1/* Copyright 2013 Google Inc. All Rights Reserved.
2
3 Distributed under MIT license.
4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
5*/
6
7/* Bit reading helpers */
8
9#include "bit_reader.h"
10
11#include <brotli/types.h>
12
13#include "../common/platform.h"
14
15#if defined(__cplusplus) || defined(c_plusplus)
16extern "C" {
17#endif
18
19const uint32_t kBrotliBitMask[33] = { 0x00000000,
20 0x00000001, 0x00000003, 0x00000007, 0x0000000F,
21 0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF,
22 0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF,
23 0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF,
24 0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF,
25 0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF,
26 0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF,
27 0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF
28};
29
30void BrotliInitBitReader(BrotliBitReader* const br) {
31 br->val_ = 0;
32 br->bit_pos_ = sizeof(br->val_) << 3;
33}
34
35BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* const br) {
36 size_t aligned_read_mask = (sizeof(br->val_) >> 1) - 1;
37 /* Fixing alignment after unaligned BrotliFillWindow would result accumulator
38 overflow. If unalignment is caused by BrotliSafeReadBits, then there is
39 enough space in accumulator to fix alignment. */
40 if (BROTLI_UNALIGNED_READ_FAST) {
41 aligned_read_mask = 0;
42 }
43 if (BrotliGetAvailableBits(br) == 0) {
44 if (!BrotliPullByte(br)) {
45 return BROTLI_FALSE;
46 }
47 }
48
49 while ((((size_t)br->next_in) & aligned_read_mask) != 0) {
50 if (!BrotliPullByte(br)) {
51 /* If we consumed all the input, we don't care about the alignment. */
52 return BROTLI_TRUE;
53 }
54 }
55 return BROTLI_TRUE;
56}
57
58BROTLI_BOOL BrotliSafeReadBits32Slow(BrotliBitReader* const br,
59 uint32_t n_bits, uint32_t* val) {
60 uint32_t low_val;
61 uint32_t high_val;
62 BrotliBitReaderState memento;
63 BROTLI_DCHECK(n_bits <= 32);
64 BROTLI_DCHECK(n_bits > 24);
65 BrotliBitReaderSaveState(br, &memento);
66 if (!BrotliSafeReadBits(br, 16, &low_val) ||
67 !BrotliSafeReadBits(br, n_bits - 16, &high_val)) {
68 BrotliBitReaderRestoreState(br, &memento);
69 return BROTLI_FALSE;
70 }
71 *val = low_val | (high_val << 16);
72 return BROTLI_TRUE;
73}
74
75#if defined(__cplusplus) || defined(c_plusplus)
76} /* extern "C" */
77#endif
78