1 // Copyright 2018 Google LLC 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef ASTC_CODEC_BASE_BIT_STREAM_H_ 16 #define ASTC_CODEC_BASE_BIT_STREAM_H_ 17 18 #include <cassert> 19 #include <cstdint> 20 21 namespace astc_codec { 22 namespace base { 23 24 // Represents a stream of bits that can be read or written in arbitrary-sized 25 // chunks. 26 template<typename IntType = uint64_t> 27 class BitStream { 28 public: 29 // Creates an empty BitStream. 30 BitStream() = default; BitStream(IntType data,uint32_t data_size)31 BitStream(IntType data, uint32_t data_size) 32 : data_(data), data_size_(data_size) { 33 assert(data_size_ <= sizeof(data_) * 8); 34 } 35 36 // Return the number of bits in the stream. Bits()37 uint32_t Bits() const { return data_size_; } 38 39 // Put |size| bits into the stream. 40 // Fails if there is not enough space in the buffer to store the bits. 41 template<typename ResultType> PutBits(ResultType x,uint32_t size)42 void PutBits(ResultType x, uint32_t size) { 43 assert(data_size_ + size <= sizeof(data_) * 8); 44 45 data_ |= (IntType(x) & MaskFor(size)) << data_size_; 46 data_size_ += size; 47 } 48 49 // Get |count| bits from the stream. 50 // Returns true if |count| bits were successfully retrieved. 51 template<typename ResultType> GetBits(uint32_t count,ResultType * result)52 bool GetBits(uint32_t count, ResultType* result) { 53 if (count <= data_size_) { 54 *result = static_cast<ResultType>(data_ & MaskFor(count)); 55 data_ = data_ >> count; 56 data_size_ -= count; 57 return true; 58 } else { 59 *result = ResultType(); 60 return false; 61 } 62 } 63 64 private: MaskFor(uint32_t bits)65 IntType MaskFor(uint32_t bits) const { 66 return (bits == sizeof(IntType) * 8) ? ~IntType(0) 67 : (IntType(1) << bits) - 1; 68 } 69 70 IntType data_ = IntType(); 71 uint32_t data_size_ = 0; 72 }; 73 74 } // namespace base 75 } // namespace astc_codec 76 77 #endif // ASTC_CODEC_BASE_BIT_STREAM_H_ 78