text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2016 The Bitcoin Core developers
  // Copyright (c) 2017 The Pigeon Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include "interpreter.h"
  
  #include "primitives/transaction.h"
  #include "crypto/ripemd160.h"
  #include "crypto/sha1.h"
  #include "crypto/sha256.h"
  #include "pubkey.h"
  #include "script/script.h"
  #include "uint256.h"
  
  typedef std::vector<unsigned char> valtype;
  
  namespace {
  
  inline bool set_success(ScriptError* ret)
  {
      if (ret)
          *ret = SCRIPT_ERR_OK;
      return true;
  }
  
  inline bool set_error(ScriptError* ret, const ScriptError serror)
  {
      if (ret)
          *ret = serror;
      return false;
  }
  
  } // namespace
  
  bool CastToBool(const valtype& vch)
  {
      for (unsigned int i = 0; i < vch.size(); i++)
      {
          if (vch[i] != 0)
          {
              // Can be negative zero
              if (i == vch.size()-1 && vch[i] == 0x80)
                  return false;
              return true;
          }
      }
      return false;
  }
  
  /**
   * Script is a stack machine (like Forth) that evaluates a predicate
   * returning a bool indicating valid or not.  There are no loops.
   */
  #define stacktop(i)  (stack.at(stack.size()+(i)))
  #define altstacktop(i)  (altstack.at(altstack.size()+(i)))
  static inline void popstack(std::vector<valtype>& stack)
  {
      if (stack.empty())
          throw std::runtime_error("popstack(): stack empty");
      stack.pop_back();
  }
  
  bool static IsCompressedOrUncompressedPubKey(const valtype &vchPubKey) {
      if (vchPubKey.size() < 33) {
          //  Non-canonical public key: too short
          return false;
      }
      if (vchPubKey[0] == 0x04) {
          if (vchPubKey.size() != 65) {
              //  Non-canonical public key: invalid length for uncompressed key
              return false;
          }
      } else if (vchPubKey[0] == 0x02 || vchPubKey[0] == 0x03) {
          if (vchPubKey.size() != 33) {
              //  Non-canonical public key: invalid length for compressed key
              return false;
          }
      } else {
          //  Non-canonical public key: neither compressed nor uncompressed
          return false;
      }
      return true;
  }
  
  bool static IsCompressedPubKey(const valtype &vchPubKey) {
      if (vchPubKey.size() != 33) {
          //  Non-canonical public key: invalid length for compressed key
          return false;
      }
      if (vchPubKey[0] != 0x02 && vchPubKey[0] != 0x03) {
          //  Non-canonical public key: invalid prefix for compressed key
          return false;
      }
      return true;
  }
  
  /**
   * A canonical signature exists of: <30> <total len> <02> <len R> <R> <02> <len S> <S> <hashtype>
   * Where R and S are not negative (their first byte has its highest bit not set), and not
   * excessively padded (do not start with a 0 byte, unless an otherwise negative number follows,
   * in which case a single 0 byte is necessary and even required).
   * 
   * See https://pigeontalk.org/index.php?topic=8392.msg127623#msg127623
   *
   * This function is consensus-critical since BIP66.
   */
  bool static IsValidSignatureEncoding(const std::vector<unsigned char> &sig) {
      // Format: 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S] [sighash]
      // * total-length: 1-byte length descriptor of everything that follows,
      //   excluding the sighash byte.
      // * R-length: 1-byte length descriptor of the R value that follows.
      // * R: arbitrary-length big-endian encoded R value. It must use the shortest
      //   possible encoding for a positive integers (which means no null bytes at
      //   the start, except a single one when the next byte has its highest bit set).
      // * S-length: 1-byte length descriptor of the S value that follows.
      // * S: arbitrary-length big-endian encoded S value. The same rules apply.
      // * sighash: 1-byte value indicating what data is hashed (not part of the DER
      //   signature)
  
      // Minimum and maximum size constraints.
      if (sig.size() < 9) return false;
      if (sig.size() > 73) return false;
  
      // A signature is of type 0x30 (compound).
      if (sig[0] != 0x30) return false;
  
      // Make sure the length covers the entire signature.
      if (sig[1] != sig.size() - 3) return false;
  
      // Extract the length of the R element.
      unsigned int lenR = sig[3];
  
      // Make sure the length of the S element is still inside the signature.
      if (5 + lenR >= sig.size()) return false;
  
      // Extract the length of the S element.
      unsigned int lenS = sig[5 + lenR];
  
      // Verify that the length of the signature matches the sum of the length
      // of the elements.
      if ((size_t)(lenR + lenS + 7) != sig.size()) return false;
   
      // Check whether the R element is an integer.
      if (sig[2] != 0x02) return false;
  
      // Zero-length integers are not allowed for R.
      if (lenR == 0) return false;
  
      // Negative numbers are not allowed for R.
      if (sig[4] & 0x80) return false;
  
      // Null bytes at the start of R are not allowed, unless R would
      // otherwise be interpreted as a negative number.
      if (lenR > 1 && (sig[4] == 0x00) && !(sig[5] & 0x80)) return false;
  
      // Check whether the S element is an integer.
      if (sig[lenR + 4] != 0x02) return false;
  
      // Zero-length integers are not allowed for S.
      if (lenS == 0) return false;
  
      // Negative numbers are not allowed for S.
      if (sig[lenR + 6] & 0x80) return false;
  
      // Null bytes at the start of S are not allowed, unless S would otherwise be
      // interpreted as a negative number.
      if (lenS > 1 && (sig[lenR + 6] == 0x00) && !(sig[lenR + 7] & 0x80)) return false;
  
      return true;
  }
  
  bool static IsLowDERSignature(const valtype &vchSig, ScriptError* serror) {
      if (!IsValidSignatureEncoding(vchSig)) {
          return set_error(serror, SCRIPT_ERR_SIG_DER);
      }
      std::vector<unsigned char> vchSigCopy(vchSig.begin(), vchSig.begin() + vchSig.size() - 1);
      if (!CPubKey::CheckLowS(vchSigCopy)) {
          return set_error(serror, SCRIPT_ERR_SIG_HIGH_S);
      }
      return true;
  }
  
  bool static IsDefinedHashtypeSignature(const valtype &vchSig) {
      if (vchSig.size() == 0) {
          return false;
      }
      unsigned char nHashType = vchSig[vchSig.size() - 1] & (~(SIGHASH_ANYONECANPAY));
      if (nHashType < SIGHASH_ALL || nHashType > SIGHASH_SINGLE)
          return false;
  
