draco/core/direct_bit_coding.h
2016-12-12 16:39:06 -08:00

143 lines
4.0 KiB
C++

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