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