1 // Copyright 2016 The Draco Authors. 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 // http://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 // File provides direct encoding of bits with arithmetic encoder interface. 16 #ifndef DRACO_COMPRESSION_BIT_CODERS_DIRECT_BIT_DECODER_H_ 17 #define DRACO_COMPRESSION_BIT_CODERS_DIRECT_BIT_DECODER_H_ 18 19 #include <vector> 20 21 #include "draco/core/decoder_buffer.h" 22 23 namespace draco { 24 25 class DirectBitDecoder { 26 public: 27 DirectBitDecoder(); 28 ~DirectBitDecoder(); 29 30 // Sets |source_buffer| as the buffer to decode bits from. 31 bool StartDecoding(DecoderBuffer *source_buffer); 32 33 // Decode one bit. Returns true if the bit is a 1, otherwise false. DecodeNextBit()34 bool DecodeNextBit() { 35 const uint32_t selector = 1 << (31 - num_used_bits_); 36 if (pos_ == bits_.end()) { 37 return false; 38 } 39 const bool bit = *pos_ & selector; 40 ++num_used_bits_; 41 if (num_used_bits_ == 32) { 42 ++pos_; 43 num_used_bits_ = 0; 44 } 45 return bit; 46 } 47 48 // Decode the next |nbits| and return the sequence in |value|. |nbits| must be 49 // > 0 and <= 32. DecodeLeastSignificantBits32(int nbits,uint32_t * value)50 void DecodeLeastSignificantBits32(int nbits, uint32_t *value) { 51 DRACO_DCHECK_EQ(true, nbits <= 32); 52 DRACO_DCHECK_EQ(true, nbits > 0); 53 const int remaining = 32 - num_used_bits_; 54 if (nbits <= remaining) { 55 if (pos_ == bits_.end()) { 56 *value = 0; 57 return; 58 } 59 *value = (*pos_ << num_used_bits_) >> (32 - nbits); 60 num_used_bits_ += nbits; 61 if (num_used_bits_ == 32) { 62 ++pos_; 63 num_used_bits_ = 0; 64 } 65 } else { 66 if (pos_ + 1 == bits_.end()) { 67 *value = 0; 68 return; 69 } 70 const uint32_t value_l = ((*pos_) << num_used_bits_); 71 num_used_bits_ = nbits - remaining; 72 ++pos_; 73 const uint32_t value_r = (*pos_) >> (32 - num_used_bits_); 74 *value = (value_l >> (32 - num_used_bits_ - remaining)) | value_r; 75 } 76 } 77 EndDecoding()78 void EndDecoding() {} 79 80 private: 81 void Clear(); 82 83 std::vector<uint32_t> bits_; 84 std::vector<uint32_t>::const_iterator pos_; 85 uint32_t num_used_bits_; 86 }; 87 88 } // namespace draco 89 90 #endif // DRACO_COMPRESSION_BIT_CODERS_DIRECT_BIT_DECODER_H_ 91