spelling fixes courtesy of "Hervé W." H.O.W.aka.V+ffmpeg (at) gmail (dot) com
[libav.git] / libavcodec / mem.c
1 /*
2 * default memory allocator for libavcodec
3 * Copyright (c) 2002 Fabrice Bellard.
4 *
5 * This library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Lesser General Public
7 * License as published by the Free Software Foundation; either
8 * version 2 of the License, or (at your option) any later version.
9 *
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Lesser General Public License for more details.
14 *
15 * You should have received a copy of the GNU Lesser General Public
16 * License along with this library; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
18 */
19
20 /**
21 * @file mem.c
22 * default memory allocator for libavcodec.
23 */
24
25 #include "avcodec.h"
26
27 /* here we can use OS dependant allocation functions */
28 #undef malloc
29 #undef free
30 #undef realloc
31
32 #ifdef HAVE_MALLOC_H
33 #include <malloc.h>
34 #endif
35
36 /* you can redefine av_malloc and av_free in your project to use your
37 memory allocator. You do not need to suppress this file because the
38 linker will do it automatically */
39
40 /**
41 * Memory allocation of size byte with alignment suitable for all
42 * memory accesses (including vectors if available on the
43 * CPU). av_malloc(0) must return a non NULL pointer.
44 */
45 void *av_malloc(unsigned int size)
46 {
47 void *ptr;
48 #ifdef MEMALIGN_HACK
49 long diff;
50 #endif
51
52 /* let's disallow possible ambiguous cases */
53 if(size > INT_MAX)
54 return NULL;
55
56 #ifdef MEMALIGN_HACK
57 ptr = malloc(size+16+1);
58 diff= ((-(long)ptr - 1)&15) + 1;
59 ptr += diff;
60 ((char*)ptr)[-1]= diff;
61 #elif defined (HAVE_MEMALIGN)
62 ptr = memalign(16,size);
63 /* Why 64?
64 Indeed, we should align it:
65 on 4 for 386
66 on 16 for 486
67 on 32 for 586, PPro - k6-III
68 on 64 for K7 (maybe for P3 too).
69 Because L1 and L2 caches are aligned on those values.
70 But I don't want to code such logic here!
71 */
72 /* Why 16?
73 because some cpus need alignment, for example SSE2 on P4, & most RISC cpus
74 it will just trigger an exception and the unaligned load will be done in the
75 exception handler or it will just segfault (SSE2 on P4)
76 Why not larger? because i didnt see a difference in benchmarks ...
77 */
78 /* benchmarks with p3
79 memalign(64)+1 3071,3051,3032
80 memalign(64)+2 3051,3032,3041
81 memalign(64)+4 2911,2896,2915
82 memalign(64)+8 2545,2554,2550
83 memalign(64)+16 2543,2572,2563
84 memalign(64)+32 2546,2545,2571
85 memalign(64)+64 2570,2533,2558
86
87 btw, malloc seems to do 8 byte alignment by default here
88 */
89 #else
90 ptr = malloc(size);
91 #endif
92 return ptr;
93 }
94
95 /**
96 * av_realloc semantics (same as glibc): if ptr is NULL and size > 0,
97 * identical to malloc(size). If size is zero, it is identical to
98 * free(ptr) and NULL is returned.
99 */
100 void *av_realloc(void *ptr, unsigned int size)
101 {
102 #ifdef MEMALIGN_HACK
103 int diff;
104 #endif
105
106 /* let's disallow possible ambiguous cases */
107 if(size > INT_MAX)
108 return NULL;
109
110 #ifdef MEMALIGN_HACK
111 //FIXME this isn't aligned correctly, though it probably isn't needed
112 if(!ptr) return av_malloc(size);
113 diff= ((char*)ptr)[-1];
114 return realloc(ptr - diff, size + diff) + diff;
115 #else
116 return realloc(ptr, size);
117 #endif
118 }
119
120 /**
121 * Free memory which has been allocated with av_malloc(z)() or av_realloc().
122 * NOTE: ptr = NULL is explicetly allowed
123 * Note2: it is recommanded that you use av_freep() instead
124 */
125 void av_free(void *ptr)
126 {
127 /* XXX: this test should not be needed on most libcs */
128 if (ptr)
129 #ifdef MEMALIGN_HACK
130 free(ptr - ((char*)ptr)[-1]);
131 #else
132 free(ptr);
133 #endif
134 }
135