src/utils/bit_writer.c

// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
//  Software License Agreement:  http://www.webmproject.org/license/software/
//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Bit writing and boolean coder
//
// Author: Skal (pascal.massimino@gmail.com)
//         Vikas Arora (vikaas.arora@gmail.com)

#include <assert.h>
#include <string.h>   // for memcpy()
#include <stdlib.h>
#include "./bit_writer.h"

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

//------------------------------------------------------------------------------
// VP8BitWriter

static int BitWriterResize(VP8BitWriter* const bw, size_t extra_size) {
  uint8_t* new_buf;
  size_t new_size;
  const uint64_t needed_size_64b = (uint64_t)bw->pos_ + extra_size;
  const size_t needed_size = (size_t)needed_size_64b;
  if (needed_size_64b != needed_size) {
    bw->error_ = 1;
    return 0;
  }
  if (needed_size <= bw->max_pos_) return 1;
  // If the following line wraps over 32bit, the test just after will catch it.
  new_size = 2 * bw->max_pos_;
  if (new_size < needed_size) new_size = needed_size;
  if (new_size < 1024) new_size = 1024;
  new_buf = (uint8_t*)malloc(new_size);
  if (new_buf == NULL) {
    bw->error_ = 1;
    return 0;
  }
  memcpy(new_buf, bw->buf_, bw->pos_);
  free(bw->buf_);
  bw->buf_ = new_buf;
  bw->max_pos_ = new_size;
  return 1;
}

static void kFlush(VP8BitWriter* const bw) {
  const int s = 8 + bw->nb_bits_;
  const int32_t bits = bw->value_ >> s;
  assert(bw->nb_bits_ >= 0);
  bw->value_ -= bits << s;
  bw->nb_bits_ -= 8;
  if ((bits & 0xff) != 0xff) {
    size_t pos = bw->pos_;
    if (!BitWriterResize(bw, bw->run_ + 1)) {
      return;
    }
    if (bits & 0x100) {  // overflow -> propagate carry over pending 0xff's
      if (pos > 0) bw->buf_[pos - 1]++;
    }
    if (bw->run_ > 0) {
      const int value = (bits & 0x100) ? 0x00 : 0xff;
      for (; bw->run_ > 0; --bw->run_) bw->buf_[pos++] = value;
    }
    bw->buf_[pos++] = bits;
    bw->pos_ = pos;
  } else {
    bw->run_++;   // delay writing of bytes 0xff, pending eventual carry.
  }
}

//------------------------------------------------------------------------------
// renormalization

static const uint8_t kNorm[128] = {  // renorm_sizes[i] = 8 - log2(i)
     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
static const uint8_t kNewRange[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
};

int VP8PutBit(VP8BitWriter* const bw, int bit, int prob) {
  const int split = (bw->range_ * prob) >> 8;
  if (bit) {
    bw->value_ += split + 1;
    bw->range_ -= split + 1;
  } else {
    bw->range_ = split;
  }
  if (bw->range_ < 127) {   // emit 'shift' bits out and renormalize
    const int shift = kNorm[bw->range_];
    bw->range_ = kNewRange[bw->range_];
    bw->value_ <<= shift;
    bw->nb_bits_ += shift;
    if (bw->nb_bits_ > 0) kFlush(bw);
  }
  return bit;
}

int VP8PutBitUniform(VP8BitWriter* const bw, int bit) {
  const int split = bw->range_ >> 1;
  if (bit) {
    bw->value_ += split + 1;
    bw->range_ -= split + 1;
  } else {
    bw->range_ = split;
  }
  if (bw->range_ < 127) {
    bw->range_ = kNewRange[bw->range_];
    bw->value_ <<= 1;
    bw->nb_bits_ += 1;
    if (bw->nb_bits_ > 0) kFlush(bw);
  }
  return bit;
}

void VP8PutValue(VP8BitWriter* const bw, int value, int nb_bits) {
  int mask;
  for (mask = 1 << (nb_bits - 1); mask; mask >>= 1)
    VP8PutBitUniform(bw, value & mask);
}

void VP8PutSignedValue(VP8BitWriter* const bw, int value, int nb_bits) {
  if (!VP8PutBitUniform(bw, value != 0))
    return;
  if (value < 0) {
    VP8PutValue(bw, ((-value) << 1) | 1, nb_bits + 1);
  } else {
    VP8PutValue(bw, value << 1, nb_bits + 1);
  }
}

