1 /* Copyright 2013 Google Inc. All Rights Reserved. 2 3 Licensed under the Apache License, Version 2.0 (the "License"); 4 you may not use this file except in compliance with the License. 5 You may obtain a copy of the License at 6 7 http://www.apache.org/licenses/LICENSE-2.0 8 9 Unless required by applicable law or agreed to in writing, software 10 distributed under the License is distributed on an "AS IS" BASIS, 11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 See the License for the specific language governing permissions and 13 limitations under the License. 14 15 Bit reading helpers 16 */ 17 18 #ifndef BROTLI_DEC_BIT_READER_H_ 19 #define BROTLI_DEC_BIT_READER_H_ 20 21 #include <string.h> 22 #include "./streams.h" 23 #include "./types.h" 24 25 #if defined(__cplusplus) || defined(c_plusplus) 26 extern "C" { 27 #endif 28 29 #define BROTLI_MAX_NUM_BIT_READ 25 30 #define BROTLI_READ_SIZE 4096 31 #define BROTLI_IBUF_SIZE (2 * BROTLI_READ_SIZE + 32) 32 #define BROTLI_IBUF_MASK (2 * BROTLI_READ_SIZE - 1) 33 34 #define UNALIGNED_COPY64(dst, src) memcpy(dst, src, 8) 35 36 static const uint32_t kBitMask[BROTLI_MAX_NUM_BIT_READ] = { 37 0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767, 38 65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215 39 }; 40 41 typedef struct { 42 /* Input byte buffer, consist of a ringbuffer and a "slack" region where */ 43 /* bytes from the start of the ringbuffer are copied. */ 44 uint8_t buf_[BROTLI_IBUF_SIZE]; 45 uint8_t* buf_ptr_; /* next input will write here */ 46 BrotliInput input_; /* input callback */ 47 uint64_t val_; /* pre-fetched bits */ 48 uint32_t pos_; /* byte position in stream */ 49 uint32_t bit_pos_; /* current bit-reading position in val_ */ 50 uint32_t bit_end_pos_; /* bit-reading end position from LSB of val_ */ 51 int eos_; /* input stream is finished */ 52 } BrotliBitReader; 53 54 int BrotliInitBitReader(BrotliBitReader* const br, BrotliInput input); 55 56 /* Return the prefetched bits, so they can be looked up. */ 57 static BROTLI_INLINE uint32_t BrotliPrefetchBits(BrotliBitReader* const br) { 58 return (uint32_t)(br->val_ >> br->bit_pos_); 59 } 60 61 /* For jumping over a number of bits in the bit stream when accessed with */ 62 /* BrotliPrefetchBits and BrotliFillBitWindow. */ 63 static BROTLI_INLINE void BrotliSetBitPos(BrotliBitReader* const br, 64 uint32_t val) { 65 #ifdef BROTLI_DECODE_DEBUG 66 uint32_t n_bits = val - br->bit_pos_; 67 const uint32_t bval = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits]; 68 printf("[BrotliReadBits] %010d %2d val: %6x\n", 69 (br->pos_ << 3) + br->bit_pos_ - 64, n_bits, bval); 70 #endif 71 br->bit_pos_ = val; 72 } 73 74 /* Reload up to 64 bits byte-by-byte */ 75 static BROTLI_INLINE void ShiftBytes(BrotliBitReader* const br) { 76 while (br->bit_pos_ >= 8) { 77 br->val_ >>= 8; 78 br->val_ |= ((uint64_t)br->buf_[br->pos_ & BROTLI_IBUF_MASK]) << 56; 79 ++br->pos_; 80 br->bit_pos_ -= 8; 81 br->bit_end_pos_ -= 8; 82 } 83 } 84 85 /* Fills up the input ringbuffer by calling the input callback. 86 87 Does nothing if there are at least 32 bytes present after current position. 88 89 Returns 0 if either: 90 - the input callback returned an error, or 91 - there is no more input and the position is past the end of the stream. 92 93 After encountering the end of the input stream, 32 additional zero bytes are 94 copied to the ringbuffer, therefore it is safe to call this function after 95 every 32 bytes of input is read. 96 */ 97 static BROTLI_INLINE int BrotliReadMoreInput(BrotliBitReader* const br) { 98 if (br->bit_end_pos_ > 256) { 99 return 1; 100 } else if (br->eos_) { 101 return br->bit_pos_ <= br->bit_end_pos_; 102 } else { 103 uint8_t* dst = br->buf_ptr_; 104 int bytes_read = BrotliRead(br->input_, dst, BROTLI_READ_SIZE); 105 if (bytes_read < 0) { 106 return 0; 107 } 108 if (bytes_read < BROTLI_READ_SIZE) { 109 br->eos_ = 1; 110 /* Store 32 bytes of zero after the stream end. */ 111 #if (defined(__x86_64__) || defined(_M_X64)) 112 *(uint64_t*)(dst + bytes_read) = 0; 113 *(uint64_t*)(dst + bytes_read + 8) = 0; 114 *(uint64_t*)(dst + bytes_read + 16) = 0; 115 *(uint64_t*)(dst + bytes_read + 24) = 0; 116 #else 117 memset(dst + bytes_read, 0, 32); 118 #endif 119 } 120 if (dst == br->buf_) { 121 /* Copy the head of the ringbuffer to the slack region. */ 122 #if (defined(__x86_64__) || defined(_M_X64)) 123 UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 32, br->buf_); 124 UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 24, br->buf_ + 8); 125 UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 16, br->buf_ + 16); 126 UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 8, br->buf_ + 24); 127 #else 128 memcpy(br->buf_ + (BROTLI_READ_SIZE << 1), br->buf_, 32); 129 #endif 130 br->buf_ptr_ = br->buf_ + BROTLI_READ_SIZE; 131 } else { 132 br->buf_ptr_ = br->buf_; 133 } 134 br->bit_end_pos_ += ((uint32_t)bytes_read << 3); 135 return 1; 136 } 137 } 138 139 /* Advances the Read buffer by 5 bytes to make room for reading next 24 bits. */ 140 static BROTLI_INLINE void BrotliFillBitWindow(BrotliBitReader* const br) { 141 if (br->bit_pos_ >= 40) { 142 #if (defined(__x86_64__) || defined(_M_X64)) 143 br->val_ >>= 40; 144 /* The expression below needs a little-endian arch to work correctly. */ 145 /* This gives a large speedup for decoding speed. */ 146 br->val_ |= *(const uint64_t*)( 147 br->buf_ + (br->pos_ & BROTLI_IBUF_MASK)) << 24; 148 br->pos_ += 5; 149 br->bit_pos_ -= 40; 150 br->bit_end_pos_ -= 40; 151 #else 152 ShiftBytes(br); 153 #endif 154 } 155 } 156 157 /* Reads the specified number of bits from Read Buffer. */ 158 static BROTLI_INLINE uint32_t BrotliReadBits( 159 BrotliBitReader* const br, int n_bits) { 160 uint32_t val; 161 BrotliFillBitWindow(br); 162 val = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits]; 163 #ifdef BROTLI_DECODE_DEBUG 164 printf("[BrotliReadBits] %010d %2d val: %6x\n", 165 (br->pos_ << 3) + br->bit_pos_ - 64, n_bits, val); 166 #endif 167 br->bit_pos_ += (uint32_t)n_bits; 168 return val; 169 } 170 171 #if defined(__cplusplus) || defined(c_plusplus) 172 } /* extern "C" */ 173 #endif 174 175 #endif /* BROTLI_DEC_BIT_READER_H_ */ 176
