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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 VPX_DSP_BITREADER_H_
#define VPX_DSP_BITREADER_H_
#include <stddef.h>
#include <limits.h>
#include "./vpx_config.h"
#include "vpx_ports/mem.h"
#include "vpx/vp8dx.h"
#include "vpx/vpx_integer.h"
#include "vpx_dsp/prob.h"
#ifdef __cplusplus
extern "C" {
#endif
typedef size_t BD_VALUE;
#define BD_VALUE_SIZE ((int)sizeof(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 LOTS_OF_BITS 0x40000000
typedef struct {
// Be careful when reordering this struct, it may impact the cache negatively.
BD_VALUE value;
unsigned int range;
int count;
const uint8_t *buffer_end;
const uint8_t *buffer;
vpx_decrypt_cb decrypt_cb;
void *decrypt_state;
uint8_t clear_buffer[sizeof(BD_VALUE) + 1];
} vpx_reader;
int vpx_reader_init(vpx_reader *r,
const uint8_t *buffer,
size_t size,
vpx_decrypt_cb decrypt_cb,
void *decrypt_state);
void vpx_reader_fill(vpx_reader *r);
const uint8_t *vpx_reader_find_end(vpx_reader *r);
static INLINE int vpx_reader_has_error(vpx_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 LOTS_OF_BITS. So when
// count == 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 > BD_VALUE_SIZE && r->count < LOTS_OF_BITS;
}
static INLINE int vpx_read(vpx_reader *r, int prob) {
unsigned int bit = 0;
BD_VALUE value;
BD_VALUE bigsplit;
int count;
unsigned int range;
unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
if (r->count < 0)
vpx_reader_fill(r);
value = r->value;
count = r->count;
bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT);
range = split;
if (value >= bigsplit) {
range = r->range - split;
value = value - bigsplit;
bit = 1;
}
{
register int shift = vpx_norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
r->value = value;
r->count = count;
r->range = range;
return bit;
}
static INLINE int vpx_read_bit(vpx_reader *r) {
return vpx_read(r, 128); // vpx_prob_half
}
static INLINE int vpx_read_literal(vpx_reader *r, int bits) {
int literal = 0, bit;
for (bit = bits - 1; bit >= 0; bit--)
literal |= vpx_read_bit(r) << bit;
return literal;
}
static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree,
const vpx_prob *probs) {
vpx_tree_index i = 0;
while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0)
continue;
return -i;
}
#ifdef __cplusplus
} // extern "C"
#endif
#endif // VPX_DSP_BITREADER_H_
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