libavutil/mem.c

   1 /*
   2  * default memory allocator for libavutil
   3  * Copyright (c) 2002 Fabrice Bellard
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file libavutil/mem.c
  24  * default memory allocator for libavutil
  25  */
  26
  27 #include "config.h"
  28
  29 #include <limits.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #if HAVE_MALLOC_H
  33 #include <malloc.h>
  34 #endif
  35
  36 #include "mem.h"
  37
  38 /* here we can use OS-dependent allocation functions */
  39 #undef free
  40 #undef malloc
  41 #undef realloc
  42
  43 /* You can redefine av_malloc and av_free in your project to use your
  44    memory allocator. You do not need to suppress this file because the
  45    linker will do it automatically. */
  46
  47 void *av_malloc(unsigned int size)
  48 {
  49     void *ptr = NULL;
  50 #if CONFIG_MEMALIGN_HACK
  51     long diff;
  52 #endif
  53
  54     /* let's disallow possible ambiguous cases */
  55     if(size > (INT_MAX-16) )
  56         return NULL;
  57
  58 #if CONFIG_MEMALIGN_HACK
  59     ptr = malloc(size+16);
  60     if(!ptr)
  61         return ptr;
  62     diff= ((-(long)ptr - 1)&15) + 1;
  63     ptr = (char*)ptr + diff;
  64     ((char*)ptr)[-1]= diff;
  65 #elif HAVE_POSIX_MEMALIGN
  66     posix_memalign(&ptr,16,size);
  67 #elif HAVE_MEMALIGN
  68     ptr = memalign(16,size);
  69     /* Why 64?
  70        Indeed, we should align it:
  71          on 4 for 386
  72          on 16 for 486
  73          on 32 for 586, PPro - K6-III
  74          on 64 for K7 (maybe for P3 too).
  75        Because L1 and L2 caches are aligned on those values.
  76        But I don't want to code such logic here!
  77      */
  78      /* Why 16?
  79         Because some CPUs need alignment, for example SSE2 on P4, & most RISC CPUs
  80         it will just trigger an exception and the unaligned load will be done in the
  81         exception handler or it will just segfault (SSE2 on P4).
  82         Why not larger? Because I did not see a difference in benchmarks ...
  83      */
  84      /* benchmarks with P3
  85         memalign(64)+1          3071,3051,3032
  86         memalign(64)+2          3051,3032,3041
  87         memalign(64)+4          2911,2896,2915
  88         memalign(64)+8          2545,2554,2550
  89         memalign(64)+16         2543,2572,2563
  90         memalign(64)+32         2546,2545,2571
  91         memalign(64)+64         2570,2533,2558
  92
  93         BTW, malloc seems to do 8-byte alignment by default here.
  94      */
  95 #else
  96     ptr = malloc(size);
  97 #endif
  98     return ptr;
  99 }
 100
 101 void *av_realloc(void *ptr, unsigned int size)
 102 {
 103 #if CONFIG_MEMALIGN_HACK
 104     int diff;
 105 #endif
 106
 107     /* let's disallow possible ambiguous cases */
 108     if(size > (INT_MAX-16) )
 109         return NULL;
 110
 111 #if CONFIG_MEMALIGN_HACK
 112     //FIXME this isn't aligned correctly, though it probably isn't needed
 113     if(!ptr) return av_malloc(size);
 114     diff= ((char*)ptr)[-1];
 115     return (char*)realloc((char*)ptr - diff, size + diff) + diff;
 116 #else
 117     return realloc(ptr, size);
 118 #endif
 119 }
 120
 121 void av_free(void *ptr)
 122 {
 123     /* XXX: this test should not be needed on most libcs */
 124     if (ptr)
 125 #if CONFIG_MEMALIGN_HACK
 126         free((char*)ptr - ((char*)ptr)[-1]);
 127 #else
 128         free(ptr);
 129 #endif
 130 }
 131
 132 void av_freep(void *arg)
 133 {
 134     void **ptr= (void**)arg;
 135     av_free(*ptr);
 136     *ptr = NULL;
 137 }
 138
 139 void *av_mallocz(unsigned int size)
 140 {
 141     void *ptr = av_malloc(size);
 142     if (ptr)
 143         memset(ptr, 0, size);
 144     return ptr;
 145 }
 146
 147 char *av_strdup(const char *s)
 148 {
 149     char *ptr= NULL;
 150     if(s){
 151         int len = strlen(s) + 1;
 152         ptr = av_malloc(len);
 153         if (ptr)
 154             memcpy(ptr, s, len);
 155     }
 156     return ptr;
 157 }
 158