text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2020 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_TEST_SCRIPTNUM10_H
  #define BITCOIN_TEST_SCRIPTNUM10_H
  
  #include <assert.h>
  #include <limits>
  #include <stdexcept>
  #include <stdint.h>
  #include <string>
  #include <vector>
  
  class scriptnum10_error : public std::runtime_error
  {
  public:
      explicit scriptnum10_error(const std::string& str) : std::runtime_error(str) {}
  };
  
  class CScriptNum10
  {
  /**
   * The ScriptNum implementation from Bitcoin Core 0.10.0, for cross-comparison.
   */
  public:
  
      explicit CScriptNum10(const int64_t& n)
      {
          m_value = n;
      }
  
      static const size_t nDefaultMaxNumSize = 4;
  
      explicit CScriptNum10(const std::vector<unsigned char>& vch, bool fRequireMinimal,
                          const size_t nMaxNumSize = nDefaultMaxNumSize)
      {
          if (vch.size() > nMaxNumSize) {
              throw scriptnum10_error("script number overflow");
          }
          if (fRequireMinimal && vch.size() > 0) {
              // Check that the number is encoded with the minimum possible
              // number of bytes.
              //
              // If the most-significant-byte - excluding the sign bit - is zero
              // then we're not minimal. Note how this test also rejects the
              // negative-zero encoding, 0x80.
              if ((vch.back() & 0x7f) == 0) {
                  // One exception: if there's more than one byte and the most
                  // significant bit of the second-most-significant-byte is set
                  // it would conflict with the sign bit. An example of this case
                  // is +-255, which encode to 0xff00 and 0xff80 respectively.
                  // (big-endian).
                  if (vch.size() <= 1 || (vch[vch.size() - 2] & 0x80) == 0) {
                      throw scriptnum10_error("non-minimally encoded script number");
                  }
              }
          }
          m_value = set_vch(vch);
      }
  
      inline bool operator==(const int64_t& rhs) const    { return m_value == rhs; }
      inline bool operator!=(const int64_t& rhs) const    { return m_value != rhs; }
      inline bool operator<=(const int64_t& rhs) const    { return m_value <= rhs; }
      inline bool operator< (const int64_t& rhs) const    { return m_value <  rhs; }
      inline bool operator>=(const int64_t& rhs) const    { return m_value >= rhs; }
      inline bool operator> (const int64_t& rhs) const    { return m_value >  rhs; }
  
      inline bool operator==(const CScriptNum10& rhs) const { return operator==(rhs.m_value); }
      inline bool operator!=(const CScriptNum10& rhs) const { return operator!=(rhs.m_value); }
      inline bool operator<=(const CScriptNum10& rhs) const { return operator<=(rhs.m_value); }
      inline bool operator< (const CScriptNum10& rhs) const { return operator< (rhs.m_value); }
      inline bool operator>=(const CScriptNum10& rhs) const { return operator>=(rhs.m_value); }
      inline bool operator> (const CScriptNum10& rhs) const { return operator> (rhs.m_value); }
  
      inline CScriptNum10 operator+(   const int64_t& rhs)    const { return CScriptNum10(m_value + rhs);}
      inline CScriptNum10 operator-(   const int64_t& rhs)    const { return CScriptNum10(m_value - rhs);}
      inline CScriptNum10 operator+(   const CScriptNum10& rhs) const { return operator+(rhs.m_value);   }
      inline CScriptNum10 operator-(   const CScriptNum10& rhs) const { return operator-(rhs.m_value);   }
  
      inline CScriptNum10& operator+=( const CScriptNum10& rhs)       { return operator+=(rhs.m_value);  }
      inline CScriptNum10& operator-=( const CScriptNum10& rhs)       { return operator-=(rhs.m_value);  }
  
      inline CScriptNum10 operator-()                         const
      {
          assert(m_value != std::numeric_limits<int64_t>::min());
          return CScriptNum10(-m_value);
      }
  
      inline CScriptNum10& operator=( const int64_t& rhs)
      {
          m_value = rhs;
          return *this;
      }
  
      inline CScriptNum10& operator+=( const int64_t& rhs)
      {
          assert(rhs == 0 || (rhs > 0 && m_value <= std::numeric_limits<int64_t>::max() - rhs) ||
                             (rhs < 0 && m_value >= std::numeric_limits<int64_t>::min() - rhs));
          m_value += rhs;
          return *this;
      }
  
      inline CScriptNum10& operator-=( const int64_t& rhs)
      {
          assert(rhs == 0 || (rhs > 0 && m_value >= std::numeric_limits<int64_t>::min() + rhs) ||
                             (rhs < 0 && m_value <= std::numeric_limits<int64_t>::max() + rhs));
          m_value -= rhs;
          return *this;
      }
  
      int getint() const
      {
          if (m_value > std::numeric_limits<int>::max())
              return std::numeric_limits<int>::max();
          else if (m_value < std::numeric_limits<int>::min())
              return std::numeric_limits<int>::min();
          return m_value;
      }
  
      std::vector<unsigned char> getvch() const
      {
          return serialize(m_value);
      }
  
      static std::vector<unsigned char> serialize(const int64_t& value)
      {
          if(value == 0)
              return std::vector<unsigned char>();
  
          std::vector<unsigned char> result;
          const bool neg = value < 0;
          uint64_t absvalue = neg ? -value : value;
  
          while(absvalue)
          {
              result.push_back(absvalue & 0xff);
              absvalue >>= 8;
          }
  
  //    - If the most significant byte is >= 0x80 and the value is positive, push a
  //    new zero-byte to make the significant byte < 0x80 again.
  
  //    - If the most significant byte is >= 0x80 and the value is negative, push a
  //    new 0x80 byte that will be popped off when converting to an integral.
  
  //    - If the most significant byte is < 0x80 and the value is negative, add
  //    0x80 to it, since it will be subtracted and interpreted as a negative when
  //    converting to an integral.
  
          if (result.back() & 0x80)
              result.push_back(neg ? 0x80 : 0);
          else if (neg)
              result.back() |= 0x80;
  
          return result;
      }
  
  private:
      static int64_t set_vch(const std::vector<unsigned char>& vch)
      {
        if (vch.empty())
            return 0;
  
        int64_t result = 0;
        for (size_t i = 0; i != vch.size(); ++i)
            result |= static_cast<int64_t>(vch[i]) << 8*i;
  
        // If the input vector's most significant byte is 0x80, remove it from
        // the result's msb and return a negative.
        if (vch.back() & 0x80)
            return -((int64_t)(result & ~(0x80ULL << (8 * (vch.size() - 1)))));
  
        return result;
      }
  
      int64_t m_value;
  };
  
  
  #endif // BITCOIN_TEST_BIGNUM_H
  