bit_reader_utils.c 6.69 KB
Newer Older
wester committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222
// Copyright 2010 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Boolean decoder non-inlined methods
//
// Author: Skal (pascal.massimino@gmail.com)

#ifdef HAVE_CONFIG_H
#include "../webp/config.h"
#endif

#include "./bit_reader_inl_utils.h"
#include "../utils/utils.h"

//------------------------------------------------------------------------------
// VP8BitReader

void VP8BitReaderSetBuffer(VP8BitReader* const br,
                           const uint8_t* const start,
                           size_t size) {
  br->buf_     = start;
  br->buf_end_ = start + size;
  br->buf_max_ =
      (size >= sizeof(lbit_t)) ? start + size - sizeof(lbit_t) + 1
                               : start;
}

void VP8InitBitReader(VP8BitReader* const br,
                      const uint8_t* const start, size_t size) {
  assert(br != NULL);
  assert(start != NULL);
  assert(size < (1u << 31));   // limit ensured by format and upstream checks
  br->range_   = 255 - 1;
  br->value_   = 0;
  br->bits_    = -8;   // to load the very first 8bits
  br->eof_     = 0;
  VP8BitReaderSetBuffer(br, start, size);
  VP8LoadNewBytes(br);
}

void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset) {
  if (br->buf_ != NULL) {
    br->buf_ += offset;
    br->buf_end_ += offset;
    br->buf_max_ += offset;
  }
}

const uint8_t kVP8Log2Range[128] = {
     7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
  3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  0
};

// range = ((range - 1) << kVP8Log2Range[range]) + 1
const uint8_t kVP8NewRange[128] = {
  127, 127, 191, 127, 159, 191, 223, 127,
  143, 159, 175, 191, 207, 223, 239, 127,
  135, 143, 151, 159, 167, 175, 183, 191,
  199, 207, 215, 223, 231, 239, 247, 127,
  131, 135, 139, 143, 147, 151, 155, 159,
  163, 167, 171, 175, 179, 183, 187, 191,
  195, 199, 203, 207, 211, 215, 219, 223,
  227, 231, 235, 239, 243, 247, 251, 127,
  129, 131, 133, 135, 137, 139, 141, 143,
  145, 147, 149, 151, 153, 155, 157, 159,
  161, 163, 165, 167, 169, 171, 173, 175,
  177, 179, 181, 183, 185, 187, 189, 191,
  193, 195, 197, 199, 201, 203, 205, 207,
  209, 211, 213, 215, 217, 219, 221, 223,
  225, 227, 229, 231, 233, 235, 237, 239,
  241, 243, 245, 247, 249, 251, 253, 127
};

void VP8LoadFinalBytes(VP8BitReader* const br) {
  assert(br != NULL && br->buf_ != NULL);
  // Only read 8bits at a time
  if (br->buf_ < br->buf_end_) {
    br->bits_ += 8;
    br->value_ = (bit_t)(*br->buf_++) | (br->value_ << 8);
  } else if (!br->eof_) {
    br->value_ <<= 8;
    br->bits_ += 8;
    br->eof_ = 1;
  } else {
    br->bits_ = 0;  // This is to avoid undefined behaviour with shifts.
  }
}

//------------------------------------------------------------------------------
// Higher-level calls

uint32_t VP8GetValue(VP8BitReader* const br, int bits) {
  uint32_t v = 0;
  while (bits-- > 0) {
    v |= VP8GetBit(br, 0x80) << bits;
  }
  return v;
}

int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
  const int value = VP8GetValue(br, bits);
  return VP8Get(br) ? -value : value;
}

//------------------------------------------------------------------------------
// VP8LBitReader

#define VP8L_LOG8_WBITS 4  // Number of bytes needed to store VP8L_WBITS bits.

#if defined(__arm__) || defined(_M_ARM) || defined(__aarch64__) || \
    defined(__i386__) || defined(_M_IX86) || \
    defined(__x86_64__) || defined(_M_X64)
#define VP8L_USE_FAST_LOAD
#endif

static const uint32_t kBitMask[VP8L_MAX_NUM_BIT_READ + 1] = {
  0,
  0x000001, 0x000003, 0x000007, 0x00000f,
  0x00001f, 0x00003f, 0x00007f, 0x0000ff,
  0x0001ff, 0x0003ff, 0x0007ff, 0x000fff,
  0x001fff, 0x003fff, 0x007fff, 0x00ffff,
  0x01ffff, 0x03ffff, 0x07ffff, 0x0fffff,
  0x1fffff, 0x3fffff, 0x7fffff, 0xffffff
};

void VP8LInitBitReader(VP8LBitReader* const br, const uint8_t* const start,
                       size_t length) {
  size_t i;
  vp8l_val_t value = 0;
  assert(br != NULL);
  assert(start != NULL);
  assert(length < 0xfffffff8u);   // can't happen with a RIFF chunk.

  br->len_ = length;
  br->val_ = 0;
  br->bit_pos_ = 0;
  br->eos_ = 0;

  if (length > sizeof(br->val_)) {
    length = sizeof(br->val_);
  }
  for (i = 0; i < length; ++i) {
    value |= (vp8l_val_t)start[i] << (8 * i);
  }
  br->val_ = value;
  br->pos_ = length;
  br->buf_ = start;
}

void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
                            const uint8_t* const buf, size_t len) {
  assert(br != NULL);
  assert(buf != NULL);
  assert(len < 0xfffffff8u);   // can't happen with a RIFF chunk.
  br->buf_ = buf;
  br->len_ = len;
  // pos_ > len_ should be considered a param error.
  br->eos_ = (br->pos_ > br->len_) || VP8LIsEndOfStream(br);
}

static void VP8LSetEndOfStream(VP8LBitReader* const br) {
  br->eos_ = 1;
  br->bit_pos_ = 0;  // To avoid undefined behaviour with shifts.
}

// If not at EOS, reload up to VP8L_LBITS byte-by-byte
static void ShiftBytes(VP8LBitReader* const br) {
  while (br->bit_pos_ >= 8 && br->pos_ < br->len_) {
    br->val_ >>= 8;
    br->val_ |= ((vp8l_val_t)br->buf_[br->pos_]) << (VP8L_LBITS - 8);
    ++br->pos_;
    br->bit_pos_ -= 8;
  }
  if (VP8LIsEndOfStream(br)) {
    VP8LSetEndOfStream(br);
  }
}

void VP8LDoFillBitWindow(VP8LBitReader* const br) {
  assert(br->bit_pos_ >= VP8L_WBITS);
#if defined(VP8L_USE_FAST_LOAD)
  if (br->pos_ + sizeof(br->val_) < br->len_) {
    br->val_ >>= VP8L_WBITS;
    br->bit_pos_ -= VP8L_WBITS;
    br->val_ |= (vp8l_val_t)HToLE32(WebPMemToUint32(br->buf_ + br->pos_)) <<
                (VP8L_LBITS - VP8L_WBITS);
    br->pos_ += VP8L_LOG8_WBITS;
    return;
  }
#endif
  ShiftBytes(br);       // Slow path.
}

uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits) {
  assert(n_bits >= 0);
  // Flag an error if end_of_stream or n_bits is more than allowed limit.
  if (!br->eos_ && n_bits <= VP8L_MAX_NUM_BIT_READ) {
    const uint32_t val = VP8LPrefetchBits(br) & kBitMask[n_bits];
    const int new_bits = br->bit_pos_ + n_bits;
    br->bit_pos_ = new_bits;
    ShiftBytes(br);
    return val;
  } else {
    VP8LSetEndOfStream(br);
    return 0;
  }
}

//------------------------------------------------------------------------------