1 // Copyright 2016 The Draco Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 #include "draco/compression/bit_coders/adaptive_rans_bit_encoder.h"
16
17 #include "draco/compression/bit_coders/adaptive_rans_bit_coding_shared.h"
18
19 namespace draco {
20
AdaptiveRAnsBitEncoder()21 AdaptiveRAnsBitEncoder::AdaptiveRAnsBitEncoder() {}
22
~AdaptiveRAnsBitEncoder()23 AdaptiveRAnsBitEncoder::~AdaptiveRAnsBitEncoder() { Clear(); }
24
StartEncoding()25 void AdaptiveRAnsBitEncoder::StartEncoding() { Clear(); }
26
EndEncoding(EncoderBuffer * target_buffer)27 void AdaptiveRAnsBitEncoder::EndEncoding(EncoderBuffer *target_buffer) {
28 // Buffer for ans to write.
29 std::vector<uint8_t> buffer(bits_.size() + 16);
30 AnsCoder ans_coder;
31 ans_write_init(&ans_coder, buffer.data());
32
33 // Unfortunately we have to encode the bits in reversed order, while the
34 // probabilities that should be given are those of the forward sequence.
35 double p0_f = 0.5;
36 std::vector<uint8_t> p0s;
37 p0s.reserve(bits_.size());
38 for (bool b : bits_) {
39 p0s.push_back(clamp_probability(p0_f));
40 p0_f = update_probability(p0_f, b);
41 }
42 auto bit = bits_.rbegin();
43 auto pit = p0s.rbegin();
44 while (bit != bits_.rend()) {
45 rabs_write(&ans_coder, *bit, *pit);
46 ++bit;
47 ++pit;
48 }
49
50 const uint32_t size_in_bytes = ans_write_end(&ans_coder);
51 target_buffer->Encode(size_in_bytes);
52 target_buffer->Encode(buffer.data(), size_in_bytes);
53
54 Clear();
55 }
56
Clear()57 void AdaptiveRAnsBitEncoder::Clear() { bits_.clear(); }
58
59 } // namespace draco
60