      return true;
  }
  
  bool CheckSignatureEncoding(const std::vector<unsigned char> &vchSig, unsigned int flags, ScriptError* serror) {
      // Empty signature. Not strictly DER encoded, but allowed to provide a
      // compact way to provide an invalid signature for use with CHECK(MULTI)SIG
      if (vchSig.size() == 0) {
          return true;
      }
      if ((flags & (SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S | SCRIPT_VERIFY_STRICTENC)) != 0 && !IsValidSignatureEncoding(vchSig)) {
          return set_error(serror, SCRIPT_ERR_SIG_DER);
      } else if ((flags & SCRIPT_VERIFY_LOW_S) != 0 && !IsLowDERSignature(vchSig, serror)) {
          // serror is set
          return false;
      } else if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 && !IsDefinedHashtypeSignature(vchSig)) {
          return set_error(serror, SCRIPT_ERR_SIG_HASHTYPE);
      }
      return true;
  }
  
  bool static CheckPubKeyEncoding(const valtype &vchPubKey, unsigned int flags, const SigVersion &sigversion, ScriptError* serror) {
      if ((flags & SCRIPT_VERIFY_STRICTENC) != 0 && !IsCompressedOrUncompressedPubKey(vchPubKey)) {
          return set_error(serror, SCRIPT_ERR_PUBKEYTYPE);
      }
      // Only compressed keys are accepted in segwit
      if ((flags & SCRIPT_VERIFY_WITNESS_PUBKEYTYPE) != 0 && sigversion == SIGVERSION_WITNESS_V0 && !IsCompressedPubKey(vchPubKey)) {
          return set_error(serror, SCRIPT_ERR_WITNESS_PUBKEYTYPE);
      }
      return true;
  }
  
  bool static CheckMinimalPush(const valtype& data, opcodetype opcode) {
      if (data.size() == 0) {
          // Could have used OP_0.
          return opcode == OP_0;
      } else if (data.size() == 1 && data[0] >= 1 && data[0] <= 16) {
          // Could have used OP_1 .. OP_16.
          return opcode == OP_1 + (data[0] - 1);
      } else if (data.size() == 1 && data[0] == 0x81) {
          // Could have used OP_1NEGATE.
          return opcode == OP_1NEGATE;
      } else if (data.size() <= 75) {
          // Could have used a direct push (opcode indicating number of bytes pushed + those bytes).
          return opcode == data.size();
      } else if (data.size() <= 255) {
          // Could have used OP_PUSHDATA.
          return opcode == OP_PUSHDATA1;
      } else if (data.size() <= 65535) {
          // Could have used OP_PUSHDATA2.
          return opcode == OP_PUSHDATA2;
      }
      return true;
  }
  
  bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* serror)
  {
      static const CScriptNum bnZero(0);
      static const CScriptNum bnOne(1);
      // static const CScriptNum bnFalse(0);
      // static const CScriptNum bnTrue(1);
      static const valtype vchFalse(0);
      // static const valtype vchZero(0);
      static const valtype vchTrue(1, 1);
  
      CScript::const_iterator pc = script.begin();
      CScript::const_iterator pend = script.end();
      CScript::const_iterator pbegincodehash = script.begin();
      opcodetype opcode;
      valtype vchPushValue;
      std::vector<bool> vfExec;
      std::vector<valtype> altstack;
      set_error(serror, SCRIPT_ERR_UNKNOWN_ERROR);
      if (script.size() > MAX_SCRIPT_SIZE)
          return set_error(serror, SCRIPT_ERR_SCRIPT_SIZE);
      int nOpCount = 0;
      bool fRequireMinimal = (flags & SCRIPT_VERIFY_MINIMALDATA) != 0;
  
      try
      {
          while (pc < pend)
          {
              bool fExec = !count(vfExec.begin(), vfExec.end(), false);
  
              //
              // Read instruction
              //
              if (!script.GetOp(pc, opcode, vchPushValue))
                  return set_error(serror, SCRIPT_ERR_BAD_OPCODE);
              if (vchPushValue.size() > MAX_SCRIPT_ELEMENT_SIZE)
                  return set_error(serror, SCRIPT_ERR_PUSH_SIZE);
  
              // Note how OP_RESERVED does not count towards the opcode limit.
              if (opcode > OP_16 && ++nOpCount > MAX_OPS_PER_SCRIPT)
                  return set_error(serror, SCRIPT_ERR_OP_COUNT);
  
              if (opcode == OP_CAT ||
                  opcode == OP_SUBSTR ||
                  opcode == OP_LEFT ||
                  opcode == OP_RIGHT ||
                  opcode == OP_INVERT ||
                  opcode == OP_AND ||
                  opcode == OP_OR ||
                  opcode == OP_XOR ||
                  opcode == OP_2MUL ||
                  opcode == OP_2DIV ||
                  opcode == OP_MUL ||
                  opcode == OP_DIV ||
                  opcode == OP_MOD ||
                  opcode == OP_LSHIFT ||
                  opcode == OP_RSHIFT)
                  return set_error(serror, SCRIPT_ERR_DISABLED_OPCODE); // Disabled opcodes.
  
              if (fExec && 0 <= opcode && opcode <= OP_PUSHDATA4) {
                  if (fRequireMinimal && !CheckMinimalPush(vchPushValue, opcode)) {
                      return set_error(serror, SCRIPT_ERR_MINIMALDATA);
                  }
                  stack.push_back(vchPushValue);
              } else if (fExec || (OP_IF <= opcode && opcode <= OP_ENDIF))
              switch (opcode)
              {
                  //
                  // Push value
                  //
                  case OP_1NEGATE:
                  case OP_1:
                  case OP_2:
                  case OP_3:
                  case OP_4:
                  case OP_5:
                  case OP_6:
                  case OP_7:
                  case OP_8:
                  case OP_9:
                  case OP_10:
                  case OP_11:
                  case OP_12:
                  case OP_13:
                  case OP_14:
                  case OP_15:
                  case OP_16:
                  {
                      // ( -- value)
                      CScriptNum bn((int)opcode - (int)(OP_1 - 1));
                      stack.push_back(bn.getvch());
                      // The result of these opcodes should always be the minimal way to push the data
                      // they push, so no need for a CheckMinimalPush here.
                  }
                  break;
  
  
                  //
                  // Control
                  //
                  case OP_NOP:
                      break;
  
                  case OP_CHECKLOCKTIMEVERIFY:
                  {
                      if (!(flags & SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY)) {
                          // not enabled; treat as a NOP2
                          if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
                              return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
                          }
                          break;
                      }
  
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
  
                      // Note that elsewhere numeric opcodes are limited to
                      // operands in the range -2**31+1 to 2**31-1, however it is
                      // legal for opcodes to produce results exceeding that
                      // range. This limitation is implemented by CScriptNum's
                      // default 4-byte limit.
                      //
                      // If we kept to that limit we'd have a year 2038 problem,
                      // even though the nLockTime field in transactions
                      // themselves is uint32 which only becomes meaningless
                      // after the year 2106.
                      //
                      // Thus as a special case we tell CScriptNum to accept up
                      // to 5-byte bignums, which are good until 2**39-1, well
                      // beyond the 2**32-1 limit of the nLockTime field itself.
                      const CScriptNum nLockTime(stacktop(-1), fRequireMinimal, 5);
  
