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 VPX_DSP_BITREADER_H_
12 #define VPX_DSP_BITREADER_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/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 vpx_reader_init(vpx_reader *r, const uint8_t *buffer, size_t size,
49 vpx_decrypt_cb decrypt_cb, void *decrypt_state);
51 void vpx_reader_fill(vpx_reader *r);
53 const uint8_t *vpx_reader_find_end(vpx_reader *r);
55 static INLINE int vpx_reader_has_error(vpx_reader *r) {
56 // Check if we have reached the end of the buffer.
58 // Variable 'count' stores the number of bits in the 'value' buffer, minus
59 // 8. The top byte is part of the algorithm, and the remainder is buffered
60 // to be shifted into it. So if count == 8, the top 16 bits of 'value' are
61 // occupied, 8 for the algorithm and 8 in the buffer.
63 // When reading a byte from the user's buffer, count is filled with 8 and
64 // one byte is filled into the value buffer. When we reach the end of the
65 // data, count is additionally filled with LOTS_OF_BITS. So when
66 // count == LOTS_OF_BITS - 1, the user's data has been exhausted.
68 // 1 if we have tried to decode bits after the end of stream was encountered.
70 return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS;
73 static INLINE int vpx_read(vpx_reader *r, int prob) {
79 unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
81 if (r->count < 0) vpx_reader_fill(r);
86 bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT);
90 if (value >= bigsplit) {
91 range = r->range - split;
92 value = value - bigsplit;
97 register int shift = vpx_norm[range];
109 static INLINE int vpx_read_bit(vpx_reader *r) {
110 return vpx_read(r, 128); // vpx_prob_half
113 static INLINE int vpx_read_literal(vpx_reader *r, int bits) {
114 int literal = 0, bit;
116 for (bit = bits - 1; bit >= 0; bit--) literal |= vpx_read_bit(r) << bit;
121 static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree,
122 const vpx_prob *probs) {
123 vpx_tree_index i = 0;
125 while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0) continue;
134 #endif // VPX_DSP_BITREADER_H_