/lua/lbitlib.c

  1/*
  2** $Id: lbitlib.c,v 1.18.1.2 2013/07/09 18:01:41 roberto Exp $
  3** Standard library for bitwise operations
  4** See Copyright Notice in lua.h
  5*/
  6
  7#define lbitlib_c
  8#define LUA_LIB
  9
 10#include "lua.h"
 11
 12#include "lauxlib.h"
 13#include "lualib.h"
 14
 15
 16/* number of bits to consider in a number */
 17#if !defined(LUA_NBITS)
 18#define LUA_NBITS	32
 19#endif
 20
 21
 22#define ALLONES		(~(((~(lua_Unsigned)0) << (LUA_NBITS - 1)) << 1))
 23
 24/* macro to trim extra bits */
 25#define trim(x)		((x) & ALLONES)
 26
 27
 28/* builds a number with 'n' ones (1 <= n <= LUA_NBITS) */
 29#define mask(n)		(~((ALLONES << 1) << ((n) - 1)))
 30
 31
 32typedef lua_Unsigned b_uint;
 33
 34
 35
 36static b_uint andaux (lua_State *L) {
 37  int i, n = lua_gettop(L);
 38  b_uint r = ~(b_uint)0;
 39  for (i = 1; i <= n; i++)
 40    r &= luaL_checkunsigned(L, i);
 41  return trim(r);
 42}
 43
 44
 45static int b_and (lua_State *L) {
 46  b_uint r = andaux(L);
 47  lua_pushunsigned(L, r);
 48  return 1;
 49}
 50
 51
 52static int b_test (lua_State *L) {
 53  b_uint r = andaux(L);
 54  lua_pushboolean(L, r != 0);
 55  return 1;
 56}
 57
 58
 59static int b_or (lua_State *L) {
 60  int i, n = lua_gettop(L);
 61  b_uint r = 0;
 62  for (i = 1; i <= n; i++)
 63    r |= luaL_checkunsigned(L, i);
 64  lua_pushunsigned(L, trim(r));
 65  return 1;
 66}
 67
 68
 69static int b_xor (lua_State *L) {
 70  int i, n = lua_gettop(L);
 71  b_uint r = 0;
 72  for (i = 1; i <= n; i++)
 73    r ^= luaL_checkunsigned(L, i);
 74  lua_pushunsigned(L, trim(r));
 75  return 1;
 76}
 77
 78
 79static int b_not (lua_State *L) {
 80  b_uint r = ~luaL_checkunsigned(L, 1);
 81  lua_pushunsigned(L, trim(r));
 82  return 1;
 83}
 84
 85
 86static int b_shift (lua_State *L, b_uint r, int i) {
 87  if (i < 0) {  /* shift right? */
 88    i = -i;
 89    r = trim(r);
 90    if (i >= LUA_NBITS) r = 0;
 91    else r >>= i;
 92  }
 93  else {  /* shift left */
 94    if (i >= LUA_NBITS) r = 0;
 95    else r <<= i;
 96    r = trim(r);
 97  }
 98  lua_pushunsigned(L, r);
 99  return 1;
100}
101
102
103static int b_lshift (lua_State *L) {
104  return b_shift(L, luaL_checkunsigned(L, 1), luaL_checkint(L, 2));
105}
106
107
108static int b_rshift (lua_State *L) {
109  return b_shift(L, luaL_checkunsigned(L, 1), -luaL_checkint(L, 2));
110}
111
112
113static int b_arshift (lua_State *L) {
114  b_uint r = luaL_checkunsigned(L, 1);
115  int i = luaL_checkint(L, 2);
116  if (i < 0 || !(r & ((b_uint)1 << (LUA_NBITS - 1))))
117    return b_shift(L, r, -i);
118  else {  /* arithmetic shift for 'negative' number */
119    if (i >= LUA_NBITS) r = ALLONES;
120    else
121      r = trim((r >> i) | ~(~(b_uint)0 >> i));  /* add signal bit */
122    lua_pushunsigned(L, r);
123    return 1;
124  }
125}
126
127
128static int b_rot (lua_State *L, int i) {
129  b_uint r = luaL_checkunsigned(L, 1);
130  i &= (LUA_NBITS - 1);  /* i = i % NBITS */
131  r = trim(r);
132  if (i != 0)  /* avoid undefined shift of LUA_NBITS when i == 0 */
133    r = (r << i) | (r >> (LUA_NBITS - i));
134  lua_pushunsigned(L, trim(r));
135  return 1;
136}
137
138
139static int b_lrot (lua_State *L) {
140  return b_rot(L, luaL_checkint(L, 2));
141}
142
143
144static int b_rrot (lua_State *L) {
145  return b_rot(L, -luaL_checkint(L, 2));
146}
147
148
149/*
150** get field and width arguments for field-manipulation functions,
151** checking whether they are valid.
152** ('luaL_error' called without 'return' to avoid later warnings about
153** 'width' being used uninitialized.)
154*/
155static int fieldargs (lua_State *L, int farg, int *width) {
156  int f = luaL_checkint(L, farg);
157  int w = luaL_optint(L, farg + 1, 1);
158  luaL_argcheck(L, 0 <= f, farg, "field cannot be negative");
159  luaL_argcheck(L, 0 < w, farg + 1, "width must be positive");
160  if (f + w > LUA_NBITS)
161    luaL_error(L, "trying to access non-existent bits");
162  *width = w;
163  return f;
164}
165
166
167static int b_extract (lua_State *L) {
168  int w;
169  b_uint r = luaL_checkunsigned(L, 1);
170  int f = fieldargs(L, 2, &w);
171  r = (r >> f) & mask(w);
172  lua_pushunsigned(L, r);
173  return 1;
174}
175
176
177static int b_replace (lua_State *L) {
178  int w;
179  b_uint r = luaL_checkunsigned(L, 1);
180  b_uint v = luaL_checkunsigned(L, 2);
181  int f = fieldargs(L, 3, &w);
182  int m = mask(w);
183  v &= m;  /* erase bits outside given width */
184  r = (r & ~(m << f)) | (v << f);
185  lua_pushunsigned(L, r);
186  return 1;
187}
188
189
190static const luaL_Reg bitlib[] = {
191  {"arshift", b_arshift},
192  {"band", b_and},
193  {"bnot", b_not},
194  {"bor", b_or},
195  {"bxor", b_xor},
196  {"btest", b_test},
197  {"extract", b_extract},
198  {"lrotate", b_lrot},
199  {"lshift", b_lshift},
200  {"replace", b_replace},
201  {"rrotate", b_rrot},
202  {"rshift", b_rshift},
203  {NULL, NULL}
204};
205
206
207
208LUAMOD_API int luaopen_bit32 (lua_State *L) {
209  luaL_newlib(L, bitlib);
210  return 1;
211}
212