                      // In the rare event that the argument may be < 0 due to
                      // some arithmetic being done first, you can always use
                      // 0 MAX CHECKLOCKTIMEVERIFY.
                      if (nLockTime < 0)
                          return set_error(serror, SCRIPT_ERR_NEGATIVE_LOCKTIME);
  
                      // Actually compare the specified lock time with the transaction.
                      if (!checker.CheckLockTime(nLockTime))
                          return set_error(serror, SCRIPT_ERR_UNSATISFIED_LOCKTIME);
  
                      break;
                  }
  
                  case OP_CHECKSEQUENCEVERIFY:
                  {
                      if (!(flags & SCRIPT_VERIFY_CHECKSEQUENCEVERIFY)) {
                          // not enabled; treat as a NOP3
                          if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
                              return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
                          }
                          break;
                      }
  
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
  
                      // nSequence, like nLockTime, is a 32-bit unsigned integer
                      // field. See the comment in CHECKLOCKTIMEVERIFY regarding
                      // 5-byte numeric operands.
                      const CScriptNum nSequence(stacktop(-1), fRequireMinimal, 5);
  
                      // In the rare event that the argument may be < 0 due to
                      // some arithmetic being done first, you can always use
                      // 0 MAX CHECKSEQUENCEVERIFY.
                      if (nSequence < 0)
                          return set_error(serror, SCRIPT_ERR_NEGATIVE_LOCKTIME);
  
                      // To provide for future soft-fork extensibility, if the
                      // operand has the disabled lock-time flag set,
                      // CHECKSEQUENCEVERIFY behaves as a NOP.
                      if ((nSequence & CTxIn::SEQUENCE_LOCKTIME_DISABLE_FLAG) != 0)
                          break;
  
                      // Compare the specified sequence number with the input.
                      if (!checker.CheckSequence(nSequence))
                          return set_error(serror, SCRIPT_ERR_UNSATISFIED_LOCKTIME);
  
                      break;
                  }
  
                  case OP_NOP1: case OP_NOP4: case OP_NOP5:
                  case OP_NOP6: case OP_NOP7: case OP_NOP8: case OP_NOP9: case OP_NOP10:
                  {
                      if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS)
                          return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
                  }
                  break;
  
                  case OP_IF:
                  case OP_NOTIF:
                  {
                      // <expression> if [statements] [else [statements]] endif
                      bool fValue = false;
                      if (fExec)
                      {
                          if (stack.size() < 1)
                              return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
                          valtype& vch = stacktop(-1);
                          if (sigversion == SIGVERSION_WITNESS_V0 && (flags & SCRIPT_VERIFY_MINIMALIF)) {
                              if (vch.size() > 1)
                                  return set_error(serror, SCRIPT_ERR_MINIMALIF);
                              if (vch.size() == 1 && vch[0] != 1)
                                  return set_error(serror, SCRIPT_ERR_MINIMALIF);
                          }
                          fValue = CastToBool(vch);
                          if (opcode == OP_NOTIF)
                              fValue = !fValue;
                          popstack(stack);
                      }
                      vfExec.push_back(fValue);
                  }
                  break;
  
                  case OP_ELSE:
                  {
                      if (vfExec.empty())
                          return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
                      vfExec.back() = !vfExec.back();
                  }
                  break;
  
                  case OP_ENDIF:
                  {
                      if (vfExec.empty())
                          return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
                      vfExec.pop_back();
                  }
                  break;
  
                  case OP_VERIFY:
                  {
                      // (true -- ) or
                      // (false -- false) and return
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      bool fValue = CastToBool(stacktop(-1));
                      if (fValue)
                          popstack(stack);
                      else
                          return set_error(serror, SCRIPT_ERR_VERIFY);
                  }
                  break;
  
                  case OP_RETURN:
                  {
                      return set_error(serror, SCRIPT_ERR_OP_RETURN);
                  }
                  break;
  
  
                  //
                  // Stack ops
                  //
                  case OP_TOALTSTACK:
                  {
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      altstack.push_back(stacktop(-1));
                      popstack(stack);
                  }
                  break;
  
                  case OP_FROMALTSTACK:
                  {
                      if (altstack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_ALTSTACK_OPERATION);
                      stack.push_back(altstacktop(-1));
                      popstack(altstack);
                  }
                  break;
  
                  case OP_2DROP:
                  {
                      // (x1 x2 -- )
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      popstack(stack);
                      popstack(stack);
                  }
                  break;
  
                  case OP_2DUP:
                  {
                      // (x1 x2 -- x1 x2 x1 x2)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch1 = stacktop(-2);
                      valtype vch2 = stacktop(-1);
                      stack.push_back(vch1);
                      stack.push_back(vch2);
                  }
                  break;
  
                  case OP_3DUP:
                  {
                      // (x1 x2 x3 -- x1 x2 x3 x1 x2 x3)
                      if (stack.size() < 3)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch1 = stacktop(-3);
                      valtype vch2 = stacktop(-2);
                      valtype vch3 = stacktop(-1);
                      stack.push_back(vch1);
                      stack.push_back(vch2);
                      stack.push_back(vch3);
                  }
                  break;
  
                  case OP_2OVER:
                  {
                      // (x1 x2 x3 x4 -- x1 x2 x3 x4 x1 x2)
                      if (stack.size() < 4)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch1 = stacktop(-4);
                      valtype vch2 = stacktop(-3);
                      stack.push_back(vch1);
                      stack.push_back(vch2);
                  }
                  break;
  
                  case OP_2ROT:
                  {
                      // (x1 x2 x3 x4 x5 x6 -- x3 x4 x5 x6 x1 x2)
                      if (stack.size() < 6)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch1 = stacktop(-6);
                      valtype vch2 = stacktop(-5);
                      stack.erase(stack.end()-6, stack.end()-4);
                      stack.push_back(vch1);
                      stack.push_back(vch2);
                  }
                  break;
  
                  case OP_2SWAP:
                  {
                      // (x1 x2 x3 x4 -- x3 x4 x1 x2)
                      if (stack.size() < 4)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      swap(stacktop(-4), stacktop(-2));
                      swap(stacktop(-3), stacktop(-1));
                  }
                  break;
  
                  case OP_IFDUP:
                  {
                      // (x - 0 | x x)
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch = stacktop(-1);
                      if (CastToBool(vch))
                          stack.push_back(vch);
                  }
                  break;
  
                  case OP_DEPTH:
                  {
                      // -- stacksize
                      CScriptNum bn(stack.size());
                      stack.push_back(bn.getvch());
                  }
                  break;
  
                  case OP_DROP:
                  {
                      // (x -- )
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      popstack(stack);
                  }
                  break;
  
                  case OP_DUP:
                  {
                      // (x -- x x)
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch = stacktop(-1);
                      stack.push_back(vch);
                  }
                  break;
  
                  case OP_NIP:
                  {
                      // (x1 x2 -- x2)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      stack.erase(stack.end() - 2);
                  }
                  break;
  
                  case OP_OVER:
                  {
                      // (x1 x2 -- x1 x2 x1)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch = stacktop(-2);
                      stack.push_back(vch);
                  }
                  break;
  
