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a949360163
need for 1 more extra byte. * Checking whether the to be allocated size is larger than INT_MAX, doesn't assure that size+16 bytes for the MEMALIGN_HACK isn't larger than INT_MAX. * malloc might return NULL. Checking for it before using that pointer seems like a good idea. Patch by Herve W. H PPP O PPP W PPP aka PPP V+ffmpeg AH gmail PPP com Original thread: Date: Jun 29, 2006 1:21 PM Subject: [Ffmpeg-devel] [PATCH] minor improvements to libavcodec/mem.c Originally committed as revision 5559 to svn://svn.ffmpeg.org/ffmpeg/trunk
138 lines
3.9 KiB
C
138 lines
3.9 KiB
C
/*
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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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long diff;
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#endif
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/* let's disallow possible ambiguous cases */
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if(size > (INT_MAX-16) )
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return NULL;
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#ifdef MEMALIGN_HACK
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ptr = malloc(size+16);
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if(!ptr)
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return ptr;
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diff= ((-(long)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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/* let's disallow possible ambiguous cases */
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if(size > (INT_MAX-16) )
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return NULL;
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#ifdef MEMALIGN_HACK
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//FIXME this isn't aligned correctly, though it probably isn't 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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