140 lines
3.7 KiB
C++
140 lines
3.7 KiB
C++
/*
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* Copyright (c) 2010 The WebM project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef VPX_DSP_BITREADER_H_
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#define VPX_DSP_BITREADER_H_
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#include <stddef.h>
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#include <limits.h>
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#include "./vpx_config.h"
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#include "vpx_ports/mem.h"
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#include "vpx/vp8dx.h"
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#include "vpx/vpx_integer.h"
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#include "vpx_dsp/prob.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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typedef size_t BD_VALUE;
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#define BD_VALUE_SIZE ((int)sizeof(BD_VALUE) * CHAR_BIT)
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// This is meant to be a large, positive constant that can still be efficiently
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// loaded as an immediate (on platforms like ARM, for example).
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// Even relatively modest values like 100 would work fine.
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#define LOTS_OF_BITS 0x40000000
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typedef struct {
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// Be careful when reordering this struct, it may impact the cache negatively.
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BD_VALUE value;
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unsigned int range;
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int count;
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const uint8_t *buffer_end;
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const uint8_t *buffer;
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vpx_decrypt_cb decrypt_cb;
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void *decrypt_state;
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uint8_t clear_buffer[sizeof(BD_VALUE) + 1];
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} vpx_reader;
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int vpx_reader_init(vpx_reader *r,
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const uint8_t *buffer,
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size_t size,
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vpx_decrypt_cb decrypt_cb,
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void *decrypt_state);
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void vpx_reader_fill(vpx_reader *r);
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const uint8_t *vpx_reader_find_end(vpx_reader *r);
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static INLINE int vpx_reader_has_error(vpx_reader *r) {
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// Check if we have reached the end of the buffer.
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//
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// Variable 'count' stores the number of bits in the 'value' buffer, minus
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// 8. The top byte is part of the algorithm, and the remainder is buffered
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// to be shifted into it. So if count == 8, the top 16 bits of 'value' are
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// occupied, 8 for the algorithm and 8 in the buffer.
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//
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// When reading a byte from the user's buffer, count is filled with 8 and
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// one byte is filled into the value buffer. When we reach the end of the
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// data, count is additionally filled with LOTS_OF_BITS. So when
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// count == LOTS_OF_BITS - 1, the user's data has been exhausted.
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//
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// 1 if we have tried to decode bits after the end of stream was encountered.
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// 0 No error.
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return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS;
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}
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static INLINE int vpx_read(vpx_reader *r, int prob) {
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unsigned int bit = 0;
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BD_VALUE value;
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BD_VALUE bigsplit;
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int count;
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unsigned int range;
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unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
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if (r->count < 0)
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vpx_reader_fill(r);
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value = r->value;
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count = r->count;
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bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT);
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range = split;
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if (value >= bigsplit) {
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range = r->range - split;
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value = value - bigsplit;
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bit = 1;
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}
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{
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register int shift = vpx_norm[range];
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range <<= shift;
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value <<= shift;
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count -= shift;
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}
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r->value = value;
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r->count = count;
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r->range = range;
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return bit;
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}
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static INLINE int vpx_read_bit(vpx_reader *r) {
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return vpx_read(r, 128); // vpx_prob_half
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}
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static INLINE int vpx_read_literal(vpx_reader *r, int bits) {
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int literal = 0, bit;
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for (bit = bits - 1; bit >= 0; bit--)
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literal |= vpx_read_bit(r) << bit;
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return literal;
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}
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static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree,
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const vpx_prob *probs) {
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vpx_tree_index i = 0;
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while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0)
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continue;
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return -i;
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}
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif // VPX_DSP_BITREADER_H_
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