Commit 23510de8 authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont
Browse files

block_Realloc: optimize and conformize

 * Shrink the buffer in either direction before reallocating,
   so we don't need to copy discarded data.
(* Special case if the payload is entirely discarded.)
 * Avoid potentially overflowing pointer comparisons
  (In real life, it works, but it is not defined by the C specification).
parent 8152b0d8
......@@ -2,7 +2,7 @@
* block.c: Data blocks management functions
*****************************************************************************
* Copyright (C) 2003-2004 the VideoLAN team
* $Id$
* Copyright (C) 2007-2009 Rémi Denis-Courmont
*
* Authors: Laurent Aimar <fenrir@videolan.org>
*
......@@ -30,6 +30,7 @@
#include <vlc_common.h>
#include <sys/stat.h>
#include <assert.h>
#include "vlc_block.h"
/**
......@@ -111,9 +112,10 @@ block_t *block_Alloc( size_t i_size )
block_t *block_Realloc( block_t *p_block, ssize_t i_prebody, size_t i_body )
{
block_sys_t *p_sys = (block_sys_t *)p_block;
ssize_t i_buffer_size = i_prebody + i_body;
size_t requested = i_prebody + i_body;
if( i_buffer_size <= 0 )
/* Corner case: empty block requested */
if( i_prebody <= 0 && i_body <= (size_t)(-i_prebody) )
{
block_Release( p_block );
return NULL;
......@@ -132,30 +134,56 @@ block_t *block_Realloc( block_t *p_block, ssize_t i_prebody, size_t i_body )
p_sys = (block_sys_t *)p_block;
}
/* Adjust reserved header if there is enough room */
if( p_block->p_buffer - i_prebody > p_sys->p_allocated_buffer &&
p_block->p_buffer - i_prebody < p_sys->p_allocated_buffer +
p_sys->i_allocated_buffer )
uint8_t *p_start = p_sys->p_allocated_buffer;
uint8_t *p_end = p_sys->p_allocated_buffer + p_sys->i_allocated_buffer;
assert( p_block->p_buffer + p_block->i_buffer <= p_end );
assert( p_block->p_buffer >= p_start );
/* Corner case: the current payload is discarded completely */
if( i_prebody <= 0 && p_block->i_buffer <= (size_t)-i_prebody )
p_block->i_buffer = 0; /* discard current payload */
if( p_block->i_buffer == 0 )
{
size_t available = p_end - p_start;
if( requested <= available )
{ /* Enough room: recycle buffer */
size_t extra = available - requested;
p_block->p_buffer = p_start + (extra / 2);
p_block->i_buffer = requested;
return p_block;
}
/* Not enough room: allocate a new buffer */
block_Release( p_block );
return block_Alloc( requested );
}
/* First, shrink payload */
/* Pull payload start */
if( i_prebody < 0 )
{
assert( p_block->i_buffer >= (size_t)-i_prebody );
p_block->p_buffer -= i_prebody;
p_block->i_buffer += i_prebody;
i_body += i_prebody;
i_prebody = 0;
}
/* Adjust payload size if there is enough room */
if( p_block->p_buffer + i_body < p_sys->p_allocated_buffer +
p_sys->i_allocated_buffer )
{
p_block->i_buffer = i_buffer_size;
i_body = 0;
}
/* Trim payload end */
if( p_block->i_buffer > i_body )
p_block->i_buffer = i_body;
/* Not enough room, reallocate the buffer */
if( i_body > 0 || i_prebody > 0 )
/* Second, reallocate the buffer if we lack space. This is done now to
* minimize the payload size for memory copy. */
assert( i_prebody >= 0 );
if( (size_t)(p_block->p_buffer - p_start) < (size_t)i_prebody
|| (size_t)(p_end - p_block->p_buffer) < p_block->i_buffer + i_body )
{
/* FIXME: this is really dumb, we should use realloc() */
block_t *p_rea = block_New( NULL, i_buffer_size );
block_t *p_rea = block_Alloc( requested );
if( p_rea )
{
p_rea->i_dts = p_block->i_dts;
......@@ -164,18 +192,31 @@ block_t *block_Realloc( block_t *p_block, ssize_t i_prebody, size_t i_body )
p_rea->i_length = p_block->i_length;
p_rea->i_rate = p_block->i_rate;
p_rea->i_samples = p_block->i_samples;
memcpy( p_rea->p_buffer + i_prebody, p_block->p_buffer,
__MIN( p_block->i_buffer, p_rea->i_buffer - i_prebody ) );
p_rea->p_buffer += i_prebody;
p_rea->i_buffer -= i_prebody;
memcpy( p_rea->p_buffer, p_block->p_buffer, p_block->i_buffer );
}
block_Release( p_block );
p_block = p_rea;
}
/* NOTE: p_start and p_end are corrupted from this point */
/* Third, expand payload */
return p_rea;
/* Push payload start */
if( i_prebody > 0 )
{
p_block->p_buffer -= i_prebody;
p_block->i_buffer += i_prebody;
i_body += i_prebody;
i_prebody = 0;
}
/* Expand payload to requested size */
p_block->i_buffer = i_body;
/* We have a very large reserved footer now? Release some of it.
* XXX it may not keep the algniment of p_buffer */
* XXX it might not preserve the alignment of p_buffer */
if( (p_sys->p_allocated_buffer + p_sys->i_allocated_buffer) -
(p_block->p_buffer + p_block->i_buffer) > BLOCK_WASTE_SIZE )
{
......
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