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/vpx_integer.h" 21 22 #ifdef __cplusplus 23 extern "C" { 24 #endif 25 26 typedef size_t VP8_BD_VALUE; 27 28 #define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE)*CHAR_BIT) 29 30 /*This is meant to be a large, positive constant that can still be efficiently 31 loaded as an immediate (on platforms like ARM, for example). 32 Even relatively modest values like 100 would work fine.*/ 33 #define VP8_LOTS_OF_BITS (0x40000000) 34 35 /*Decrypt n bytes of data from input -> output, using the decrypt_state 36 passed in VP8D_SET_DECRYPTOR. 37 */ 38 typedef void (vp8_decrypt_cb)(void *decrypt_state, const unsigned char *input, 39 unsigned char *output, int count); 40 41 typedef struct 42 { 43 const unsigned char *user_buffer_end; 44 const unsigned char *user_buffer; 45 VP8_BD_VALUE value; 46 int count; 47 unsigned int range; 48 vp8_decrypt_cb *decrypt_cb; 49 void *decrypt_state; 50 } BOOL_DECODER; 51 52 DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]); 53 54 int vp8dx_start_decode(BOOL_DECODER *br, 55 const unsigned char *source, 56 unsigned int source_sz, 57 vp8_decrypt_cb *decrypt_cb, 58 void *decrypt_state); 59 60 void vp8dx_bool_decoder_fill(BOOL_DECODER *br); 61 62 63 static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) { 64 unsigned int bit = 0; 65 VP8_BD_VALUE value; 66 unsigned int split; 67 VP8_BD_VALUE bigsplit; 68 int count; 69 unsigned int range; 70 71 split = 1 + (((br->range - 1) * probability) >> 8); 72 73 if(br->count < 0) 74 vp8dx_bool_decoder_fill(br); 75 76 value = br->value; 77 count = br->count; 78 79 bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8); 80 81 range = split; 82 83 if (value >= bigsplit) 84 { 85 range = br->range - split; 86 value = value - bigsplit; 87 bit = 1; 88 } 89 90 { 91 register unsigned int shift = vp8_norm[range]; 92 range <<= shift; 93 value <<= shift; 94 count -= shift; 95 } 96 br->value = value; 97 br->count = count; 98 br->range = range; 99 100 return bit; 101 } 102 103 static int vp8_decode_value(BOOL_DECODER *br, int bits) 104 { 105 int z = 0; 106 int bit; 107 108 for (bit = bits - 1; bit >= 0; bit--) 109 { 110 z |= (vp8dx_decode_bool(br, 0x80) << bit); 111 } 112 113 return z; 114 } 115 116 static int vp8dx_bool_error(BOOL_DECODER *br) 117 { 118 /* Check if we have reached the end of the buffer. 119 * 120 * Variable 'count' stores the number of bits in the 'value' buffer, minus 121 * 8. The top byte is part of the algorithm, and the remainder is buffered 122 * to be shifted into it. So if count == 8, the top 16 bits of 'value' are 123 * occupied, 8 for the algorithm and 8 in the buffer. 124 * 125 * When reading a byte from the user's buffer, count is filled with 8 and 126 * one byte is filled into the value buffer. When we reach the end of the 127 * data, count is additionally filled with VP8_LOTS_OF_BITS. So when 128 * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted. 129 */ 130 if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS)) 131 { 132 /* We have tried to decode bits after the end of 133 * stream was encountered. 134 */ 135 return 1; 136 } 137 138 /* No error. */ 139 return 0; 140 } 141 142 #ifdef __cplusplus 143 } // extern "C" 144 #endif 145 146 #endif // VP8_DECODER_DBOOLHUFF_H_ 147
