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      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 
     29 void BrotliInitBitReader(BrotliBitReader* const br) {
     30   br->val_ = 0;
     31   br->bit_pos_ = sizeof(br->val_) << 3;
     32 }
     33 
     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 
     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