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https://git.mirrors.martin98.com/https://github.com/google/draco
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143 lines
4.0 KiB
C++
143 lines
4.0 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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// File provides direct encoding of bits with arthmetic encoder interface.
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#ifndef DRACO_CORE_DIRECT_BIT_CODING_H_
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#define DRACO_CORE_DIRECT_BIT_CODING_H_
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#include <vector>
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#include "core/decoder_buffer.h"
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#include "core/encoder_buffer.h"
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namespace draco {
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class DirectBitEncoder {
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public:
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DirectBitEncoder();
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~DirectBitEncoder();
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// Must be called before any Encode* function is called.
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void StartEncoding();
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// Encode one bit. If |bit| is true encode a 1, otherwise encode a 0.
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void EncodeBit(bool bit) {
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if (bit) {
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local_bits_ |= 1 << (31 - num_local_bits_);
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}
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num_local_bits_++;
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if (num_local_bits_ == 32) {
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bits_.push_back(local_bits_);
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num_local_bits_ = 0;
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local_bits_ = 0;
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}
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}
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// Encode |nibts| of |value|, starting from the least significant bit.
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// |nbits| must be > 0 and <= 32.
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void EncodeBits32(int nbits, 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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const int remaining = 32 - num_local_bits_;
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// Make sure there are no leading bits that should not be encoded and
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// start from here.
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value = value << (32 - nbits);
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if (nbits <= remaining) {
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value = value >> num_local_bits_;
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local_bits_ = local_bits_ | value;
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num_local_bits_ += nbits;
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if (num_local_bits_ == 32) {
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bits_.push_back(local_bits_);
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local_bits_ = 0;
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num_local_bits_ = 0;
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}
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} else {
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value = value >> (32 - nbits);
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num_local_bits_ = nbits - remaining;
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const uint32_t value_l = value >> num_local_bits_;
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local_bits_ = local_bits_ | value_l;
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bits_.push_back(local_bits_);
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local_bits_ = value << (32 - num_local_bits_);
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}
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}
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// Ends the bit encoding and stores the result into the target_buffer.
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void EndEncoding(EncoderBuffer *target_buffer);
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private:
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void Clear();
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std::vector<uint32_t> bits_;
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uint32_t local_bits_;
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uint32_t num_local_bits_;
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};
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class DirectBitDecoder {
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public:
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DirectBitDecoder();
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~DirectBitDecoder();
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// Sets |source_buffer| as the buffer to decode bits from.
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void StartDecoding(DecoderBuffer *source_buffer);
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// Decode one bit. Returns true if the bit is a 1, otherwsie false.
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bool DecodeNextBit() {
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const uint32_t selector = 1 << (31 - num_used_bits_);
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const bool bit = *pos_ & selector;
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++num_used_bits_;
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if (num_used_bits_ == 32) {
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++pos_;
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num_used_bits_ = 0;
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}
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return bit;
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}
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// Decode the next |nbits| and return the sequence in |value|. |nbits| must be
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// > 0 and <= 32.
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void DecodeBits32(int nbits, 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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const uint32_t remaining = 32 - num_used_bits_;
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if (nbits <= remaining) {
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*value = (*pos_ << num_used_bits_) >> (32 - nbits);
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num_used_bits_ += nbits;
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if (num_used_bits_ == 32) {
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++pos_;
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num_used_bits_ = 0;
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}
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} else {
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const uint32_t value_l = ((*pos_) << num_used_bits_);
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num_used_bits_ = nbits - remaining;
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++pos_;
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const uint32_t value_r = (*pos_) >> (32 - num_used_bits_);
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*value = (value_l >> (32 - num_used_bits_ - remaining)) | value_r;
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}
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}
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void EndDecoding() {}
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private:
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void Clear();
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std::vector<uint32_t> bits_;
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std::vector<uint32_t>::const_iterator pos_;
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uint32_t num_used_bits_;
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};
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} // namespace draco
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#endif // DRACO_CORE_DIRECT_BIT_CODING_H_
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