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)
15extern "C" {
16#endif
17
18const 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
29void BrotliInitBitReader(BrotliBitReader* const br) {
30  br->val_ = 0;
31  br->bit_pos_ = sizeof(br->val_) << 3;
32}
33
34BROTLI_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
57BROTLI_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