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ffmpeg / libavcodec / mem.c @ 5509bffa

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/*
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 * default memory allocator for libavcodec
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 * Copyright (c) 2002 Fabrice Bellard.
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 *
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 * This library is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2 of the License, or (at your option) any later version.
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 *
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 * This library is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with this library; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/**
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 * @file mem.c
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 * default memory allocator for libavcodec.
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 */
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#include "avcodec.h"
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/* here we can use OS dependant allocation functions */
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#undef malloc
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#undef free
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#undef realloc
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#ifdef HAVE_MALLOC_H
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#include <malloc.h>
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#endif
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/* you can redefine av_malloc and av_free in your project to use your
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   memory allocator. You do not need to suppress this file because the
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   linker will do it automatically */
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/**
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 * Memory allocation of size byte with alignment suitable for all
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 * memory accesses (including vectors if available on the
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 * CPU). av_malloc(0) must return a non NULL pointer.
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 */
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void *av_malloc(unsigned int size)
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{
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    void *ptr;
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#ifdef MEMALIGN_HACK
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    int diff;
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#endif
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    /* lets disallow possible ambiguous cases */
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    if(size > INT_MAX)
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        return NULL;
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#ifdef MEMALIGN_HACK
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    ptr = malloc(size+16+1);
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    diff= ((-(int)ptr - 1)&15) + 1;
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    ptr += diff;
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    ((char*)ptr)[-1]= diff;
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#elif defined (HAVE_MEMALIGN)
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    ptr = memalign(16,size);
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    /* Why 64?
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       Indeed, we should align it:
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         on 4 for 386
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         on 16 for 486
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         on 32 for 586, PPro - k6-III
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         on 64 for K7 (maybe for P3 too).
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       Because L1 and L2 caches are aligned on those values.
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       But I don't want to code such logic here!
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     */
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     /* Why 16?
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        because some cpus need alignment, for example SSE2 on P4, & most RISC cpus
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        it will just trigger an exception and the unaligned load will be done in the
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        exception handler or it will just segfault (SSE2 on P4)
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        Why not larger? because i didnt see a difference in benchmarks ...
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     */
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     /* benchmarks with p3
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        memalign(64)+1          3071,3051,3032
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        memalign(64)+2          3051,3032,3041
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        memalign(64)+4          2911,2896,2915
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        memalign(64)+8          2545,2554,2550
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        memalign(64)+16         2543,2572,2563
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        memalign(64)+32         2546,2545,2571
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        memalign(64)+64         2570,2533,2558
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        btw, malloc seems to do 8 byte alignment by default here
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     */
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#else
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    ptr = malloc(size);
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#endif
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    return ptr;
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}
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/**
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 * av_realloc semantics (same as glibc): if ptr is NULL and size > 0,
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 * identical to malloc(size). If size is zero, it is identical to
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 * free(ptr) and NULL is returned.
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 */
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void *av_realloc(void *ptr, unsigned int size)
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{
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#ifdef MEMALIGN_HACK
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    int diff;
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#endif
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    /* lets disallow possible ambiguous cases */
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    if(size > INT_MAX)
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        return NULL;
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#ifdef MEMALIGN_HACK
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    //FIXME this isnt aligned correctly though it probably isnt needed
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    if(!ptr) return av_malloc(size);
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    diff= ((char*)ptr)[-1];
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    return realloc(ptr - diff, size + diff) + diff;
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#else
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    return realloc(ptr, size);
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#endif
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}
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/**
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 * Free memory which has been allocated with av_malloc(z)() or av_realloc().
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 * NOTE: ptr = NULL is explicetly allowed 
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 * Note2: it is recommanded that you use av_freep() instead
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 */
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void av_free(void *ptr)
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{
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    /* XXX: this test should not be needed on most libcs */
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    if (ptr)
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#ifdef MEMALIGN_HACK
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        free(ptr - ((char*)ptr)[-1]);
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#else
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        free(ptr);
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#endif
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}
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