                  case OP_PICK:
                  case OP_ROLL:
                  {
                      // (xn ... x2 x1 x0 n - xn ... x2 x1 x0 xn)
                      // (xn ... x2 x1 x0 n - ... x2 x1 x0 xn)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      int n = CScriptNum(stacktop(-1), fRequireMinimal).getint();
                      popstack(stack);
                      if (n < 0 || n >= (int)stack.size())
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch = stacktop(-n-1);
                      if (opcode == OP_ROLL)
                          stack.erase(stack.end()-n-1);
                      stack.push_back(vch);
                  }
                  break;
  
                  case OP_ROT:
                  {
                      // (x1 x2 x3 -- x2 x3 x1)
                      //  x2 x1 x3  after first swap
                      //  x2 x3 x1  after second swap
                      if (stack.size() < 3)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      swap(stacktop(-3), stacktop(-2));
                      swap(stacktop(-2), stacktop(-1));
                  }
                  break;
  
                  case OP_SWAP:
                  {
                      // (x1 x2 -- x2 x1)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      swap(stacktop(-2), stacktop(-1));
                  }
                  break;
  
                  case OP_TUCK:
                  {
                      // (x1 x2 -- x2 x1 x2)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype vch = stacktop(-1);
                      stack.insert(stack.end()-2, vch);
                  }
                  break;
  
  
                  case OP_SIZE:
                  {
                      // (in -- in size)
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      CScriptNum bn(stacktop(-1).size());
                      stack.push_back(bn.getvch());
                  }
                  break;
  
  
                  //
                  // Bitwise logic
                  //
                  case OP_EQUAL:
                  case OP_EQUALVERIFY:
                  //case OP_NOTEQUAL: // use OP_NUMNOTEQUAL
                  {
                      // (x1 x2 - bool)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype& vch1 = stacktop(-2);
                      valtype& vch2 = stacktop(-1);
                      bool fEqual = (vch1 == vch2);
                      // OP_NOTEQUAL is disabled because it would be too easy to say
                      // something like n != 1 and have some wiseguy pass in 1 with extra
                      // zero bytes after it (numerically, 0x01 == 0x0001 == 0x000001)
                      //if (opcode == OP_NOTEQUAL)
                      //    fEqual = !fEqual;
                      popstack(stack);
                      popstack(stack);
                      stack.push_back(fEqual ? vchTrue : vchFalse);
                      if (opcode == OP_EQUALVERIFY)
                      {
                          if (fEqual)
                              popstack(stack);
                          else
                              return set_error(serror, SCRIPT_ERR_EQUALVERIFY);
                      }
                  }
                  break;
  
  
                  //
                  // Numeric
                  //
                  case OP_1ADD:
                  case OP_1SUB:
                  case OP_NEGATE:
                  case OP_ABS:
                  case OP_NOT:
                  case OP_0NOTEQUAL:
                  {
                      // (in -- out)
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      CScriptNum bn(stacktop(-1), fRequireMinimal);
                      switch (opcode)
                      {
                      case OP_1ADD:       bn += bnOne; break;
                      case OP_1SUB:       bn -= bnOne; break;
                      case OP_NEGATE:     bn = -bn; break;
                      case OP_ABS:        if (bn < bnZero) bn = -bn; break;
                      case OP_NOT:        bn = (bn == bnZero); break;
                      case OP_0NOTEQUAL:  bn = (bn != bnZero); break;
                      default:            assert(!"invalid opcode"); break;
                      }
                      popstack(stack);
                      stack.push_back(bn.getvch());
                  }
                  break;
  
                  case OP_ADD:
                  case OP_SUB:
                  case OP_BOOLAND:
                  case OP_BOOLOR:
                  case OP_NUMEQUAL:
                  case OP_NUMEQUALVERIFY:
                  case OP_NUMNOTEQUAL:
                  case OP_LESSTHAN:
                  case OP_GREATERTHAN:
                  case OP_LESSTHANOREQUAL:
                  case OP_GREATERTHANOREQUAL:
                  case OP_MIN:
                  case OP_MAX:
                  {
                      // (x1 x2 -- out)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      CScriptNum bn1(stacktop(-2), fRequireMinimal);
                      CScriptNum bn2(stacktop(-1), fRequireMinimal);
                      CScriptNum bn(0);
                      switch (opcode)
                      {
                      case OP_ADD:
                          bn = bn1 + bn2;
                          break;
  
                      case OP_SUB:
                          bn = bn1 - bn2;
                          break;
  
                      case OP_BOOLAND:             bn = (bn1 != bnZero && bn2 != bnZero); break;
                      case OP_BOOLOR:              bn = (bn1 != bnZero || bn2 != bnZero); break;
                      case OP_NUMEQUAL:            bn = (bn1 == bn2); break;
                      case OP_NUMEQUALVERIFY:      bn = (bn1 == bn2); break;
                      case OP_NUMNOTEQUAL:         bn = (bn1 != bn2); break;
                      case OP_LESSTHAN:            bn = (bn1 < bn2); break;
                      case OP_GREATERTHAN:         bn = (bn1 > bn2); break;
                      case OP_LESSTHANOREQUAL:     bn = (bn1 <= bn2); break;
                      case OP_GREATERTHANOREQUAL:  bn = (bn1 >= bn2); break;
                      case OP_MIN:                 bn = (bn1 < bn2 ? bn1 : bn2); break;
                      case OP_MAX:                 bn = (bn1 > bn2 ? bn1 : bn2); break;
                      default:                     assert(!"invalid opcode"); break;
                      }
                      popstack(stack);
                      popstack(stack);
                      stack.push_back(bn.getvch());
  
                      if (opcode == OP_NUMEQUALVERIFY)
                      {
                          if (CastToBool(stacktop(-1)))
                              popstack(stack);
                          else
                              return set_error(serror, SCRIPT_ERR_NUMEQUALVERIFY);
                      }
                  }
                  break;
  
                  case OP_WITHIN:
                  {
                      // (x min max -- out)
                      if (stack.size() < 3)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      CScriptNum bn1(stacktop(-3), fRequireMinimal);
                      CScriptNum bn2(stacktop(-2), fRequireMinimal);
                      CScriptNum bn3(stacktop(-1), fRequireMinimal);
                      bool fValue = (bn2 <= bn1 && bn1 < bn3);
                      popstack(stack);
                      popstack(stack);
                      popstack(stack);
                      stack.push_back(fValue ? vchTrue : vchFalse);
                  }
                  break;
  
