text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2014 The Bitcoin developers
  // Copyright (c) 2017-2019 The PIVX developers
  // Copyright (c) 2021 The NEUTRON Core 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"
  
  class CKeyID;
  class CPubKey;
  class CScriptID;
  
  /** 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.
   */
  class CScriptCompressor
  {
  private:
      /**
       * 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;
  
      CScript& script;
  
  protected:
      /**
       * These check for scripts for which a special case with a shorter encoding is defined.
       * They are implemented separately from the CScript test, as these test for exact byte
       * sequence correspondences, and are more strict. For example, IsToPubKey also verifies
       * whether the public key is valid (as invalid ones cannot be represented in compressed
       * form).
       */
      bool IsToKeyID(CKeyID& hash) const;
      bool IsToScriptID(CScriptID& hash) const;
      bool IsToPubKey(CPubKey& pubkey) const;
  
      bool Compress(std::vector<unsigned char>& out) const;
      unsigned int GetSpecialSize(unsigned int nSize) const;
      bool Decompress(unsigned int nSize, const std::vector<unsigned char>& out);
  
  public:
      CScriptCompressor(CScript& scriptIn) : script(scriptIn) {}
  
      template <typename Stream>
      void Serialize(Stream& s) const
      {
          std::vector<unsigned char> compr;
          if (Compress(compr)) {
              s << CFlatData(compr);
              return;
          }
          unsigned int nSize = script.size() + nSpecialScripts;
          s << VARINT(nSize);
          s << CFlatData(script);
      }
  
      template <typename Stream>
      void Unserialize(Stream& s)
      {
          unsigned int nSize = 0;
          s >> VARINT(nSize);
          if (nSize < nSpecialScripts) {
              std::vector<unsigned char> vch(GetSpecialSize(nSize), 0x00);
              s >> REF(CFlatData(vch));
              Decompress(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 >> REF(CFlatData(script));
          }
      }
  };
  
  /** wrapper for CTxOut that provides a more compact serialization */
  class CTxOutCompressor
  {
  private:
      CTxOut& txout;
  
  public:
      static uint64_t CompressAmount(uint64_t nAmount);
      static uint64_t DecompressAmount(uint64_t nAmount);
  
      CTxOutCompressor(CTxOut& txoutIn) : txout(txoutIn) {}
  
      ADD_SERIALIZE_METHODS;
  
      template <typename Stream, typename Operation>
      inline void SerializationOp(Stream& s, Operation ser_action)
      {
          if (!ser_action.ForRead()) {
              uint64_t nVal = CompressAmount(txout.nValue);
              READWRITE(VARINT(nVal));
          } else {
              uint64_t nVal = 0;
              READWRITE(VARINT(nVal));
              txout.nValue = DecompressAmount(nVal);
          }
          CScriptCompressor cscript(REF(txout.scriptPubKey));
          READWRITE(cscript);
      }
  };
  
  #endif // BITCOIN_COMPRESSOR_H
  