    1131. 

  1131. class="cmtt-10">&#x00A0;</span><span 
    1132. 

  1132. class="cmtt-10">&#x00A0;would</span><span 
    1133. 

  1133. class="cmtt-10">&#x00A0;</span><span 
    1134. 

  1134. class="cmtt-10">&#x00A0;compile</span><span 
    1135. 

  1135. class="cmtt-10">&#x00A0;foo.pfl</span><span 
    1136. 

  1136. class="cmtt-10">&#x00A0;into</span><span 
    1137. 

  1137. class="cmtt-10">&#x00A0;a</span><span 
    1138. 

  1138. class="cmtt-10">&#x00A0;new</span><span 
    1139. 

  1139. class="cmtt-10">&#x00A0;file</span><span 
    1140. 

  1140. class="cmtt-10">&#x00A0;called</span><span 
    1141. 

  1141. class="cmtt-10">&#x00A0;foo.c,</span><span 
    1142. 

  1142. class="cmtt-10">&#x00A0;and</span><span 
    1143. 

  1143. class="cmtt-10">&#x00A0;it</span><span 
    1144. 

  1144. class="cmtt-10">&#x00A0;would</span>
    1145. 

  1145. <br class="fancyvrb" /><a 
    1146. 

  1146.  id="x1-23056r28"></a><span 
    1147. 

  1147. class="cmtt-10">&#x00A0;</span><span 
    1148. 

  1148. class="cmtt-10">&#x00A0;</span><span 
    1149. 

  1149. class="cmtt-10">&#x00A0;</span><span 
    1150. 

  1150. class="cmtt-10">&#x00A0;</span><span 
    1151. 

  1151. class="cmtt-10">&#x00A0;</span><span 
    1152. 

  1152. class="cmtt-10">&#x00A0;</span><span 
    1153. 

  1153. class="cmtt-10">&#x00A0;</span><span 
    1154. 

  1154. class="cmtt-10">&#x00A0;</span><span 
    1155. 

  1155. class="cmtt-10">&#x00A0;embed</span><span 
    1156. 

  1156. class="cmtt-10">&#x00A0;the</span><span 
    1157. 

  1157. class="cmtt-10">&#x00A0;pcap.c</span><span 
    1158. 

  1158. class="cmtt-10">&#x00A0;boilerplate,</span><span 
    1159. 

  1159. class="cmtt-10">&#x00A0;which</span><span 
    1160. 

  1160. class="cmtt-10">&#x00A0;is</span><span 
    1161. 

  1161. class="cmtt-10">&#x00A0;the</span><span 
    1162. 

  1162. class="cmtt-10">&#x00A0;one</span><span 
    1163. 

  1163. class="cmtt-10">&#x00A0;you</span><span 
    1164. 

  1164. class="cmtt-10">&#x00A0;should</span><span 
    1165. 

  1165. class="cmtt-10">&#x00A0;use</span><span 
    1166. 

  1166. class="cmtt-10">&#x00A0;when</span><span 
    1167. 

  1167. class="cmtt-10">&#x00A0;</span><span 
    1168. 

  1168. class="cmtt-10">&#x00A0;you</span>
    1169. 

  1169. <br class="fancyvrb" /><a 
    1170. 

  1170.  id="x1-23058r29"></a><span 
    1171. 

  1171. class="cmtt-10">&#x00A0;</span><span 
    1172. 

  1172. class="cmtt-10">&#x00A0;</span><span 
    1173. 

  1173. class="cmtt-10">&#x00A0;</span><span 
    1174. 

  1174. class="cmtt-10">&#x00A0;</span><span 
    1175. 

  1175. class="cmtt-10">&#x00A0;</span><span 
    1176. 

  1176. class="cmtt-10">&#x00A0;</span><span 
    1177. 

  1177. class="cmtt-10">&#x00A0;</span><span 
    1178. 

  1178. class="cmtt-10">&#x00A0;</span><span 
    1179. 

  1179. class="cmtt-10">&#x00A0;want</span><span 
    1180. 

  1180. class="cmtt-10">&#x00A0;</span><span 
    1181. 

  1181. class="cmtt-10">&#x00A0;to</span><span 
    1182. 

  1182. class="cmtt-10">&#x00A0;</span><span 
    1183. 

  1183. class="cmtt-10">&#x00A0;use</span><span 
    1184. 

  1184. class="cmtt-10">&#x00A0;the</span><span 
    1185. 

  1185. class="cmtt-10">&#x00A0;pcap</span><span 
    1186. 

  1186. class="cmtt-10">&#x00A0;library.</span><span 
    1187. 