  
                  //
                  // Crypto
                  //
                  case OP_RIPEMD160:
                  case OP_SHA1:
                  case OP_SHA256:
                  case OP_HASH160:
                  case OP_HASH256:
                  {
                      // (in -- hash)
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      valtype& vch = stacktop(-1);
                      valtype vchHash((opcode == OP_RIPEMD160 || opcode == OP_SHA1 || opcode == OP_HASH160) ? 20 : 32);
                      if (opcode == OP_RIPEMD160)
                          CRIPEMD160().Write(vch.data(), vch.size()).Finalize(vchHash.data());
                      else if (opcode == OP_SHA1)
                          CSHA1().Write(vch.data(), vch.size()).Finalize(vchHash.data());
                      else if (opcode == OP_SHA256)
                          CSHA256().Write(vch.data(), vch.size()).Finalize(vchHash.data());
                      else if (opcode == OP_HASH160)
                          CHash160().Write(vch.data(), vch.size()).Finalize(vchHash.data());
                      else if (opcode == OP_HASH256)
                          CHash256().Write(vch.data(), vch.size()).Finalize(vchHash.data());
                      popstack(stack);
                      stack.push_back(vchHash);
                  }
                  break;                                   
  
                  case OP_CODESEPARATOR:
                  {
                      // Hash starts after the code separator
                      pbegincodehash = pc;
                  }
                  break;
  
                  case OP_CHECKSIG:
                  case OP_CHECKSIGVERIFY:
                  {
                      // (sig pubkey -- bool)
                      if (stack.size() < 2)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
  
                      valtype& vchSig    = stacktop(-2);
                      valtype& vchPubKey = stacktop(-1);
  
                      // Subset of script starting at the most recent codeseparator
                      CScript scriptCode(pbegincodehash, pend);
  
                      // Drop the signature in pre-segwit scripts but not segwit scripts
                      if (sigversion == SIGVERSION_BASE) {
                          scriptCode.FindAndDelete(CScript(vchSig));
                      }
  
                      if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, sigversion, serror)) {
                          //serror is set
                          return false;
                      }
                      bool fSuccess = checker.CheckSig(vchSig, vchPubKey, scriptCode, sigversion);
  
                      if (!fSuccess && (flags & SCRIPT_VERIFY_NULLFAIL) && vchSig.size())
                          return set_error(serror, SCRIPT_ERR_SIG_NULLFAIL);
  
                      popstack(stack);
                      popstack(stack);
                      stack.push_back(fSuccess ? vchTrue : vchFalse);
                      if (opcode == OP_CHECKSIGVERIFY)
                      {
                          if (fSuccess)
                              popstack(stack);
                          else
                              return set_error(serror, SCRIPT_ERR_CHECKSIGVERIFY);
                      }
                  }
                  break;
  
                  case OP_CHECKMULTISIG:
                  case OP_CHECKMULTISIGVERIFY:
                  {
                      // ([sig ...] num_of_signatures [pubkey ...] num_of_pubkeys -- bool)
  
                      int i = 1;
                      if ((int)stack.size() < i)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
  
                      int nKeysCount = CScriptNum(stacktop(-i), fRequireMinimal).getint();
                      if (nKeysCount < 0 || nKeysCount > MAX_PUBKEYS_PER_MULTISIG)
                          return set_error(serror, SCRIPT_ERR_PUBKEY_COUNT);
                      nOpCount += nKeysCount;
                      if (nOpCount > MAX_OPS_PER_SCRIPT)
                          return set_error(serror, SCRIPT_ERR_OP_COUNT);
                      int ikey = ++i;
                      // ikey2 is the position of last non-signature item in the stack. Top stack item = 1.
                      // With SCRIPT_VERIFY_NULLFAIL, this is used for cleanup if operation fails.
                      int ikey2 = nKeysCount + 2;
                      i += nKeysCount;
                      if ((int)stack.size() < i)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
  
                      int nSigsCount = CScriptNum(stacktop(-i), fRequireMinimal).getint();
                      if (nSigsCount < 0 || nSigsCount > nKeysCount)
                          return set_error(serror, SCRIPT_ERR_SIG_COUNT);
                      int isig = ++i;
                      i += nSigsCount;
                      if ((int)stack.size() < i)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
  
                      // Subset of script starting at the most recent codeseparator
                      CScript scriptCode(pbegincodehash, pend);
  
                      // Drop the signature in pre-segwit scripts but not segwit scripts
                      for (int k = 0; k < nSigsCount; k++)
                      {
                          valtype& vchSig = stacktop(-isig-k);
                          if (sigversion == SIGVERSION_BASE) {
                              scriptCode.FindAndDelete(CScript(vchSig));
                          }
                      }
  
                      bool fSuccess = true;
                      while (fSuccess && nSigsCount > 0)
                      {
                          valtype& vchSig    = stacktop(-isig);
                          valtype& vchPubKey = stacktop(-ikey);
  
                          // Note how this makes the exact order of pubkey/signature evaluation
                          // distinguishable by CHECKMULTISIG NOT if the STRICTENC flag is set.
                          // See the script_(in)valid tests for details.
                          if (!CheckSignatureEncoding(vchSig, flags, serror) || !CheckPubKeyEncoding(vchPubKey, flags, sigversion, serror)) {
                              // serror is set
                              return false;
                          }
  
                          // Check signature
                          bool fOk = checker.CheckSig(vchSig, vchPubKey, scriptCode, sigversion);
  
                          if (fOk) {
                              isig++;
                              nSigsCount--;
                          }
                          ikey++;
                          nKeysCount--;
  
                          // If there are more signatures left than keys left,
                          // then too many signatures have failed. Exit early,
                          // without checking any further signatures.
                          if (nSigsCount > nKeysCount)
                              fSuccess = false;
                      }
  
                      // Clean up stack of actual arguments
                      while (i-- > 1) {
                          // If the operation failed, we require that all signatures must be empty vector
                          if (!fSuccess && (flags & SCRIPT_VERIFY_NULLFAIL) && !ikey2 && stacktop(-1).size())
                              return set_error(serror, SCRIPT_ERR_SIG_NULLFAIL);
                          if (ikey2 > 0)
                              ikey2--;
                          popstack(stack);
                      }
  
                      // A bug causes CHECKMULTISIG to consume one extra argument
                      // whose contents were not checked in any way.
                      //
                      // Unfortunately this is a potential source of mutability,
                      // so optionally verify it is exactly equal to zero prior
                      // to removing it from the stack.
                      if (stack.size() < 1)
                          return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
                      if ((flags & SCRIPT_VERIFY_NULLDUMMY) && stacktop(-1).size())
                          return set_error(serror, SCRIPT_ERR_SIG_NULLDUMMY);
                      popstack(stack);
  
                      stack.push_back(fSuccess ? vchTrue : vchFalse);
  
                      if (opcode == OP_CHECKMULTISIGVERIFY)
                      {
                          if (fSuccess)
                              popstack(stack);
                          else
                              return set_error(serror, SCRIPT_ERR_CHECKMULTISIGVERIFY);
                      }
                  }
                  break;
  
                  default:
                      return set_error(serror, SCRIPT_ERR_BAD_OPCODE);
              }
  
