115 lines
3.1 KiB
C
115 lines
3.1 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 VP9_DECODER_VP9_DBOOLHUFF_H_
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#define VP9_DECODER_VP9_DBOOLHUFF_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/vpx_integer.h"
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typedef size_t VP9_BD_VALUE;
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#define VP9_BD_VALUE_SIZE ((int)sizeof(VP9_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 VP9_LOTS_OF_BITS 0x40000000
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typedef struct {
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const uint8_t *buffer_end;
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const uint8_t *buffer;
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VP9_BD_VALUE value;
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int count;
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unsigned int range;
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} vp9_reader;
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DECLARE_ALIGNED(16, extern const uint8_t, vp9_norm[256]);
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int vp9_reader_init(vp9_reader *r, const uint8_t *buffer, size_t size);
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void vp9_reader_fill(vp9_reader *r);
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const uint8_t *vp9_reader_find_end(vp9_reader *r);
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static int vp9_read(vp9_reader *br, int probability) {
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unsigned int bit = 0;
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VP9_BD_VALUE value;
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VP9_BD_VALUE bigsplit;
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int count;
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unsigned int range;
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unsigned int split = 1 + (((br->range - 1) * probability) >> 8);
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if (br->count < 0)
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vp9_reader_fill(br);
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value = br->value;
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count = br->count;
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bigsplit = (VP9_BD_VALUE)split << (VP9_BD_VALUE_SIZE - 8);
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range = split;
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if (value >= bigsplit) {
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range = br->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 unsigned int shift = vp9_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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br->value = value;
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br->count = count;
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br->range = range;
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return bit;
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}
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static int vp9_read_bit(vp9_reader *r) {
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return vp9_read(r, 128); // vp9_prob_half
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}
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static int vp9_read_literal(vp9_reader *br, int bits) {
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int z = 0, bit;
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for (bit = bits - 1; bit >= 0; bit--)
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z |= vp9_read_bit(br) << bit;
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return z;
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}
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static int vp9_reader_has_error(vp9_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 VP9_LOTS_OF_BITS. So when
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// count == VP9_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 > VP9_BD_VALUE_SIZE && r->count < VP9_LOTS_OF_BITS;
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}
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#endif // VP9_DECODER_VP9_DBOOLHUFF_H_
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