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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 uint8_t *buffer_end;
const uint8_t *buffer;
VP9_BD_VALUE value;
int count;
unsigned int range;
} vp9_reader;
DECLARE_ALIGNED(16, extern const uint8_t, vp9_norm[256]);
int vp9_reader_init(vp9_reader *r, const uint8_t *buffer, size_t size);
void vp9_reader_fill(vp9_reader *r);
const uint8_t *vp9_reader_find_end(vp9_reader *r);
static int vp9_read(vp9_reader *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_reader_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 vp9_read_bit(vp9_reader *r) {
return vp9_read(r, 128); // vp9_prob_half
}
static int vp9_read_literal(vp9_reader *br, int bits) {
int z = 0, bit;
for (bit = bits - 1; bit >= 0; bit--)
z |= vp9_read_bit(br) << bit;
return z;
}
static int vp9_reader_has_error(vp9_reader *r) {
// 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 r->count > VP9_BD_VALUE_SIZE && r->count < VP9_LOTS_OF_BITS;
}
#endif // VP9_DECODER_VP9_DBOOLHUFF_H_
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