              // Size limits
              if (stack.size() + altstack.size() > MAX_STACK_SIZE)
                  return set_error(serror, SCRIPT_ERR_STACK_SIZE);
          }
      }
      catch (...)
      {
          return set_error(serror, SCRIPT_ERR_UNKNOWN_ERROR);
      }
  
      if (!vfExec.empty())
          return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
  
      return set_success(serror);
  }
  
  namespace {
  
  /**
   * Wrapper that serializes like CTransaction, but with the modifications
   *  required for the signature hash done in-place
   */
  class CTransactionSignatureSerializer {
  private:
      const CTransaction& txTo;  //!< reference to the spending transaction (the one being serialized)
      const CScript& scriptCode; //!< output script being consumed
      const unsigned int nIn;    //!< input index of txTo being signed
      const bool fAnyoneCanPay;  //!< whether the hashtype has the SIGHASH_ANYONECANPAY flag set
      const bool fHashSingle;    //!< whether the hashtype is SIGHASH_SINGLE
      const bool fHashNone;      //!< whether the hashtype is SIGHASH_NONE
  
  public:
      CTransactionSignatureSerializer(const CTransaction &txToIn, const CScript &scriptCodeIn, unsigned int nInIn, int nHashTypeIn) :
          txTo(txToIn), scriptCode(scriptCodeIn), nIn(nInIn),
          fAnyoneCanPay(!!(nHashTypeIn & SIGHASH_ANYONECANPAY)),
          fHashSingle((nHashTypeIn & 0x1f) == SIGHASH_SINGLE),
          fHashNone((nHashTypeIn & 0x1f) == SIGHASH_NONE) {}
  
      /** Serialize the passed scriptCode, skipping OP_CODESEPARATORs */
      template<typename S>
      void SerializeScriptCode(S &s) const {
          CScript::const_iterator it = scriptCode.begin();
          CScript::const_iterator itBegin = it;
          opcodetype opcode;
          unsigned int nCodeSeparators = 0;
          while (scriptCode.GetOp(it, opcode)) {
              if (opcode == OP_CODESEPARATOR)
                  nCodeSeparators++;
          }
          ::WriteCompactSize(s, scriptCode.size() - nCodeSeparators);
          it = itBegin;
          while (scriptCode.GetOp(it, opcode)) {
              if (opcode == OP_CODESEPARATOR) {
                  s.write((char*)&itBegin[0], it-itBegin-1);
                  itBegin = it;
              }
          }
          if (itBegin != scriptCode.end())
              s.write((char*)&itBegin[0], it-itBegin);
      }
  
      /** Serialize an input of txTo */
      template<typename S>
      void SerializeInput(S &s, unsigned int nInput) const {
          // In case of SIGHASH_ANYONECANPAY, only the input being signed is serialized
          if (fAnyoneCanPay)
              nInput = nIn;
          // Serialize the prevout
          ::Serialize(s, txTo.vin[nInput].prevout);
          // Serialize the script
          if (nInput != nIn)
              // Blank out other inputs' signatures
              ::Serialize(s, CScript());
          else
              SerializeScriptCode(s);
          // Serialize the nSequence
          if (nInput != nIn && (fHashSingle || fHashNone))
              // let the others update at will
              ::Serialize(s, (int)0);
          else
              ::Serialize(s, txTo.vin[nInput].nSequence);
      }
  
      /** Serialize an output of txTo */
      template<typename S>
      void SerializeOutput(S &s, unsigned int nOutput) const {
          if (fHashSingle && nOutput != nIn)
              // Do not lock-in the txout payee at other indices as txin
              ::Serialize(s, CTxOut());
          else
              ::Serialize(s, txTo.vout[nOutput]);
      }
  
      /** Serialize txTo */
      template<typename S>
      void Serialize(S &s) const {
          // Serialize nVersion
          ::Serialize(s, txTo.nVersion);
          // Serialize vin
          unsigned int nInputs = fAnyoneCanPay ? 1 : txTo.vin.size();
          ::WriteCompactSize(s, nInputs);
          for (unsigned int nInput = 0; nInput < nInputs; nInput++)
               SerializeInput(s, nInput);
          // Serialize vout
          unsigned int nOutputs = fHashNone ? 0 : (fHashSingle ? nIn+1 : txTo.vout.size());
          ::WriteCompactSize(s, nOutputs);
          for (unsigned int nOutput = 0; nOutput < nOutputs; nOutput++)
               SerializeOutput(s, nOutput);
          // Serialize nLockTime
          ::Serialize(s, txTo.nLockTime);
      }
  };
  
  uint256 GetPrevoutHash(const CTransaction& txTo) {
      CHashWriter ss(SER_GETHASH, 0);
      for (const auto& txin : txTo.vin) {
          ss << txin.prevout;
      }
      return ss.GetHash();
  }
  
  uint256 GetSequenceHash(const CTransaction& txTo) {
      CHashWriter ss(SER_GETHASH, 0);
      for (const auto& txin : txTo.vin) {
          ss << txin.nSequence;
      }
      return ss.GetHash();
  }
  
  uint256 GetOutputsHash(const CTransaction& txTo) {
      CHashWriter ss(SER_GETHASH, 0);
      for (const auto& txout : txTo.vout) {
          ss << txout;
      }
      return ss.GetHash();
  }
  
  } // namespace
  
  PrecomputedTransactionData::PrecomputedTransactionData(const CTransaction& txTo)
  {
      // Cache is calculated only for transactions with witness
      if (txTo.HasWitness()) {
          hashPrevouts = GetPrevoutHash(txTo);
          hashSequence = GetSequenceHash(txTo);
          hashOutputs = GetOutputsHash(txTo);
          ready = true;
      }
  }
  
  uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion, const PrecomputedTransactionData* cache)
  {
      assert(nIn < txTo.vin.size());
  
      if (sigversion == SIGVERSION_WITNESS_V0) {
          uint256 hashPrevouts;
          uint256 hashSequence;
          uint256 hashOutputs;
          const bool cacheready = cache && cache->ready;
  
          if (!(nHashType & SIGHASH_ANYONECANPAY)) {
              hashPrevouts = cacheready ? cache->hashPrevouts : GetPrevoutHash(txTo);
          }
  
          if (!(nHashType & SIGHASH_ANYONECANPAY) && (nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
              hashSequence = cacheready ? cache->hashSequence : GetSequenceHash(txTo);
          }
  
  
          if ((nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
              hashOutputs = cacheready ? cache->hashOutputs : GetOutputsHash(txTo);
          } else if ((nHashType & 0x1f) == SIGHASH_SINGLE && nIn < txTo.vout.size()) {
              CHashWriter ss(SER_GETHASH, 0);
              ss << txTo.vout[nIn];
              hashOutputs = ss.GetHash();
          }
  
