text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2014 The Bitcoin developers
  // Copyright (c) 2017-2019 The BITRUBCOIN developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_COMPRESSOR_H
  #define BITCOIN_COMPRESSOR_H
  
  #include "primitives/transaction.h"
  #include "script/script.h"
  #include "serialize.h"
  #include "span.h"
  
  bool CompressScript(const CScript& script, std::vector<unsigned char> &out);
  unsigned int GetSpecialScriptSize(unsigned int nSize);
  bool DecompressScript(CScript& script, unsigned int nSize, const std::vector<unsigned char> &out);
  
  uint64_t CompressAmount(uint64_t nAmount);
  uint64_t DecompressAmount(uint64_t nAmount);
  
  /** Compact serializer for scripts.
   *
   *  It detects common cases and encodes them much more efficiently.
   *  3 special cases are defined:
   *  * Pay to pubkey hash (encoded as 21 bytes)
   *  * Pay to script hash (encoded as 21 bytes)
   *  * Pay to pubkey starting with 0x02, 0x03 or 0x04 (encoded as 33 bytes)
   *
   *  Other scripts up to 121 bytes require 1 byte + script length. Above
   *  that, scripts up to 16505 bytes require 2 bytes + script length.
   */
  struct ScriptCompression
  {
      /**
       * make this static for now (there are only 6 special scripts defined)
       * this can potentially be extended together with a new nVersion for
       * transactions, in which case this value becomes dependent on nVersion
       * and nHeight of the enclosing transaction.
       */
      static const unsigned int nSpecialScripts = 6;
  
      template<typename Stream>
      void Ser(Stream &s, const CScript& script) {
          std::vector<unsigned char> compr;
          if (CompressScript(script, compr)) {
              s << MakeSpan(compr);
              return;
          }
          unsigned int nSize = script.size() + nSpecialScripts;
          s << VARINT(nSize);
          s << MakeSpan(script);
      }
  
      template<typename Stream>
      void Unser(Stream &s, CScript& script) {
          unsigned int nSize = 0;
          s >> VARINT(nSize);
          if (nSize < nSpecialScripts) {
              std::vector<unsigned char> vch(GetSpecialScriptSize(nSize), 0x00);
              s >> MakeSpan(vch);
              DecompressScript(script, nSize, vch);
              return;
          }
          nSize -= nSpecialScripts;
          if (nSize > MAX_SCRIPT_SIZE) {
              // Overly long script, replace with a short invalid one
              script << OP_RETURN;
              s.ignore(nSize);
          } else {
              script.resize(nSize);
              s >> MakeSpan(script);
          }
      }
  };
  
  struct AmountCompression
  {
      template<typename Stream, typename I> void Ser(Stream& s, I val)
      {
          s << VARINT(CompressAmount(val));
      }
      template<typename Stream, typename I> void Unser(Stream& s, I& val)
      {
          uint64_t v;
          s >> VARINT(v);
          val = DecompressAmount(v);
      }
  };
  
  /** wrapper for CTxOut that provides a more compact serialization */
  struct TxOutCompression
  {
      FORMATTER_METHODS(CTxOut, obj) { READWRITE(Using<AmountCompression>(obj.nValue), Using<ScriptCompression>(obj.scriptPubKey)); }
  };
  
  #endif // BITCOIN_COMPRESSOR_H
  