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// Copyright 2018 Google LLC
//
// 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
//
// https://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.
#ifndef ASTC_CODEC_BASE_BIT_STREAM_H_
#define ASTC_CODEC_BASE_BIT_STREAM_H_
#include <cassert>
#include <cstdint>
namespace astc_codec {
namespace base {
// Represents a stream of bits that can be read or written in arbitrary-sized
// chunks.
template<typename IntType = uint64_t>
class BitStream {
public:
// Creates an empty BitStream.
BitStream() = default;
BitStream(IntType data, uint32_t data_size)
: data_(data), data_size_(data_size) {
assert(data_size_ <= sizeof(data_) * 8);
}
// Return the number of bits in the stream.
uint32_t Bits() const { return data_size_; }
// Put |size| bits into the stream.
// Fails if there is not enough space in the buffer to store the bits.
template<typename ResultType>
void PutBits(ResultType x, uint32_t size) {
assert(data_size_ + size <= sizeof(data_) * 8);
data_ |= (IntType(x) & MaskFor(size)) << data_size_;
data_size_ += size;
}
// Get |count| bits from the stream.
// Returns true if |count| bits were successfully retrieved.
template<typename ResultType>
bool GetBits(uint32_t count, ResultType* result) {
if (count <= data_size_) {
*result = static_cast<ResultType>(data_ & MaskFor(count));
data_ = data_ >> count;
data_size_ -= count;
return true;
} else {
*result = ResultType();
return false;
}
}
private:
IntType MaskFor(uint32_t bits) const {
return (bits == sizeof(IntType) * 8) ? ~IntType(0)
: (IntType(1) << bits) - 1;
}
IntType data_ = IntType();
uint32_t data_size_ = 0;
};
} // namespace base
} // namespace astc_codec
#endif // ASTC_CODEC_BASE_BIT_STREAM_H_
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