  1187. class="cmtt-10">&#x00A0;Next,</span><span 
    1188. 

  1188. class="cmtt-10">&#x00A0;you</span><span 
    1189. 

  1189. class="cmtt-10">&#x00A0;would</span><span 
    1190. 

  1190. class="cmtt-10">&#x00A0;compile</span><span 
    1191. 

  1191. class="cmtt-10">&#x00A0;the</span><span 
    1192. 

  1192. class="cmtt-10">&#x00A0;resulting</span><span 
    1193. 

  1193. class="cmtt-10">&#x00A0;C</span>
    1194. 

  1194. <br class="fancyvrb" /><a 
    1195. 

  1195.  id="x1-23060r30"></a><span 
    1196. 

  1196. class="cmtt-10">&#x00A0;</span><span 
    1197. 

  1197. class="cmtt-10">&#x00A0;</span><span 
    1198. 

  1198. class="cmtt-10">&#x00A0;</span><span 
    1199. 

  1199. class="cmtt-10">&#x00A0;</span><span 
    1200. 

  1200. class="cmtt-10">&#x00A0;</span><span 
    1201. 

  1201. class="cmtt-10">&#x00A0;</span><span 
    1202. 

  1202. class="cmtt-10">&#x00A0;</span><span 
    1203. 

  1203. class="cmtt-10">&#x00A0;</span><span 
    1204. 

  1204. class="cmtt-10">&#x00A0;program</span><span 
    1205. 

  1205. class="cmtt-10">&#x00A0;with</span>
    1206. 

  1206. <br class="fancyvrb" /><a 
    1207. 

  1207.  id="x1-23062r31"></a><span 
    1208. 

  1208. class="cmtt-10">&#x00A0;</span><span 
    1209. 

  1209. class="cmtt-10">&#x00A0;</span>
    1210. 

  1210. <br class="fancyvrb" /><a 
    1211. 

  1211.  id="x1-23064r32"></a><span 
    1212. 

  1212. class="cmtt-10">&#x00A0;</span><span 
    1213. 

  1213. class="cmtt-10">&#x00A0;</span><span 
    1214. 

  1214. class="cmtt-10">&#x00A0;</span><span 
    1215. 

  1215. class="cmtt-10">&#x00A0;</span><span 
    1216. 

  1216. class="cmtt-10">&#x00A0;</span><span 
    1217. 

  1217. class="cmtt-10">&#x00A0;</span><span 
    1218. 

  1218. class="cmtt-10">&#x00A0;</span><span 
    1219. 

  1219. class="cmtt-10">&#x00A0;</span><span 
    1220. 

  1220. class="cmtt-10">&#x00A0;</span><span 
    1221. 

  1221. class="cmtt-10">&#x00A0;</span><span 
    1222. 

  1222. class="cmtt-10">&#x00A0;</span><span 
    1223. 

  1223. class="cmtt-10">&#x00A0;</span><span 
    1224. 

  1224. class="cmtt-10">&#x00A0;</span><span 
    1225. 

  1225. class="cmtt-10">&#x00A0;</span><span 
    1226. 

  1226. class="cmtt-10">&#x00A0;</span><span 
    1227. 

  1227. class="cmtt-10">&#x00A0;cc</span><span 
    1228. 

  1228. class="cmtt-10">&#x00A0;-o</span><span 
    1229. 

  1229. class="cmtt-10">&#x00A0;foo</span><span 
    1230. 

  1230. class="cmtt-10">&#x00A0;foo.pfl</span><span 
    1231. 

  1231. class="cmtt-10">&#x00A0;-lpcap</span>
    1232. 

  1232. <br class="fancyvrb" /><a 
    1233. 

  1233.  id="x1-23066r33"></a><span 
    1234. 

  1234. class="cmtt-10">&#x00A0;</span><span 
    1235. 

  1235. class="cmtt-10">&#x00A0;</span>
    1236. 

  1236. <br class="fancyvrb" /><a 
    1237. 

  1237.  id="x1-23068r34"></a><span 
    1238. 

  1238. class="cmtt-10">&#x00A0;</span><span 
    1239. 

  1239. class="cmtt-10">&#x00A0;OPTIONS</span>
    1240. 

  1240. <br class="fancyvrb" /><a 
    1241. 

  1241.  id="x1-23070r35"></a><span 
    1242. 

  1242. class="cmtt-10">&#x00A0;</span><span 
    1243. 

  1243. class="cmtt-10">&#x00A0;</span><span 
    1244. 

  1244. class="cmtt-10">&#x00A0;</span><span 
    1245. 

  1245. class="cmtt-10">&#x00A0;</span><span 
    1246. 

