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79 lines
2.2 KiB
C
79 lines
2.2 KiB
C
/* Copyright 2013 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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/* Bit reading helpers */
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#include "bit_reader.h"
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#include <brotli/types.h>
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#include "../common/platform.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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const brotli_reg_t kBrotliBitMask[33] = { 0x00000000,
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0x00000001, 0x00000003, 0x00000007, 0x0000000F,
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0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF,
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0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF,
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0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF,
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0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF,
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0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF,
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0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF,
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0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF
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};
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void BrotliInitBitReader(BrotliBitReader* const br) {
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br->val_ = 0;
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br->bit_pos_ = 0;
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}
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BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* const br) {
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size_t aligned_read_mask = (sizeof(br->val_) >> 1) - 1;
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/* Fixing alignment after unaligned BrotliFillWindow would result accumulator
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overflow. If unalignment is caused by BrotliSafeReadBits, then there is
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enough space in accumulator to fix alignment. */
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if (BROTLI_UNALIGNED_READ_FAST) {
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aligned_read_mask = 0;
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}
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if (BrotliGetAvailableBits(br) == 0) {
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br->val_ = 0;
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if (!BrotliPullByte(br)) {
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return BROTLI_FALSE;
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}
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}
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while ((((size_t)br->next_in) & aligned_read_mask) != 0) {
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if (!BrotliPullByte(br)) {
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/* If we consumed all the input, we don't care about the alignment. */
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return BROTLI_TRUE;
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}
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}
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return BROTLI_TRUE;
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}
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BROTLI_BOOL BrotliSafeReadBits32Slow(BrotliBitReader* const br,
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brotli_reg_t n_bits, brotli_reg_t* val) {
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brotli_reg_t low_val;
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brotli_reg_t high_val;
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BrotliBitReaderState memento;
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BROTLI_DCHECK(n_bits <= 32);
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BROTLI_DCHECK(n_bits > 24);
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BrotliBitReaderSaveState(br, &memento);
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if (!BrotliSafeReadBits(br, 16, &low_val) ||
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!BrotliSafeReadBits(br, n_bits - 16, &high_val)) {
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BrotliBitReaderRestoreState(br, &memento);
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return BROTLI_FALSE;
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}
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*val = low_val | (high_val << 16);
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return BROTLI_TRUE;
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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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