| Vignesh Venkatasubramanian | 5a9753f | 2016-01-19 11:05:09 -0800 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright (c) 2010 The WebM project authors. All Rights Reserved. |
| 3 | * |
| 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. |
| 9 | */ |
| 10 | |
| 11 | #ifndef VPX_DSP_BITREADER_H_ |
| 12 | #define VPX_DSP_BITREADER_H_ |
| 13 | |
| 14 | #include <stddef.h> |
| 15 | #include <limits.h> |
| 16 | |
| 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" |
| 22 | |
| 23 | #ifdef __cplusplus |
| 24 | extern "C" { |
| 25 | #endif |
| 26 | |
| 27 | typedef size_t BD_VALUE; |
| 28 | |
| 29 | #define BD_VALUE_SIZE ((int)sizeof(BD_VALUE) * CHAR_BIT) |
| 30 | |
| 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 |
| 35 | |
| 36 | typedef struct { |
| 37 | // Be careful when reordering this struct, it may impact the cache negatively. |
| 38 | BD_VALUE value; |
| 39 | unsigned int range; |
| 40 | int count; |
| 41 | const uint8_t *buffer_end; |
| 42 | const uint8_t *buffer; |
| 43 | vpx_decrypt_cb decrypt_cb; |
| 44 | void *decrypt_state; |
| 45 | uint8_t clear_buffer[sizeof(BD_VALUE) + 1]; |
| 46 | } vpx_reader; |
| 47 | |
| 48 | int vpx_reader_init(vpx_reader *r, |
| 49 | const uint8_t *buffer, |
| 50 | size_t size, |
| 51 | vpx_decrypt_cb decrypt_cb, |
| 52 | void *decrypt_state); |
| 53 | |
| 54 | void vpx_reader_fill(vpx_reader *r); |
| 55 | |
| 56 | const uint8_t *vpx_reader_find_end(vpx_reader *r); |
| 57 | |
| 58 | static INLINE int vpx_reader_has_error(vpx_reader *r) { |
| 59 | // Check if we have reached the end of the buffer. |
| 60 | // |
| 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. |
| 65 | // |
| 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. |
| 70 | // |
| 71 | // 1 if we have tried to decode bits after the end of stream was encountered. |
| 72 | // 0 No error. |
| 73 | return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS; |
| 74 | } |
| 75 | |
| 76 | static INLINE int vpx_read(vpx_reader *r, int prob) { |
| 77 | unsigned int bit = 0; |
| 78 | BD_VALUE value; |
| 79 | BD_VALUE bigsplit; |
| 80 | int count; |
| 81 | unsigned int range; |
| 82 | unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT; |
| 83 | |
| 84 | if (r->count < 0) |
| 85 | vpx_reader_fill(r); |
| 86 | |
| 87 | value = r->value; |
| 88 | count = r->count; |
| 89 | |
| 90 | bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT); |
| 91 | |
| 92 | range = split; |
| 93 | |
| 94 | if (value >= bigsplit) { |
| 95 | range = r->range - split; |
| 96 | value = value - bigsplit; |
| 97 | bit = 1; |
| 98 | } |
| 99 | |
| 100 | { |
| 101 | register unsigned int shift = vpx_norm[range]; |
| 102 | range <<= shift; |
| 103 | value <<= shift; |
| 104 | count -= shift; |
| 105 | } |
| 106 | r->value = value; |
| 107 | r->count = count; |
| 108 | r->range = range; |
| 109 | |
| 110 | return bit; |
| 111 | } |
| 112 | |
| 113 | static INLINE int vpx_read_bit(vpx_reader *r) { |
| 114 | return vpx_read(r, 128); // vpx_prob_half |
| 115 | } |
| 116 | |
| 117 | static INLINE int vpx_read_literal(vpx_reader *r, int bits) { |
| 118 | int literal = 0, bit; |
| 119 | |
| 120 | for (bit = bits - 1; bit >= 0; bit--) |
| 121 | literal |= vpx_read_bit(r) << bit; |
| 122 | |
| 123 | return literal; |
| 124 | } |
| 125 | |
| 126 | static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree, |
| 127 | const vpx_prob *probs) { |
| 128 | vpx_tree_index i = 0; |
| 129 | |
| 130 | while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0) |
| 131 | continue; |
| 132 | |
| 133 | return -i; |
| 134 | } |
| 135 | |
| 136 | #ifdef __cplusplus |
| 137 | } // extern "C" |
| 138 | #endif |
| 139 | |
| 140 | #endif // VPX_DSP_BITREADER_H_ |