  1246. class="cmtt-10">&#x00A0;</span><span 
    1247. 

  1247. class="cmtt-10">&#x00A0;</span><span 
    1248. 

  1248. class="cmtt-10">&#x00A0;</span><span 
    1249. 

  1249. class="cmtt-10">&#x00A0;</span><span 
    1250. 

  1250. class="cmtt-10">&#x00A0;-h</span><span 
    1251. 

  1251. class="cmtt-10">&#x00A0;or</span><span 
    1252. 

  1252. class="cmtt-10">&#x00A0;--help</span>
    1253. 

  1253. <br class="fancyvrb" /><a 
    1254. 

  1254.  id="x1-23072r36"></a><span 
    1255. 

  1255. class="cmtt-10">&#x00A0;</span><span 
    1256. 

  1256. class="cmtt-10">&#x00A0;</span>
    1257. 

  1257. <br class="fancyvrb" /><a 
    1258. 

  1258.  id="x1-23074r37"></a><span 
    1259. 

  1259. class="cmtt-10">&#x00A0;</span><span 
    1260. 

  1260. class="cmtt-10">&#x00A0;</span><span 
    1261. 

  1261. class="cmtt-10">&#x00A0;</span><span 
    1262. 

  1262. class="cmtt-10">&#x00A0;</span><span 
    1263. 

  1263. class="cmtt-10">&#x00A0;</span><span 
    1264. 

  1264. class="cmtt-10">&#x00A0;</span><span 
    1265. 

  1265. class="cmtt-10">&#x00A0;</span><span 
    1266. 

  1266. class="cmtt-10">&#x00A0;</span><span 
    1267. 

  1267. class="cmtt-10">&#x00A0;</span><span 
    1268. 

  1268. class="cmtt-10">&#x00A0;</span><span 
    1269. 

  1269. class="cmtt-10">&#x00A0;</span><span 
    1270. 

  1270. class="cmtt-10">&#x00A0;</span><span 
    1271. 

  1271. class="cmtt-10">&#x00A0;</span><span 
    1272. 

  1272. class="cmtt-10">&#x00A0;</span><span 
    1273. 

  1273. class="cmtt-10">&#x00A0;</span><span 
    1274. 

  1274. class="cmtt-10">&#x00A0;Prints</span><span 
    1275. 

  1275. class="cmtt-10">&#x00A0;a</span><span 
    1276. 

  1276. class="cmtt-10">&#x00A0;short</span><span 
    1277. 

  1277. class="cmtt-10">&#x00A0;usage</span><span 
    1278. 

  1278. class="cmtt-10">&#x00A0;message.</span>
    1279. 

  1279. <br class="fancyvrb" /><a 
    1280. 

  1280.  id="x1-23076r38"></a><span 
    1281. 

  1281. class="cmtt-10">&#x00A0;</span><span 
    1282. 

  1282. class="cmtt-10">&#x00A0;</span>
    1283. 

  1283. 

  1284. <br class="fancyvrb" /><a 
    1285. 

  1285.  id="x1-23078r39"></a><span 
    1286. 

  1286. class="cmtt-10">&#x00A0;</span><span 
    1287. 

  1287. class="cmtt-10">&#x00A0;</span><span 
    1288. 

  1288. class="cmtt-10">&#x00A0;</span><span 
    1289. 

  1289. class="cmtt-10">&#x00A0;</span><span 
    1290. 

  1290. class="cmtt-10">&#x00A0;</span><span 
    1291. 

  1291. class="cmtt-10">&#x00A0;</span><span 
    1292. 

  1292. class="cmtt-10">&#x00A0;</span><span 
    1293. 

  1293. class="cmtt-10">&#x00A0;</span><span 
    1294. 

  1294. class="cmtt-10">&#x00A0;-a</span><span 
    1295. 

  1295. class="cmtt-10">&#x00A0;or</span><span 
    1296. 

  1296. class="cmtt-10">&#x00A0;--ansicolors</span>
    1297. 

  1297. <br class="fancyvrb" /><a 
    1298. 

  1298.  id="x1-23080r40"></a><span 
    1299. 

  1299. class="cmtt-10">&#x00A0;</span><span 
    1300. 

  1300. class="cmtt-10">&#x00A0;</span>
    1301. 

  1301. <br class="fancyvrb" /><a 
    1302. 

  1302.  id="x1-23082r41"></a><span 
    1303. 

  1303. class="cmtt-10">&#x00A0;</span><span 
    1304. 

  1304. class="cmtt-10">&#x00A0;</span><span 
    1305. 

  1305. class="cmtt-10">&#x00A0;</span><span 
    1306. 

  1306. class="cmtt-10
    1307.