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GeezerVison is showing github.com — AliceO2/Algorithm/include/Algorithm/BitstreamReader.h at dev · MFTDecoding/AliceO2 Expand file tree/ Copy pathBitstreamReader.hMore file actions 290 lines (263 loc) · 7.93 KB / Copy pathBitstreamReader.hFile metadata and controls290 lines (263 loc) · 7.93 KB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 // Copyright 2019-2020 CERN and copyright holders of ALICE O2. // See https://alice-o2.web.cern.ch/copyright for details of the copyright holders. // All rights not expressly granted are reserved. // // This software is distributed under the terms of the GNU General Public // License v3 (GPL Version 3), copied verbatim in the file "COPYING". // // In applying this license CERN does not waive the privileges and immunities // granted to it by virtue of its status as an Intergovernmental Organization // or submit itself to any jurisdiction. #ifndef BITSTREAMREADER_H #define BITSTREAMREADER_H /// @file BitstreamReader.h /// @author Matthias Richter /// @since 2019-06-05 /// @brief Utility class to provide bitstream access to an underlying resource #include <type_traits> #include <bitset> namespace o2 { namespace algorithm { /// @class BitStreamReader /// @brief Utility class to provide bitstream access to an underlying resource /// /// Allows to access bits of variable length, supports integral types and also /// bitsets as target type. At the moment, the access is in direction MSB -> LSB. /// /// BitstreamReader<uint8_t> reader(start, end); /// while (reader.good() && not reader.eof()) { /// // get an 8 bit value from the stream, moves the position /// uint8_t ivalue; /// reader.get(ivalue); /// /// // get a 13 bit bitset without moving the position /// std::bitset<13> value; /// reader.peek(value, value.size()); /// // e.g. use 7 bits of the data /// value >>= value.size() - 7; /// // move position by the specific number of bits /// reader.seek(7); /// } template <typename BufferType> class BitstreamReader { public: using self_type = BitstreamReader<BufferType>; // for the moment we simply use pointers, but with some traits this can be extended to // containers using value_type = BufferType; using iterator = const value_type*; static constexpr size_t value_size = sizeof(value_type) * 8; BitstreamReader() = delete; BitstreamReader(iterator start, iterator end) : mStart(start), mEnd(end), mCurrent(mStart), mBitPosition(value_size) { } ~BitstreamReader() = default; /// Check reader's state /// @return true if not in error state bool good() const { return mBitPosition > 0; } /// Indicates end of data /// @return true if end of resource is reached bool eof() const { return mCurrent == mEnd && mBitPosition > 0; } /// Reset the reader, start over at beginning void reset() { mCurrent = mStart; mBitPosition = value_size; } /// Get the next N bits without moving the read position /// if bitlength is smaller than the size of data type, result is aligned to LSB /// TODO: this also works nicely for bitsets, but then the bitlength has to be specified /// as template parameter, want to do a specific overload, but needs more work to catch /// all cases. /// @param v target variable passed by reference /// @return number of poked bits template <typename T, size_t N = sizeof(T) * 8> size_t peek(T& v) { static_assert(N <= sizeof(T) * 8); return peek<T, false>(v, N); } /// Get the next n bits without moving the read position /// if bitlength is smaller than the size of data type, result is aligned to LSB /// @param v target variable passed by reference /// @param bitlength number of bits to read /// @return number of poked bits template <typename T> size_t peek(T& v, size_t bitlength) { return peek<T, true>(v, bitlength); } /// Move read position /// @param bitlength move count in number of bits void seek(size_t bitlength) { while (good() && bitlength > 0 && mCurrent != mEnd) { if (bitlength >= mBitPosition) { bitlength -= mBitPosition; mBitPosition = 0; } else { mBitPosition -= bitlength; bitlength = 0; } if (mBitPosition == 0) { mCurrent++; mBitPosition = value_size; } } if (bitlength > 0) { mBitPosition = 0; } } /// Get the next n bits and move the read position template <typename T, size_t N = sizeof(T) * 8> T get() { T result; peek<T, N>(result); seek(N); return result; } /// Get the next n and move the read position template <typename T> T get(size_t bitlength = sizeof(T) * 8) { T result; peek<T>(result, bitlength); seek(bitlength); return result; } /// @class Bits /// @brief Helper class to get value of specified type which holds the number used bits /// /// The class holds both the extracted value access via peek method and the number of used /// bits. The reader will be incremented when the object is destroyed. /// The number of bits can be adjusted by using markUsed method template <typename FieldType, size_t N = sizeof(FieldType) * 8, typename ParentType = self_type> class Bits { public: using field_type = FieldType; static_assert(N <= sizeof(FieldType) * 8); Bits() : mParent(nullptr), mData(0), mLength(0) { } Bits(ParentType* parent, FieldType&& data) : mParent(parent), mData(std::move(data)), mLength(N) { } Bits(Bits&& other) : mParent(other.mParent), mData(std::move(other.mData)), mLength(other.mLength) { other.mParent = nullptr; other.mLength = 0; } ~Bits() { if (mParent) { mParent->seek(mLength); } } auto& operator=(Bits<FieldType, N, ParentType>&& other) { mParent = other.mParent; mData = std::move(other.mData); mLength = other.mLength; other.mParent = nullptr; other.mLength = 0; return *this; } FieldType& operator*() { return mData; } void markUsed(size_t length) { mLength = length; } private: ParentType* mParent; FieldType mData; size_t mLength; }; /// Read an integral value from the stream template <typename T, std::enable_if_t<std::is_integral<T>::value, int> = 0> self_type& operator>>(T& target) { target = get<T>(); return *this; } /// Read a bitstream value from the stream template <size_t N> self_type& operator>>(std::bitset<N>& target) { target = get<std::bitset<N>, N>(); return *this; } /// Read a Bits object from the stream template <typename T> self_type& operator>>(Bits<T>& target) { T bitfield; peek<T>(bitfield); target = std::move(Bits<T>(this, std::move(bitfield))); return *this; } private: /// The internal peek method template <typename T, bool RuntimeCheck> size_t peek(T& result, size_t bitlength) { if constexpr (RuntimeCheck) { // the runtime check is disabled if bitlength is derived at compile time if (bitlength > sizeof(T) * 8) { throw std::length_error(std::string("requested bit length ") + std::to_string(bitlength) + " does not fit size of result data type " + std::to_string(sizeof(T) * 8)); } } result = 0; size_t bitsToWrite = bitlength; auto current = mCurrent; auto bitsAvailable = mBitPosition; while (bitsToWrite > 0 && current != mEnd) { // extract available bits value_type mask = ~value_type(0) >> (value_size - bitsAvailable); if (bitsToWrite >= bitsAvailable) { T value = (*current & mask) << (bitsToWrite - bitsAvailable); result |= value; bitsToWrite -= bitsAvailable; bitsAvailable = 0; } else { value_type value = (*current & mask) >> (bitsAvailable - bitsToWrite); result |= value; bitsAvailable -= bitsToWrite; bitsToWrite = 0; } if (bitsAvailable == 0) { current++; bitsAvailable = value_size; } } return bitlength - bitsToWrite; } /// start of resource iterator mStart; /// end of resource iterator mEnd; /// current position in resource iterator mCurrent; /// bit position in current element size_t mBitPosition; }; } // namespace algorithm } // namespace o2 #endif |
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