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// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#include "draco/compression/bit_coders/adaptive_rans_bit_decoder.h"
#include "draco/compression/bit_coders/adaptive_rans_bit_coding_shared.h"
namespace draco {
AdaptiveRAnsBitDecoder::AdaptiveRAnsBitDecoder() : p0_f_(0.5) {}
AdaptiveRAnsBitDecoder::~AdaptiveRAnsBitDecoder() { Clear(); }
bool AdaptiveRAnsBitDecoder::StartDecoding(DecoderBuffer *source_buffer) {
Clear();
uint32_t size_in_bytes;
if (!source_buffer->Decode(&size_in_bytes)) {
return false;
}
if (size_in_bytes > source_buffer->remaining_size()) {
return false;
}
if (ans_read_init(&ans_decoder_,
reinterpret_cast<uint8_t *>(
const_cast<char *>(source_buffer->data_head())),
size_in_bytes) != 0) {
return false;
}
source_buffer->Advance(size_in_bytes);
return true;
}
bool AdaptiveRAnsBitDecoder::DecodeNextBit() {
const uint8_t p0 = clamp_probability(p0_f_);
const bool bit = static_cast<bool>(rabs_read(&ans_decoder_, p0));
p0_f_ = update_probability(p0_f_, bit);
return bit;
}
void AdaptiveRAnsBitDecoder::DecodeLeastSignificantBits32(int nbits,
uint32_t *value) {
DRACO_DCHECK_EQ(true, nbits <= 32);
DRACO_DCHECK_EQ(true, nbits > 0);
uint32_t result = 0;
while (nbits) {
result = (result << 1) + DecodeNextBit();
--nbits;
}
*value = result;
}
void AdaptiveRAnsBitDecoder::Clear() {
ans_read_end(&ans_decoder_);
p0_f_ = 0.5;
}
} // namespace draco
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