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/*
* Copyright (c) 2010 The WebM project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the dboolhuff.LICENSE file in this directory.
* See the libvpx original distribution for more information,
* including patent information, and author information.
*/
#ifndef DBOOLHUFF_H
#define DBOOLHUFF_H
#include <stddef.h>
#include <limits.h>
#include <glib.h>
typedef size_t VP8_BD_VALUE;
# define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE)*CHAR_BIT)
/*This is meant to be a large, positive constant that can still be efficiently
loaded as an immediate (on platforms like ARM, for example).
Even relatively modest values like 100 would work fine.*/
# define VP8_LOTS_OF_BITS (0x40000000)
typedef struct
{
const unsigned char *user_buffer_end;
const unsigned char *user_buffer;
VP8_BD_VALUE value;
int count;
unsigned int range;
} BOOL_DECODER;
extern const unsigned char vp8_norm[256] __attribute__((aligned(16)));
int vp8dx_start_decode(BOOL_DECODER *br,
const unsigned char *source,
unsigned int source_sz);
void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
/*The refill loop is used in several places, so define it in a macro to make
sure they're all consistent.
An inline function would be cleaner, but has a significant penalty, because
multiple BOOL_DECODER fields must be modified, and the compiler is not smart
enough to eliminate the stores to those fields and the subsequent reloads
from them when inlining the function.*/
#define VP8DX_BOOL_DECODER_FILL(_count,_value,_bufptr,_bufend) \
do \
{ \
int shift = VP8_BD_VALUE_SIZE - 8 - ((_count) + 8); \
int loop_end, x; \
size_t bits_left = ((_bufend)-(_bufptr))*CHAR_BIT; \
\
x = shift + CHAR_BIT - bits_left; \
loop_end = 0; \
if(x >= 0) \
{ \
(_count) += VP8_LOTS_OF_BITS; \
loop_end = x; \
if(!bits_left) break; \
} \
while(shift >= loop_end) \
{ \
(_count) += CHAR_BIT; \
(_value) |= (VP8_BD_VALUE)*(_bufptr)++ << shift; \
shift -= CHAR_BIT; \
} \
} \
while(0) \
static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
unsigned int bit = 0;
VP8_BD_VALUE value;
unsigned int split;
VP8_BD_VALUE bigsplit;
int count;
unsigned int range;
split = 1 + (((br->range - 1) * probability) >> 8);
if(br->count < 0)
vp8dx_bool_decoder_fill(br);
value = br->value;
count = br->count;
bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
range = split;
if (value >= bigsplit)
{
range = br->range - split;
value = value - bigsplit;
bit = 1;
}
{
register unsigned int shift = vp8_norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
br->value = value;
br->count = count;
br->range = range;
return bit;
}
static G_GNUC_UNUSED int vp8_decode_value(BOOL_DECODER *br, int bits)
{
int z = 0;
int bit;
for (bit = bits - 1; bit >= 0; bit--)
{
z |= (vp8dx_decode_bool(br, 0x80) << bit);
}
return z;
}
static G_GNUC_UNUSED int vp8dx_bool_error(BOOL_DECODER *br)
{
/* Check if we have reached the end of the buffer.
*
* Variable 'count' stores the number of bits in the 'value' buffer, minus
* 8. The top byte is part of the algorithm, and the remainder is buffered
* to be shifted into it. So if count == 8, the top 16 bits of 'value' are
* occupied, 8 for the algorithm and 8 in the buffer.
*
* When reading a byte from the user's buffer, count is filled with 8 and
* one byte is filled into the value buffer. When we reach the end of the
* data, count is additionally filled with VP8_LOTS_OF_BITS. So when
* count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
*/
if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
{
/* We have tried to decode bits after the end of
* stream was encountered.
*/
return 1;
}
/* No error. */
return 0;
}
#endif
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