various security fixes and precautionary checks
[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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 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
49 /* lets disallow possible ambiguous cases */
50 if(size > INT_MAX)
51 return NULL;
52
53 #ifdef MEMALIGN_HACK
54 int diff;
55 ptr = malloc(size+16+1);
56 diff= ((-(int)ptr - 1)&15) + 1;
57 ptr += diff;
58 ((char*)ptr)[-1]= diff;
59 #elif defined (HAVE_MEMALIGN)
60 ptr = memalign(16,size);
61 /* Why 64?
62 Indeed, we should align it:
63 on 4 for 386
64 on 16 for 486
65 on 32 for 586, PPro - k6-III
66 on 64 for K7 (maybe for P3 too).
67 Because L1 and L2 caches are aligned on those values.
68 But I don't want to code such logic here!
69 */
70 /* Why 16?
71 because some cpus need alignment, for example SSE2 on P4, & most RISC cpus
72 it will just trigger an exception and the unaligned load will be done in the
73 exception handler or it will just segfault (SSE2 on P4)
74 Why not larger? because i didnt see a difference in benchmarks ...
75 */
76 /* benchmarks with p3
77 memalign(64)+1 3071,3051,3032
78 memalign(64)+2 3051,3032,3041
79 memalign(64)+4 2911,2896,2915
80 memalign(64)+8 2545,2554,2550
81 memalign(64)+16 2543,2572,2563
82 memalign(64)+32 2546,2545,2571
83 memalign(64)+64 2570,2533,2558
84
85 btw, malloc seems to do 8 byte alignment by default here
86 */
87 #else
88 ptr = malloc(size);
89 #endif
90 return ptr;
91 }
92
93 /**
94 * av_realloc semantics (same as glibc): if ptr is NULL and size > 0,
95 * identical to malloc(size). If size is zero, it is identical to
96 * free(ptr) and NULL is returned.
97 */
98 void *av_realloc(void *ptr, unsigned int size)
99 {
100 /* lets disallow possible ambiguous cases */
101 if(size > INT_MAX)
102 return NULL;
103
104 #ifdef MEMALIGN_HACK
105 //FIXME this isnt aligned correctly though it probably isnt needed
106 int diff;
107 if(!ptr) return av_malloc(size);
108 diff= ((char*)ptr)[-1];
109 return realloc(ptr - diff, size + diff) + diff;
110 #else
111 return realloc(ptr, size);
112 #endif
113 }
114
115 /* NOTE: ptr = NULL is explicetly allowed */
116 void av_free(void *ptr)
117 {
118 /* XXX: this test should not be needed on most libcs */
119 if (ptr)
120 #ifdef MEMALIGN_HACK
121 free(ptr - ((char*)ptr)[-1]);
122 #else
123 free(ptr);
124 #endif
125 }
126