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https://git.mirrors.martin98.com/https://github.com/google/draco
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3682ca2801
1. Add 'use strict'to example Javascript. 2. Small fixes to README.md. 3. Fix Draco compiler flag tests. 4. Fixed issue when number of quantized bits was to large. 5. Changed StartDecoding to return a value. 6. Check that num of attributes are not less than 0. 7. Check that the number of attributes is a valid value.
122 lines
3.5 KiB
C++
122 lines
3.5 KiB
C++
// Copyright 2016 The Draco Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#include "core/adaptive_rans_coding.h"
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#include <iostream>
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namespace draco {
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uint8_t clamp_probability(double p) {
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DCHECK_LE(p, 1.0);
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DCHECK_LE(0.0, p);
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uint32_t p_int = static_cast<uint32_t>((p * 256) + 0.5);
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p_int -= (p_int == 256);
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p_int += (p_int == 0);
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return static_cast<uint8_t>(p_int);
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}
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double update_probability(double old_p, bool bit) {
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static constexpr double w = 128.0;
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static constexpr double w0 = (w - 1.0) / w;
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static constexpr double w1 = 1.0 / w;
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return old_p * w0 + (!bit) * w1;
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}
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AdaptiveRAnsBitEncoder::AdaptiveRAnsBitEncoder() {}
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AdaptiveRAnsBitEncoder::~AdaptiveRAnsBitEncoder() { Clear(); }
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void AdaptiveRAnsBitEncoder::StartEncoding() { Clear(); }
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void AdaptiveRAnsBitEncoder::EndEncoding(EncoderBuffer *target_buffer) {
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// Buffer for ans to write.
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std::vector<uint8_t> buffer(bits_.size() + 16);
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AnsCoder ans_coder;
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ans_write_init(&ans_coder, buffer.data());
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// Unfortunaetly we have to encode the bits in reversed order, while the
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// probabilities that should be given are those of the forward sequence.
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double p0_f = 0.5;
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std::vector<uint8_t> p0s;
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p0s.reserve(bits_.size());
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for (bool b : bits_) {
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p0s.push_back(clamp_probability(p0_f));
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p0_f = update_probability(p0_f, b);
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}
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auto bit = bits_.rbegin();
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auto pit = p0s.rbegin();
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while (bit != bits_.rend()) {
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rabs_write(&ans_coder, *bit, *pit);
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++bit;
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++pit;
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}
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const uint32_t size_in_bytes = ans_write_end(&ans_coder);
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target_buffer->Encode(size_in_bytes);
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target_buffer->Encode(buffer.data(), size_in_bytes);
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Clear();
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}
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void AdaptiveRAnsBitEncoder::Clear() { bits_.clear(); }
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AdaptiveRAnsBitDecoder::AdaptiveRAnsBitDecoder() : p0_f_(0.5) {}
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AdaptiveRAnsBitDecoder::~AdaptiveRAnsBitDecoder() { Clear(); }
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bool AdaptiveRAnsBitDecoder::StartDecoding(DecoderBuffer *source_buffer) {
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Clear();
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uint32_t size_in_bytes;
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if (!source_buffer->Decode(&size_in_bytes))
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return false;
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if (size_in_bytes > source_buffer->remaining_size())
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return false;
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if (ans_read_init(&ans_decoder_,
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reinterpret_cast<uint8_t *>(
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const_cast<char *>(source_buffer->data_head())),
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size_in_bytes) != 0)
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return false;
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source_buffer->Advance(size_in_bytes);
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return true;
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}
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bool AdaptiveRAnsBitDecoder::DecodeNextBit() {
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const uint8_t p0 = clamp_probability(p0_f_);
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const bool bit = static_cast<bool>(rabs_read(&ans_decoder_, p0));
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p0_f_ = update_probability(p0_f_, bit);
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return bit;
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}
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void AdaptiveRAnsBitDecoder::DecodeLeastSignificantBits32(int nbits,
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uint32_t *value) {
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DCHECK_EQ(true, nbits <= 32);
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DCHECK_EQ(true, nbits > 0);
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uint32_t result = 0;
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while (nbits) {
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result = (result << 1) + DecodeNextBit();
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--nbits;
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}
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*value = result;
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}
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void AdaptiveRAnsBitDecoder::Clear() {
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ans_read_end(&ans_decoder_);
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p0_f_ = 0.5;
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}
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} // namespace draco
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