          CHashWriter ss(SER_GETHASH, 0);
          // Version
          ss << txTo.nVersion;
          // Input prevouts/nSequence (none/all, depending on flags)
          ss << hashPrevouts;
          ss << hashSequence;
          // The input being signed (replacing the scriptSig with scriptCode + amount)
          // The prevout may already be contained in hashPrevout, and the nSequence
          // may already be contain in hashSequence.
          ss << txTo.vin[nIn].prevout;
          ss << scriptCode;
          ss << amount;
          ss << txTo.vin[nIn].nSequence;
          // Outputs (none/one/all, depending on flags)
          ss << hashOutputs;
          // Locktime
          ss << txTo.nLockTime;
          // Sighash type
          ss << nHashType;
  
          return ss.GetHash();
      }
  
      static const uint256 one(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
  
      // Check for invalid use of SIGHASH_SINGLE
      if ((nHashType & 0x1f) == SIGHASH_SINGLE) {
          if (nIn >= txTo.vout.size()) {
              //  nOut out of range
              return one;
          }
      }
  
      // Wrapper to serialize only the necessary parts of the transaction being signed
      CTransactionSignatureSerializer txTmp(txTo, scriptCode, nIn, nHashType);
  
      // Serialize and hash
      CHashWriter ss(SER_GETHASH, 0);
      ss << txTmp << nHashType;
      return ss.GetHash();
  }
  
  bool TransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
  {
      return pubkey.Verify(sighash, vchSig);
  }
  
  bool TransactionSignatureChecker::CheckSig(const std::vector<unsigned char>& vchSigIn, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const
  {
      CPubKey pubkey(vchPubKey);
      if (!pubkey.IsValid())
          return false;
  
      // Hash type is one byte tacked on to the end of the signature
      std::vector<unsigned char> vchSig(vchSigIn);
      if (vchSig.empty())
          return false;
      int nHashType = vchSig.back();
      vchSig.pop_back();
  
      uint256 sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion, this->txdata);
  
      if (!VerifySignature(vchSig, pubkey, sighash))
          return false;
  
      return true;
  }
  
  bool TransactionSignatureChecker::CheckLockTime(const CScriptNum& nLockTime) const
  {
      // There are two kinds of nLockTime: lock-by-blockheight
      // and lock-by-blocktime, distinguished by whether
      // nLockTime < LOCKTIME_THRESHOLD.
      //
      // We want to compare apples to apples, so fail the script
      // unless the type of nLockTime being tested is the same as
      // the nLockTime in the transaction.
      if (!(
          (txTo->nLockTime <  LOCKTIME_THRESHOLD && nLockTime <  LOCKTIME_THRESHOLD) ||
          (txTo->nLockTime >= LOCKTIME_THRESHOLD && nLockTime >= LOCKTIME_THRESHOLD)
      ))
          return false;
  
      // Now that we know we're comparing apples-to-apples, the
      // comparison is a simple numeric one.
      if (nLockTime > (int64_t)txTo->nLockTime)
          return false;
  
      // Finally the nLockTime feature can be disabled and thus
      // CHECKLOCKTIMEVERIFY bypassed if every txin has been
      // finalized by setting nSequence to maxint. The
      // transaction would be allowed into the blockchain, making
      // the opcode ineffective.
      //
      // Testing if this vin is not final is sufficient to
      // prevent this condition. Alternatively we could test all
      // inputs, but testing just this input minimizes the data
      // required to prove correct CHECKLOCKTIMEVERIFY execution.
      if (CTxIn::SEQUENCE_FINAL == txTo->vin[nIn].nSequence)
          return false;
  
      return true;
  }
  
  bool TransactionSignatureChecker::CheckSequence(const CScriptNum& nSequence) const
  {
      // Relative lock times are supported by comparing the passed
      // in operand to the sequence number of the input.
      const int64_t txToSequence = (int64_t)txTo->vin[nIn].nSequence;
  
      // Fail if the transaction's version number is not set high
      // enough to trigger BIP 68 rules.
      if (static_cast<uint32_t>(txTo->nVersion) < 2)
          return false;
  
      // Sequence numbers with their most significant bit set are not
      // consensus constrained. Testing that the transaction's sequence
      // number do not have this bit set prevents using this property
      // to get around a CHECKSEQUENCEVERIFY check.
      if (txToSequence & CTxIn::SEQUENCE_LOCKTIME_DISABLE_FLAG)
          return false;
  
      // Mask off any bits that do not have consensus-enforced meaning
      // before doing the integer comparisons
      const uint32_t nLockTimeMask = CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG | CTxIn::SEQUENCE_LOCKTIME_MASK;
      const int64_t txToSequenceMasked = txToSequence & nLockTimeMask;
      const CScriptNum nSequenceMasked = nSequence & nLockTimeMask;
  
      // There are two kinds of nSequence: lock-by-blockheight
      // and lock-by-blocktime, distinguished by whether
      // nSequenceMasked < CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG.
      //
      // We want to compare apples to apples, so fail the script
      // unless the type of nSequenceMasked being tested is the same as
      // the nSequenceMasked in the transaction.
      if (!(
          (txToSequenceMasked <  CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG && nSequenceMasked <  CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG) ||
          (txToSequenceMasked >= CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG && nSequenceMasked >= CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG)
      )) {
          return false;
      }
  
      // Now that we know we're comparing apples-to-apples, the
      // comparison is a simple numeric one.
      if (nSequenceMasked > txToSequenceMasked)
          return false;
  
      return true;
  }
  
  static bool VerifyWitnessProgram(const CScriptWitness& witness, int witversion, const std::vector<unsigned char>& program, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror)
  {
      std::vector<std::vector<unsigned char> > stack;
      CScript scriptPubKey;
  
      if (witversion == 0) {
          if (program.size() == 32) {
              // Version 0 segregated witness program: SHA256(CScript) inside the program, CScript + inputs in witness
              if (witness.stack.size() == 0) {
                  return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_WITNESS_EMPTY);
              }
              scriptPubKey = CScript(witness.stack.back().begin(), witness.stack.back().end());
              stack = std::vector<std::vector<unsigned char> >(witness.stack.begin(), witness.stack.end() - 1);
              uint256 hashScriptPubKey;
              CSHA256().Write(&scriptPubKey[0], scriptPubKey.size()).Finalize(hashScriptPubKey.begin());
              if (memcmp(hashScriptPubKey.begin(), program.data(), 32)) {
                  return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH);
              }
          } else if (program.size() == 20) {
              // Special case for pay-to-pubkeyhash; signature + pubkey in witness
              if (witness.stack.size() != 2) {
                  return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); // 2 items in witness
              }
              scriptPubKey << OP_DUP << OP_HASH160 << program << OP_EQUALVERIFY << OP_CHECKSIG;
              stack = witness.stack;
          } else {
              return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_WRONG_LENGTH);
          }
      } else if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM) {
          return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM);
      } else {
          // Higher version witness scripts return true for future softfork compatibility
          return set_success(serror);
      }
  
      // Disallow stack item size > MAX_SCRIPT_ELEMENT_SIZE in witness stack
      for (unsigned int i = 0; i < stack.size(); i++) {
          if (stack.at(i).size() > MAX_SCRIPT_ELEMENT_SIZE)
              return set_error(serror, SCRIPT_ERR_PUSH_SIZE);
      }
  
      if (!EvalScript(stack, scriptPubKey, flags, checker, SIGVERSION_WITNESS_V0, serror)) {
          return false;
      }
  
