quicktime/ffmpeg/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 #ifdef MEMALIGN_HACK
  49     int diff;
  50 #endif
  51
  52     /* lets 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= ((-(int)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     /* lets disallow possible ambiguous cases */
 107     if(size > INT_MAX)
 108         return NULL;
 109
 110 #ifdef MEMALIGN_HACK
 111     //FIXME this isnt aligned correctly though it probably isnt 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 /* NOTE: ptr = NULL is explicetly allowed */
 121 void av_free(void *ptr)
 122 {
 123     /* XXX: this test should not be needed on most libcs */
 124     if (ptr)
 125 #ifdef MEMALIGN_HACK
 126         free(ptr - ((char*)ptr)[-1]);
 127 #else
 128         free(ptr);
 129 #endif
 130 }
 131