golombrice.h raw

   1  // Copyright (c) 2018-present The Bitcoin Core developers
   2  // Distributed under the MIT software license, see the accompanying
   3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4  
   5  #ifndef BITCOIN_UTIL_GOLOMBRICE_H
   6  #define BITCOIN_UTIL_GOLOMBRICE_H
   7  
   8  #include <util/fastrange.h>
   9  
  10  #include <streams.h>
  11  
  12  #include <cstdint>
  13  
  14  template <typename OStream>
  15  void GolombRiceEncode(BitStreamWriter<OStream>& bitwriter, uint8_t P, uint64_t x)
  16  {
  17      // Write quotient as unary-encoded: q 1's followed by one 0.
  18      uint64_t q = x >> P;
  19      while (q > 0) {
  20          int nbits = q <= 64 ? static_cast<int>(q) : 64;
  21          bitwriter.Write(~0ULL, nbits);
  22          q -= nbits;
  23      }
  24      bitwriter.Write(0, 1);
  25  
  26      // Write the remainder in P bits. Since the remainder is just the bottom
  27      // P bits of x, there is no need to mask first.
  28      bitwriter.Write(x, P);
  29  }
  30  
  31  template <typename IStream>
  32  uint64_t GolombRiceDecode(BitStreamReader<IStream>& bitreader, uint8_t P)
  33  {
  34      // Read unary-encoded quotient: q 1's followed by one 0.
  35      uint64_t q = 0;
  36      while (bitreader.Read(1) == 1) {
  37          ++q;
  38      }
  39  
  40      uint64_t r = bitreader.Read(P);
  41  
  42      return (q << P) + r;
  43  }
  44  
  45  #endif // BITCOIN_UTIL_GOLOMBRICE_H
  46