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 mem.c
  24  * default memory allocator for libavutil.
  25  */
  26
  27 #include "config.h"
  28 #include "common.h"
  29
  30 /* here we can use OS dependent allocation functions */
  31 #undef malloc
  32 #undef free
  33 #undef realloc
  34
  35 #include <limits.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #if HAVE_MALLOC_H
  39 #include <malloc.h>
  40 #endif
  41
  42 /* you can redefine av_malloc and av_free in your project to use your
  43    memory allocator. You do not need to suppress this file because the
  44    linker will do it automatically */
  45
  46 void *av_malloc(unsigned int size)
  47 {
  48     void *ptr = NULL;
  49 #if CONFIG_MEMALIGN_HACK
  50     long diff;
  51 #endif
  52
  53     /* let's disallow possible ambiguous cases */
  54     if(size > (INT_MAX-16) )
  55         return NULL;
  56
  57 #if CONFIG_MEMALIGN_HACK
  58     ptr = malloc(size+16);
  59     if(!ptr)
  60         return ptr;
  61     diff= ((-(long)ptr - 1)&15) + 1;
  62     ptr = (char*)ptr + diff;
  63     ((char*)ptr)[-1]= diff;
  64 #elif HAVE_POSIX_MEMALIGN
  65     posix_memalign(&ptr,16,size);
  66 #elif HAVE_MEMALIGN
  67     ptr = memalign(16,size);
  68     /* Why 64?
  69        Indeed, we should align it:
  70          on 4 for 386
  71          on 16 for 486
  72          on 32 for 586, PPro - k6-III
  73          on 64 for K7 (maybe for P3 too).
  74        Because L1 and L2 caches are aligned on those values.
  75        But I don't want to code such logic here!
  76      */
  77      /* Why 16?
  78         Because some CPUs need alignment, for example SSE2 on P4, & most RISC CPUs
  79         it will just trigger an exception and the unaligned load will be done in the
  80         exception handler or it will just segfault (SSE2 on P4)
  81         Why not larger? Because I did not see a difference in benchmarks ...
  82      */
  83      /* benchmarks with p3
  84         memalign(64)+1          3071,3051,3032
  85         memalign(64)+2          3051,3032,3041
  86         memalign(64)+4          2911,2896,2915
  87         memalign(64)+8          2545,2554,2550
  88         memalign(64)+16         2543,2572,2563
  89         memalign(64)+32         2546,2545,2571
  90         memalign(64)+64         2570,2533,2558
  91
  92         btw, malloc seems to do 8 byte alignment by default here
  93      */
  94 #else
  95     ptr = malloc(size);
  96 #endif
  97     return ptr;
  98 }
  99
 100 void *av_realloc(void *ptr, unsigned int size)
 101 {
 102 #if CONFIG_MEMALIGN_HACK
 103     int diff;
 104 #endif
 105
 106     /* let's disallow possible ambiguous cases */
 107     if(size > (INT_MAX-16) )
 108         return NULL;
 109
 110 #if CONFIG_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 (char*)realloc((char*)ptr - diff, size + diff) + diff;
 115 #else
 116     return realloc(ptr, size);
 117 #endif
 118 }
 119
 120 void av_free(void *ptr)
 121 {
 122     /* XXX: this test should not be needed on most libcs */
 123     if (ptr)
 124 #if CONFIG_MEMALIGN_HACK
 125         free((char*)ptr - ((char*)ptr)[-1]);
 126 #else
 127         free(ptr);
 128 #endif
 129 }
 130
 131 void av_freep(void *arg)
 132 {
 133     void **ptr= (void**)arg;
 134     av_free(*ptr);
 135     *ptr = NULL;
 136 }
 137
 138 void *av_mallocz(unsigned int size)
 139 {
 140     void *ptr = av_malloc(size);
 141     if (ptr)
 142         memset(ptr, 0, size);
 143     return ptr;
 144 }
 145
 146 char *av_strdup(const char *s)
 147 {
 148     char *ptr= NULL;
 149     if(s){
 150         int len = strlen(s) + 1;
 151         ptr = av_malloc(len);
 152         if (ptr)
 153             memcpy(ptr, s, len);
 154     }
 155     return ptr;
 156 }
 157