2 * Copyright (c) 2010 The WebM project authors. All Rights Reserved.
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
11 #ifndef VP9_DECODER_VP9_READER_H_
12 #define VP9_DECODER_VP9_READER_H_
17 #include "./vpx_config.h"
18 #include "vpx_ports/mem.h"
19 #include "vpx/vp8dx.h"
20 #include "vpx/vpx_integer.h"
21 #include "vpx_dsp/vp9_prob.h"
27 typedef size_t BD_VALUE;
29 #define BD_VALUE_SIZE ((int)sizeof(BD_VALUE) * CHAR_BIT)
31 // This is meant to be a large, positive constant that can still be efficiently
32 // loaded as an immediate (on platforms like ARM, for example).
33 // Even relatively modest values like 100 would work fine.
34 #define LOTS_OF_BITS 0x40000000
37 // Be careful when reordering this struct, it may impact the cache negatively.
41 const uint8_t *buffer_end;
42 const uint8_t *buffer;
43 vpx_decrypt_cb decrypt_cb;
45 uint8_t clear_buffer[sizeof(BD_VALUE) + 1];
48 int vp9_reader_init(vp9_reader *r,
49 const uint8_t *buffer,
51 vpx_decrypt_cb decrypt_cb,
54 void vp9_reader_fill(vp9_reader *r);
56 const uint8_t *vp9_reader_find_end(vp9_reader *r);
58 static INLINE int vp9_reader_has_error(vp9_reader *r) {
59 // Check if we have reached the end of the buffer.
61 // Variable 'count' stores the number of bits in the 'value' buffer, minus
62 // 8. The top byte is part of the algorithm, and the remainder is buffered
63 // to be shifted into it. So if count == 8, the top 16 bits of 'value' are
64 // occupied, 8 for the algorithm and 8 in the buffer.
66 // When reading a byte from the user's buffer, count is filled with 8 and
67 // one byte is filled into the value buffer. When we reach the end of the
68 // data, count is additionally filled with LOTS_OF_BITS. So when
69 // count == LOTS_OF_BITS - 1, the user's data has been exhausted.
71 // 1 if we have tried to decode bits after the end of stream was encountered.
73 return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS;
76 static INLINE int vp9_read(vp9_reader *r, int prob) {
82 unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
90 bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT);
94 if (value >= bigsplit) {
95 range = r->range - split;
96 value = value - bigsplit;
101 register unsigned int shift = vp9_norm[range];
113 static INLINE int vp9_read_bit(vp9_reader *r) {
114 return vp9_read(r, 128); // vp9_prob_half
117 static INLINE int vp9_read_literal(vp9_reader *r, int bits) {
118 int literal = 0, bit;
120 for (bit = bits - 1; bit >= 0; bit--)
121 literal |= vp9_read_bit(r) << bit;
126 static INLINE int vp9_read_tree(vp9_reader *r, const vp9_tree_index *tree,
127 const vp9_prob *probs) {
128 vp9_tree_index i = 0;
130 while ((i = tree[i + vp9_read(r, probs[i >> 1])]) > 0)
140 #endif // VP9_DECODER_VP9_READER_H_