mirror of
https://github.com/google/brotli.git
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177 lines
6.0 KiB
C
177 lines
6.0 KiB
C
/* Copyright 2013 Google Inc. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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Bit reading helpers
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*/
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#ifndef BROTLI_DEC_BIT_READER_H_
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#define BROTLI_DEC_BIT_READER_H_
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#include <string.h>
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#include "./streams.h"
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#include "./types.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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#define BROTLI_MAX_NUM_BIT_READ 25
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#define BROTLI_READ_SIZE 4096
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#define BROTLI_IBUF_SIZE (2 * BROTLI_READ_SIZE + 32)
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#define BROTLI_IBUF_MASK (2 * BROTLI_READ_SIZE - 1)
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#define UNALIGNED_COPY64(dst, src) memcpy(dst, src, 8)
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#define UNALIGNED_MOVE64(dst, src) memmove(dst, src, 8)
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static const uint32_t kBitMask[BROTLI_MAX_NUM_BIT_READ] = {
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0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767,
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65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215
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};
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typedef struct {
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/* Input byte buffer, consist of a ringbuffer and a "slack" region where */
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/* bytes from the start of the ringbuffer are copied. */
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uint8_t buf_[BROTLI_IBUF_SIZE];
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uint8_t* buf_ptr_; /* next input will write here */
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BrotliInput input_; /* input callback */
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uint64_t val_; /* pre-fetched bits */
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uint32_t pos_; /* byte position in stream */
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uint32_t bit_pos_; /* current bit-reading position in val_ */
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uint32_t bit_end_pos_; /* bit-reading end position from LSB of val_ */
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int eos_; /* input stream is finished */
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} BrotliBitReader;
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int BrotliInitBitReader(BrotliBitReader* const br, BrotliInput input);
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/* Return the prefetched bits, so they can be looked up. */
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static BROTLI_INLINE uint32_t BrotliPrefetchBits(BrotliBitReader* const br) {
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return (uint32_t)(br->val_ >> br->bit_pos_);
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}
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/* For jumping over a number of bits in the bit stream when accessed with */
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/* BrotliPrefetchBits and BrotliFillBitWindow. */
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static BROTLI_INLINE void BrotliSetBitPos(BrotliBitReader* const br,
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uint32_t val) {
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#ifdef BROTLI_DECODE_DEBUG
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uint32_t n_bits = val - br->bit_pos_;
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const uint32_t bval = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
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printf("[BrotliReadBits] %010d %2d val: %6x\n",
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(br->pos_ << 3) + br->bit_pos_ - 64, n_bits, bval);
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#endif
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br->bit_pos_ = val;
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}
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/* Reload up to 64 bits byte-by-byte */
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static BROTLI_INLINE void ShiftBytes(BrotliBitReader* const br) {
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while (br->bit_pos_ >= 8) {
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br->val_ >>= 8;
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br->val_ |= ((uint64_t)br->buf_[br->pos_ & BROTLI_IBUF_MASK]) << 56;
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++br->pos_;
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br->bit_pos_ -= 8;
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br->bit_end_pos_ -= 8;
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}
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}
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/* Fills up the input ringbuffer by calling the input callback.
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Does nothing if there are at least 32 bytes present after current position.
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Returns 0 if either:
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- the input callback returned an error, or
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- there is no more input and the position is past the end of the stream.
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After encountering the end of the input stream, 32 additional zero bytes are
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copied to the ringbuffer, therefore it is safe to call this function after
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every 32 bytes of input is read.
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*/
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static BROTLI_INLINE int BrotliReadMoreInput(BrotliBitReader* const br) {
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if (br->bit_end_pos_ > 256) {
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return 1;
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} else if (br->eos_) {
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return br->bit_pos_ <= br->bit_end_pos_;
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} else {
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uint8_t* dst = br->buf_ptr_;
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int bytes_read = BrotliRead(br->input_, dst, BROTLI_READ_SIZE);
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if (bytes_read < 0) {
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return 0;
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}
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if (bytes_read < BROTLI_READ_SIZE) {
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br->eos_ = 1;
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/* Store 32 bytes of zero after the stream end. */
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#if (defined(__x86_64__) || defined(_M_X64))
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*(uint64_t*)(dst + bytes_read) = 0;
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*(uint64_t*)(dst + bytes_read + 8) = 0;
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*(uint64_t*)(dst + bytes_read + 16) = 0;
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*(uint64_t*)(dst + bytes_read + 24) = 0;
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#else
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memset(dst + bytes_read, 0, 32);
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#endif
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}
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if (dst == br->buf_) {
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/* Copy the head of the ringbuffer to the slack region. */
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#if (defined(__x86_64__) || defined(_M_X64))
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UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 32, br->buf_);
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UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 24, br->buf_ + 8);
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UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 16, br->buf_ + 16);
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UNALIGNED_COPY64(br->buf_ + BROTLI_IBUF_SIZE - 8, br->buf_ + 24);
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#else
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memcpy(br->buf_ + (BROTLI_READ_SIZE << 1), br->buf_, 32);
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#endif
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br->buf_ptr_ = br->buf_ + BROTLI_READ_SIZE;
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} else {
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br->buf_ptr_ = br->buf_;
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}
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br->bit_end_pos_ += ((uint32_t)bytes_read << 3);
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return 1;
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}
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}
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/* Advances the Read buffer by 5 bytes to make room for reading next 24 bits. */
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static BROTLI_INLINE void BrotliFillBitWindow(BrotliBitReader* const br) {
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if (br->bit_pos_ >= 40) {
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#if (defined(__x86_64__) || defined(_M_X64))
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br->val_ >>= 40;
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/* The expression below needs a little-endian arch to work correctly. */
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/* This gives a large speedup for decoding speed. */
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br->val_ |= *(const uint64_t*)(
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br->buf_ + (br->pos_ & BROTLI_IBUF_MASK)) << 24;
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br->pos_ += 5;
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br->bit_pos_ -= 40;
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br->bit_end_pos_ -= 40;
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#else
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ShiftBytes(br);
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#endif
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}
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}
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/* Reads the specified number of bits from Read Buffer. */
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static BROTLI_INLINE uint32_t BrotliReadBits(
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BrotliBitReader* const br, int n_bits) {
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uint32_t val;
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BrotliFillBitWindow(br);
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val = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
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#ifdef BROTLI_DECODE_DEBUG
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printf("[BrotliReadBits] %010d %2d val: %6x\n",
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(br->pos_ << 3) + br->bit_pos_ - 64, n_bits, val);
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#endif
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br->bit_pos_ += (uint32_t)n_bits;
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return val;
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}
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#if defined(__cplusplus) || defined(c_plusplus)
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} /* extern "C" */
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#endif
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#endif /* BROTLI_DEC_BIT_READER_H_ */
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