text: // Copyright (c) 2014-2020 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include <base58.h>
  
  #include <hash.h>
  #include <uint256.h>
  #include <util/strencodings.h>
  #include <util/string.h>
  
  #include <assert.h>
  #include <string.h>
  
  #include <limits>
  
  /** All alphanumeric characters except for "0", "I", "O", and "l" */
  static const char* pszBase58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
  static const int8_t mapBase58[256] = {
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1, 0, 1, 2, 3, 4, 5, 6,  7, 8,-1,-1,-1,-1,-1,-1,
      -1, 9,10,11,12,13,14,15, 16,-1,17,18,19,20,21,-1,
      22,23,24,25,26,27,28,29, 30,31,32,-1,-1,-1,-1,-1,
      -1,33,34,35,36,37,38,39, 40,41,42,43,-1,44,45,46,
      47,48,49,50,51,52,53,54, 55,56,57,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
      -1,-1,-1,-1,-1,-1,-1,-1, -1,-1,-1,-1,-1,-1,-1,-1,
  };
  
  [[nodiscard]] static bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch, int max_ret_len)
  {
      // Skip leading spaces.
      while (*psz && IsSpace(*psz))
          psz++;
      // Skip and count leading '1's.
      int zeroes = 0;
      int length = 0;
      while (*psz == '1') {
          zeroes++;
          if (zeroes > max_ret_len) return false;
          psz++;
      }
      // Allocate enough space in big-endian base256 representation.
      int size = strlen(psz) * 733 /1000 + 1; // log(58) / log(256), rounded up.
      std::vector<unsigned char> b256(size);
      // Process the characters.
      static_assert(sizeof(mapBase58)/sizeof(mapBase58[0]) == 256, "mapBase58.size() should be 256"); // guarantee not out of range
      while (*psz && !IsSpace(*psz)) {
          // Decode base58 character
          int carry = mapBase58[(uint8_t)*psz];
          if (carry == -1)  // Invalid b58 character
              return false;
          int i = 0;
          for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); (carry != 0 || i < length) && (it != b256.rend()); ++it, ++i) {
              carry += 58 * (*it);
              *it = carry % 256;
              carry /= 256;
          }
          assert(carry == 0);
          length = i;
          if (length + zeroes > max_ret_len) return false;
          psz++;
      }
      // Skip trailing spaces.
      while (IsSpace(*psz))
          psz++;
      if (*psz != 0)
          return false;
      // Skip leading zeroes in b256.
      std::vector<unsigned char>::iterator it = b256.begin() + (size - length);
      // Copy result into output vector.
      vch.reserve(zeroes + (b256.end() - it));
      vch.assign(zeroes, 0x00);
      while (it != b256.end())
          vch.push_back(*(it++));
      return true;
  }
  
  std::string EncodeBase58(Span<const unsigned char> input)
  {
      // Skip & count leading zeroes.
      int zeroes = 0;
      int length = 0;
      while (input.size() > 0 && input[0] == 0) {
          input = input.subspan(1);
          zeroes++;
      }
      // Allocate enough space in big-endian base58 representation.
      int size = input.size() * 138 / 100 + 1; // log(256) / log(58), rounded up.
      std::vector<unsigned char> b58(size);
      // Process the bytes.
      while (input.size() > 0) {
          int carry = input[0];
          int i = 0;
          // Apply "b58 = b58 * 256 + ch".
          for (std::vector<unsigned char>::reverse_iterator it = b58.rbegin(); (carry != 0 || i < length) && (it != b58.rend()); it++, i++) {
              carry += 256 * (*it);
              *it = carry % 58;
              carry /= 58;
          }
  
          assert(carry == 0);
          length = i;
          input = input.subspan(1);
      }
      // Skip leading zeroes in base58 result.
      std::vector<unsigned char>::iterator it = b58.begin() + (size - length);
      while (it != b58.end() && *it == 0)
          it++;
      // Translate the result into a string.
      std::string str;
      str.reserve(zeroes + (b58.end() - it));
      str.assign(zeroes, '1');
      while (it != b58.end())
          str += pszBase58[*(it++)];
      return str;
  }
  
  bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len)
  {
      if (!ValidAsCString(str)) {
          return false;
      }
      return DecodeBase58(str.c_str(), vchRet, max_ret_len);
  }
  
  std::string EncodeBase58Check(Span<const unsigned char> input)
  {
      // add 4-byte hash check to the end
      std::vector<unsigned char> vch(input.begin(), input.end());
      uint256 hash = Hash(vch);
      vch.insert(vch.end(), (unsigned char*)&hash, (unsigned char*)&hash + 4);
      return EncodeBase58(vch);
  }
  
  [[nodiscard]] static bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int max_ret_len)
  {
      if (!DecodeBase58(psz, vchRet, max_ret_len > std::numeric_limits<int>::max() - 4 ? std::numeric_limits<int>::max() : max_ret_len + 4) ||
          (vchRet.size() < 4)) {
          vchRet.clear();
          return false;
      }
      // re-calculate the checksum, ensure it matches the included 4-byte checksum
      uint256 hash = Hash(MakeSpan(vchRet).first(vchRet.size() - 4));
      if (memcmp(&hash, &vchRet[vchRet.size() - 4], 4) != 0) {
          vchRet.clear();
          return false;
      }
      vchRet.resize(vchRet.size() - 4);
      return true;
  }
  
  bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret)
  {
      if (!ValidAsCString(str)) {
          return false;
      }
      return DecodeBase58Check(str.c_str(), vchRet, max_ret);
  }
  
  