/vendor/gc/include/gc_tiny_fl.h

 1/* 
 2 * Copyright (c) 1999-2005 Hewlett-Packard Development Company, L.P.
 3 *
 4 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 5 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 6 *
 7 * Permission is hereby granted to use or copy this program
 8 * for any purpose,  provided the above notices are retained on all copies.
 9 * Permission to modify the code and to distribute modified code is granted,
10 * provided the above notices are retained, and a notice that the code was
11 * modified is included with the above copyright notice.
12 */
13
14#ifndef GC_TINY_FL_H
15#define GC_TINY_FL_H
16/*
17 * Constants and data structures for "tiny" free lists.
18 * These are used for thread-local allocation or in-lined allocators.
19 * Each global free list also essentially starts with one of these.
20 * However, global free lists are known to the GC.  "Tiny" free lists
21 * are basically private to the client.  Their contents are viewed as
22 * "in use" and marked accordingly by the core of the GC.
23 * 
24 * Note that inlined code might know about the layout of these and the constants
25 * involved.  Thus any change here may invalidate clients, and such changes should
26 * be avoided.  Hence we keep this as simple as possible.
27 */
28
29/*
30 * We always set GC_GRANULE_BYTES to twice the length of a pointer.
31 * This means that all allocation requests are rounded up to the next
32 * multiple of 16 on 64-bit architectures or 8 on 32-bit architectures.
33 * This appears to be a reasonable compromise between fragmentation overhead
34 * and space usage for mark bits (usually mark bytes).
35 * On many 64-bit architectures some memory references require 16-byte
36 * alignment, making this necessary anyway.
37 * For a few 32-bit architecture (e.g. x86), we may also need 16-byte alignment
38 * for certain memory references.  But currently that does not seem to be the
39 * default for all conventional malloc implementations, so we ignore that
40 * problem.
41 * It would always be safe, and often useful, to be able to allocate very
42 * small objects with smaller alignment.  But that would cost us mark bit
43 * space, so we no longer do so.
44 */
45#ifndef GC_GRANULE_BYTES
46  /* GC_GRANULE_BYTES should not be overridden in any instances of the GC */
47  /* library that may be shared between applications, since it affects	  */
48  /* the binary interface to the library.				  */
49# if defined(__LP64__) || defined (_LP64) || defined(_WIN64) \
50	|| defined(__s390x__) || defined(__x86_64__) \
51	|| defined(__alpha__) || defined(__powerpc64__) \
52	|| defined(__arch64__)
53#  define GC_GRANULE_BYTES 16
54#  define GC_GRANULE_WORDS 2
55# else
56#  define GC_GRANULE_BYTES 8
57#  define GC_GRANULE_WORDS 2
58# endif
59#endif /* !GC_GRANULE_BYTES */
60
61#if GC_GRANULE_WORDS == 2
62#  define GC_WORDS_TO_GRANULES(n) ((n)>>1)
63#else
64#  define GC_WORDS_TO_GRANULES(n) ((n)*sizeof(void *)/GC_GRANULE_BYTES)
65#endif
66
67/* A "tiny" free list header contains TINY_FREELISTS pointers to 	*/
68/* singly linked lists of objects of different sizes, the ith one	*/
69/* containing objects i granules in size.  Note that there is a list	*/
70/* of size zero objects.						*/
71#ifndef GC_TINY_FREELISTS
72# if GC_GRANULE_BYTES == 16
73#   define GC_TINY_FREELISTS 25
74# else
75#   define GC_TINY_FREELISTS 33	/* Up to and including 256 bytes */
76# endif
77#endif /* !GC_TINY_FREELISTS */
78
79/* The ith free list corresponds to size i*GC_GRANULE_BYTES	*/
80/* Internally to the collector, the index can be computed with	*/
81/* ROUNDED_UP_GRANULES.  Externally, we don't know whether	*/
82/* DONT_ADD_BYTE_AT_END is set, but the client should know.	*/
83
84/* Convert a free list index to the actual size of objects	*/
85/* on that list, including extra space we added.  Not an	*/
86/* inverse of the above.					*/
87#define GC_RAW_BYTES_FROM_INDEX(i) ((i) * GC_GRANULE_BYTES)
88
89#endif /* GC_TINY_FL_H */