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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 LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef VP9_DECODER_VP9_DBOOLHUFF_H_
#define VP9_DECODER_VP9_DBOOLHUFF_H_
#include <stddef.h>
#include <limits.h>
#include "./vpx_config.h"
#include "vpx_ports/mem.h"
#include "vpx/vpx_integer.h"
typedef size_t VP9_BD_VALUE;
#define VP9_BD_VALUE_SIZE ((int)sizeof(VP9_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 VP9_LOTS_OF_BITS (0x40000000)
typedef struct {
const unsigned char *user_buffer_end;
const unsigned char *user_buffer;
VP9_BD_VALUE value;
int count;
unsigned int range;
} BOOL_DECODER;
DECLARE_ALIGNED(16, extern const uint8_t, vp9_norm[256]);
int vp9_start_decode(BOOL_DECODER *br,
const unsigned char *source,
unsigned int source_sz);
void vp9_bool_decoder_fill(BOOL_DECODER *br);
int vp9_decode_uniform(BOOL_DECODER *br, int n);
int vp9_decode_term_subexp(BOOL_DECODER *br, int k, int num_syms);
int vp9_inv_recenter_nonneg(int v, int m);
static int decode_bool(BOOL_DECODER *br, int probability) {
unsigned int bit = 0;
VP9_BD_VALUE value;
VP9_BD_VALUE bigsplit;
int count;
unsigned int range;
unsigned int split = 1 + (((br->range - 1) * probability) >> 8);
if (br->count < 0)
vp9_bool_decoder_fill(br);
value = br->value;
count = br->count;
bigsplit = (VP9_BD_VALUE)split << (VP9_BD_VALUE_SIZE - 8);
range = split;
if (value >= bigsplit) {
range = br->range - split;
value = value - bigsplit;
bit = 1;
}
{
register unsigned int shift = vp9_norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
br->value = value;
br->count = count;
br->range = range;
return bit;
}
static int decode_value(BOOL_DECODER *br, int bits) {
int z = 0;
int bit;
for (bit = bits - 1; bit >= 0; bit--) {
z |= decode_bool(br, 0x80) << bit;
}
return z;
}
static int 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 VP9_LOTS_OF_BITS. So when
// count == VP9_LOTS_OF_BITS - 1, the user's data has been exhausted.
//
// 1 if we have tried to decode bits after the end of stream was encountered.
// 0 No error.
return br->count > VP9_BD_VALUE_SIZE && br->count < VP9_LOTS_OF_BITS;
}
int vp9_decode_unsigned_max(BOOL_DECODER *br, int max);
#endif // VP9_DECODER_VP9_DBOOLHUFF_H_
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