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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/rans_bit_decoder.h"
#include "draco/compression/config/compression_shared.h"
#include "draco/core/bit_utils.h"
#include "draco/core/varint_decoding.h"
namespace draco {
RAnsBitDecoder::RAnsBitDecoder() : prob_zero_(0) {}
RAnsBitDecoder::~RAnsBitDecoder() { Clear(); }
bool RAnsBitDecoder::StartDecoding(DecoderBuffer *source_buffer) {
Clear();
if (!source_buffer->Decode(&prob_zero_))
return false;
uint32_t size_in_bytes;
#ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
if (source_buffer->bitstream_version() < DRACO_BITSTREAM_VERSION(2, 2)) {
if (!source_buffer->Decode(&size_in_bytes))
return false;
} else
#endif
{
if (!DecodeVarint(&size_in_bytes, source_buffer))
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 RAnsBitDecoder::DecodeNextBit() {
const uint8_t bit = rabs_read(&ans_decoder_, prob_zero_);
return bit > 0;
}
void RAnsBitDecoder::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 RAnsBitDecoder::Clear() { ans_read_end(&ans_decoder_); }
} // namespace draco
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