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 12#ifndef VP8_DECODER_DBOOLHUFF_H_ 13#define VP8_DECODER_DBOOLHUFF_H_ 14 15#include <stddef.h> 16#include <limits.h> 17 18#include "vpx_config.h" 19#include "vpx_ports/mem.h" 20#include "vpx/vp8dx.h" 21#include "vpx/vpx_integer.h" 22 23#ifdef __cplusplus 24extern "C" { 25#endif 26 27typedef size_t VP8_BD_VALUE; 28 29#define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_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 VP8_LOTS_OF_BITS (0x40000000) 35 36typedef struct 37{ 38 const unsigned char *user_buffer_end; 39 const unsigned char *user_buffer; 40 VP8_BD_VALUE value; 41 int count; 42 unsigned int range; 43 vpx_decrypt_cb decrypt_cb; 44 void *decrypt_state; 45} BOOL_DECODER; 46 47DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]); 48 49int vp8dx_start_decode(BOOL_DECODER *br, 50 const unsigned char *source, 51 unsigned int source_sz, 52 vpx_decrypt_cb decrypt_cb, 53 void *decrypt_state); 54 55void vp8dx_bool_decoder_fill(BOOL_DECODER *br); 56 57 58static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) { 59 unsigned int bit = 0; 60 VP8_BD_VALUE value; 61 unsigned int split; 62 VP8_BD_VALUE bigsplit; 63 int count; 64 unsigned int range; 65 66 split = 1 + (((br->range - 1) * probability) >> 8); 67 68 if(br->count < 0) 69 vp8dx_bool_decoder_fill(br); 70 71 value = br->value; 72 count = br->count; 73 74 bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8); 75 76 range = split; 77 78 if (value >= bigsplit) 79 { 80 range = br->range - split; 81 value = value - bigsplit; 82 bit = 1; 83 } 84 85 { 86 register unsigned int shift = vp8_norm[range]; 87 range <<= shift; 88 value <<= shift; 89 count -= shift; 90 } 91 br->value = value; 92 br->count = count; 93 br->range = range; 94 95 return bit; 96} 97 98static int vp8_decode_value(BOOL_DECODER *br, int bits) 99{ 100 int z = 0; 101 int bit; 102 103 for (bit = bits - 1; bit >= 0; bit--) 104 { 105 z |= (vp8dx_decode_bool(br, 0x80) << bit); 106 } 107 108 return z; 109} 110 111static int vp8dx_bool_error(BOOL_DECODER *br) 112{ 113 /* Check if we have reached the end of the buffer. 114 * 115 * Variable 'count' stores the number of bits in the 'value' buffer, minus 116 * 8. The top byte is part of the algorithm, and the remainder is buffered 117 * to be shifted into it. So if count == 8, the top 16 bits of 'value' are 118 * occupied, 8 for the algorithm and 8 in the buffer. 119 * 120 * When reading a byte from the user's buffer, count is filled with 8 and 121 * one byte is filled into the value buffer. When we reach the end of the 122 * data, count is additionally filled with VP8_LOTS_OF_BITS. So when 123 * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted. 124 */ 125 if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS)) 126 { 127 /* We have tried to decode bits after the end of 128 * stream was encountered. 129 */ 130 return 1; 131 } 132 133 /* No error. */ 134 return 0; 135} 136 137#ifdef __cplusplus 138} // extern "C" 139#endif 140 141#endif // VP8_DECODER_DBOOLHUFF_H_ 142