libwebp/enc/bit_writer.c

23 static int BitWriterResize(VP8BitWriter* const bw, size_t extra_size) {
26   const size_t needed_size = bw->pos_ + extra_size;
27   if (needed_size <= bw->max_pos_) return 1;
28   new_size = 2 * bw->max_pos_;
34     bw->error_ = 1;
37   if (bw->pos_ > 0) memcpy(new_buf, bw->buf_, bw->pos_);
38   free(bw->buf_);
39   bw->buf_ = new_buf;
40   bw->max_pos_ = new_size;
44 static void kFlush(VP8BitWriter* const bw) {
45   const int s = 8 + bw->nb_bits_;
46   const int32_t bits = bw->value_ >> s;
47   assert(bw->nb_bits_ >= 0);
48   bw->value_ -= bits << s;
49   bw->nb_bits_ -= 8;
51     size_t pos = bw->pos_;
52     if (pos + bw->run_ >= bw->max_pos_) {  // reallocate
53       if (!BitWriterResize(bw,  bw->run_ + 1)) {
58       if (pos > 0) bw->buf_[pos - 1]++;
60     if (bw->run_ > 0) {
62       for (; bw->run_ > 0; --bw->run_) bw->buf_[pos++] = value;
64     bw->buf_[pos++] = bits;
65     bw->pos_ = pos;
67     bw->run_++;   // delay writing of bytes 0xff, pending eventual carry.
99 int VP8PutBit(VP8BitWriter* const bw, int bit, int prob) {
100   const int split = (bw->range_ * prob) >> 8;
102     bw->value_ += split + 1;
103     bw->range_ -= split + 1;
105     bw->range_ = split;
107   if (bw->range_ < 127) {   // emit 'shift' bits out and renormalize
108     const int shift = kNorm[bw->range_];
109     bw->range_ = kNewRange[bw->range_];
110     bw->value_ <<= shift;
111     bw->nb_bits_ += shift;
112     if (bw->nb_bits_ > 0) kFlush(bw);
117 int VP8PutBitUniform(VP8BitWriter* const bw, int bit) {
118   const int split = bw->range_ >> 1;
120     bw->value_ += split + 1;
121     bw->range_ -= split + 1;
123     bw->range_ = split;
125   if (bw->range_ < 127) {
126     bw->range_ = kNewRange[bw->range_];
127     bw->value_ <<= 1;
128     bw->nb_bits_ += 1;
129     if (bw->nb_bits_ > 0) kFlush(bw);
134 void VP8PutValue(VP8BitWriter* const bw, int value, int nb_bits) {
137     VP8PutBitUniform(bw, value & mask);
140 void VP8PutSignedValue(VP8BitWriter* const bw, int value, int nb_bits) {
141   if (!VP8PutBitUniform(bw, value != 0))
144     VP8PutValue(bw, ((-value) << 1) | 1, nb_bits + 1);
146     VP8PutValue(bw, value << 1, nb_bits + 1);
152 int VP8BitWriterInit(VP8BitWriter* const bw, size_t expected_size) {
153   bw->range_   = 255 - 1;
154   bw->value_   = 0;
155   bw->run_     = 0;
156   bw->nb_bits_ = -8;
157   bw->pos_     = 0;
158   bw->max_pos_ = 0;
159   bw->error_   = 0;
160   bw->buf_     = NULL;
161   return (expected_size > 0) ? BitWriterResize(bw, expected_size) : 1;
164 uint8_t* VP8BitWriterFinish(VP8BitWriter* const bw) {
165   VP8PutValue(bw, 0, 8 - bw->nb_bits_);
166   bw->nb_bits_ = 0;   // pad with zeroes
167   kFlush(bw);
168   return bw->buf_;