diff options
Diffstat (limited to 'src/enc/bit_writer.c')
-rw-r--r-- | src/enc/bit_writer.c | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/src/enc/bit_writer.c b/src/enc/bit_writer.c new file mode 100644 index 00000000..3656a7e2 --- /dev/null +++ b/src/enc/bit_writer.c @@ -0,0 +1,175 @@ +// Copyright 2011 Google Inc. +// +// 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) + +#include <assert.h> +#include <stdlib.h> +#include "vp8enci.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 size_t needed_size = bw->pos_ + extra_size; + if (needed_size <= bw->max_pos_) return 1; + 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; + } + if (bw->pos_ > 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 (pos + bw->run_ >= bw->max_pos_) { // reallocate + 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 +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_; +} + +//----------------------------------------------------------------------------- + +#if defined(__cplusplus) || defined(c_plusplus) +} // extern "C" +#endif |