      // Scripts inside witness implicitly require cleanstack behaviour
      if (stack.size() != 1)
          return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
      if (!CastToBool(stack.back()))
          return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
      return true;
  }
  
  bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CScriptWitness* witness, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror)
  {
      static const CScriptWitness emptyWitness;
      if (witness == nullptr) {
          witness = &emptyWitness;
      }
      bool hadWitness = false;
  
      set_error(serror, SCRIPT_ERR_UNKNOWN_ERROR);
  
      if ((flags & SCRIPT_VERIFY_SIGPUSHONLY) != 0 && !scriptSig.IsPushOnly()) {
          return set_error(serror, SCRIPT_ERR_SIG_PUSHONLY);
      }
  
      std::vector<std::vector<unsigned char> > stack, stackCopy;
      if (!EvalScript(stack, scriptSig, flags, checker, SIGVERSION_BASE, serror))
          // serror is set
          return false;
      if (flags & SCRIPT_VERIFY_P2SH)
          stackCopy = stack;
      if (!EvalScript(stack, scriptPubKey, flags, checker, SIGVERSION_BASE, serror))
          // serror is set
          return false;
      if (stack.empty())
          return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
      if (CastToBool(stack.back()) == false)
          return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
  
      // Bare witness programs
      int witnessversion;
      std::vector<unsigned char> witnessprogram;
      if (flags & SCRIPT_VERIFY_WITNESS) {
          if (scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
              hadWitness = true;
              if (scriptSig.size() != 0) {
                  // The scriptSig must be _exactly_ CScript(), otherwise we reintroduce malleability.
                  return set_error(serror, SCRIPT_ERR_WITNESS_MALLEATED);
              }
              if (!VerifyWitnessProgram(*witness, witnessversion, witnessprogram, flags, checker, serror)) {
                  return false;
              }
              // Bypass the cleanstack check at the end. The actual stack is obviously not clean
              // for witness programs.
              stack.resize(1);
          }
      }
  
      // Additional validation for spend-to-script-hash transactions:
      if ((flags & SCRIPT_VERIFY_P2SH) && scriptPubKey.IsPayToScriptHash())
      {
          // scriptSig must be literals-only or validation fails
          if (!scriptSig.IsPushOnly())
              return set_error(serror, SCRIPT_ERR_SIG_PUSHONLY);
  
          // Restore stack.
          swap(stack, stackCopy);
  
          // stack cannot be empty here, because if it was the
          // P2SH  HASH <> EQUAL  scriptPubKey would be evaluated with
          // an empty stack and the EvalScript above would return false.
          assert(!stack.empty());
  
          const valtype& pubKeySerialized = stack.back();
          CScript pubKey2(pubKeySerialized.begin(), pubKeySerialized.end());
          popstack(stack);
  
          if (!EvalScript(stack, pubKey2, flags, checker, SIGVERSION_BASE, serror))
              // serror is set
              return false;
          if (stack.empty())
              return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
          if (!CastToBool(stack.back()))
              return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
  
          // P2SH witness program
          if (flags & SCRIPT_VERIFY_WITNESS) {
              if (pubKey2.IsWitnessProgram(witnessversion, witnessprogram)) {
                  hadWitness = true;
                  if (scriptSig != CScript() << std::vector<unsigned char>(pubKey2.begin(), pubKey2.end())) {
                      // The scriptSig must be _exactly_ a single push of the redeemScript. Otherwise we
                      // reintroduce malleability.
                      return set_error(serror, SCRIPT_ERR_WITNESS_MALLEATED_P2SH);
                  }
                  if (!VerifyWitnessProgram(*witness, witnessversion, witnessprogram, flags, checker, serror)) {
                      return false;
                  }
                  // Bypass the cleanstack check at the end. The actual stack is obviously not clean
                  // for witness programs.
                  stack.resize(1);
              }
          }
      }
  
      // The CLEANSTACK check is only performed after potential P2SH evaluation,
      // as the non-P2SH evaluation of a P2SH script will obviously not result in
      // a clean stack (the P2SH inputs remain). The same holds for witness evaluation.
      if ((flags & SCRIPT_VERIFY_CLEANSTACK) != 0) {
          // Disallow CLEANSTACK without P2SH, as otherwise a switch CLEANSTACK->P2SH+CLEANSTACK
          // would be possible, which is not a softfork (and P2SH should be one).
          assert((flags & SCRIPT_VERIFY_P2SH) != 0);
          assert((flags & SCRIPT_VERIFY_WITNESS) != 0);
          if (stack.size() != 1) {
              return set_error(serror, SCRIPT_ERR_CLEANSTACK);
          }
      }
  
      if (flags & SCRIPT_VERIFY_WITNESS) {
          // We can't check for correct unexpected witness data if P2SH was off, so require
          // that WITNESS implies P2SH. Otherwise, going from WITNESS->P2SH+WITNESS would be
          // possible, which is not a softfork.
          assert((flags & SCRIPT_VERIFY_P2SH) != 0);
          if (!hadWitness && !witness->IsNull()) {
              return set_error(serror, SCRIPT_ERR_WITNESS_UNEXPECTED);
          }
      }
  
      return set_success(serror);
  }
  
  size_t static WitnessSigOps(int witversion, const std::vector<unsigned char>& witprogram, const CScriptWitness& witness, int flags)
  {
      if (witversion == 0) {
          if (witprogram.size() == 20)
              return 1;
  
          if (witprogram.size() == 32 && witness.stack.size() > 0) {
              CScript subscript(witness.stack.back().begin(), witness.stack.back().end());
              return subscript.GetSigOpCount(true);
          }
      }
  
      // Future flags may be implemented here.
      return 0;
  }
  
  size_t CountWitnessSigOps(const CScript& scriptSig, const CScript& scriptPubKey, const CScriptWitness* witness, unsigned int flags)
  {
      static const CScriptWitness witnessEmpty;
  
      if ((flags & SCRIPT_VERIFY_WITNESS) == 0) {
          return 0;
      }
      assert((flags & SCRIPT_VERIFY_P2SH) != 0);
  
      int witnessversion;
      std::vector<unsigned char> witnessprogram;
      if (scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
          return WitnessSigOps(witnessversion, witnessprogram, witness ? *witness : witnessEmpty, flags);
      }
  
      if (scriptPubKey.IsPayToScriptHash() && scriptSig.IsPushOnly()) {
          CScript::const_iterator pc = scriptSig.begin();
          std::vector<unsigned char> data;
          while (pc < scriptSig.end()) {
              opcodetype opcode;
              scriptSig.GetOp(pc, opcode, data);
          }
          CScript subscript(data.begin(), data.end());
          if (subscript.IsWitnessProgram(witnessversion, witnessprogram)) {
              return WitnessSigOps(witnessversion, witnessprogram, witness ? *witness : witnessEmpty, flags);
          }
      }
  
      return 0;
  }
  