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

int VP8BitWriterInit(VP8BitWriter* const bw, size_t expected_size) {
  bw->range_   = 255 - 1;
  bw->value_   = 0;
  bw->run_     = 0;
  bw->nb_bits_ = -8;
  bw->pos_     = 0;
  bw->max_pos_ = 0;
  bw->error_   = 0;
  bw->buf_     = NULL;
  return (expected_size > 0) ? BitWriterResize(bw, expected_size) : 1;
}

uint8_t* VP8BitWriterFinish(VP8BitWriter* const bw) {
  VP8PutValue(bw, 0, 9 - bw->nb_bits_);
  bw->nb_bits_ = 0;   // pad with zeroes
  kFlush(bw);
  return bw->buf_;
}

int VP8BitWriterAppend(VP8BitWriter* const bw,
                       const uint8_t* data, size_t size) {
  assert(data);
  if (bw->nb_bits_ != -8) return 0;   // kFlush() must have been called
  if (!BitWriterResize(bw, size)) return 0;
  memcpy(bw->buf_ + bw->pos_, data, size);
  bw->pos_ += size;
  return 1;
}

void VP8BitWriterWipeOut(VP8BitWriter* const bw) {
  if (bw) {
    free(bw->buf_);
    memset(bw, 0, sizeof(*bw));
  }
}

//------------------------------------------------------------------------------
// VP8LBitWriter

// Returns 1 on success.
static int VP8LBitWriterResize(VP8LBitWriter* const bw, size_t extra_size) {
  uint8_t* allocated_buf;
  size_t allocated_size;
  const size_t current_size = VP8LBitWriterNumBytes(bw);
  const uint64_t size_required_64b = (uint64_t)current_size + extra_size;
  const size_t size_required = (size_t)size_required_64b;
  if (size_required != size_required_64b) {
    bw->error_ = 1;
    return 0;
  }
  if (bw->max_bytes_ > 0 && size_required <= bw->max_bytes_) return 1;
  allocated_size = (3 * bw->max_bytes_) >> 1;
  if (allocated_size < size_required) allocated_size = size_required;
  // make allocated size multiple of 1k
  allocated_size = (((allocated_size >> 10) + 1) << 10);
  allocated_buf = (uint8_t*)malloc(allocated_size);
  if (allocated_buf == NULL) {
    bw->error_ = 1;
    return 0;
  }
  memcpy(allocated_buf, bw->buf_, current_size);
  free(bw->buf_);
  bw->buf_ = allocated_buf;
  bw->max_bytes_ = allocated_size;
  memset(allocated_buf + current_size, 0, allocated_size - current_size);
  return 1;
}

int VP8LBitWriterInit(VP8LBitWriter* const bw, size_t expected_size) {
  memset(bw, 0, sizeof(*bw));
  return VP8LBitWriterResize(bw, expected_size);
}

void VP8LBitWriterDestroy(VP8LBitWriter* const bw) {
  if (bw != NULL) {
    free(bw->buf_);
    memset(bw, 0, sizeof(*bw));
  }
}

void VP8LWriteBits(VP8LBitWriter* const bw, int n_bits, uint32_t bits) {
  if (n_bits < 1) return;
#if !defined(__BIG_ENDIAN__)
  // Technically, this branch of the code can write up to 25 bits at a time,
  // but in prefix encoding, the maximum number of bits written is 18 at a time.
  {
    uint8_t* const p = &bw->buf_[bw->bit_pos_ >> 3];
    uint32_t v = *(const uint32_t*)p;
    v |= bits << (bw->bit_pos_ & 7);
    *(uint32_t*)p = v;
    bw->bit_pos_ += n_bits;
  }
#else  // BIG_ENDIAN
  {
    uint8_t* p = &bw->buf_[bw->bit_pos_ >> 3];
    const int bits_reserved_in_first_byte = bw->bit_pos_ & 7;
    const int bits_left_to_write = n_bits - 8 + bits_reserved_in_first_byte;
    // implicit & 0xff is assumed for uint8_t arithmetics
    *p++ |= bits << bits_reserved_in_first_byte;
    bits >>= 8 - bits_reserved_in_first_byte;
    if (bits_left_to_write >= 1) {
      *p++ = bits;
      bits >>= 8;
      if (bits_left_to_write >= 9) {
        *p++ = bits;
        bits >>= 8;
      }
    }
    assert(n_bits <= 25);
    *p = bits;
    bw->bit_pos_ += n_bits;
  }
#endif
  if ((bw->bit_pos_ >> 3) > (bw->max_bytes_ - 8)) {
    const uint64_t extra_size = 32768ULL + bw->max_bytes_;
    if (extra_size != (size_t)extra_size ||
        !VP8LBitWriterResize(bw, (size_t)extra_size)) {
      bw->bit_pos_ = 0;
      bw->error_ = 1;
    }
  }
}

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

#if defined(__cplusplus) || defined(c_plusplus)
}    // extern "C"
#endif