code: protected String _parseFieldName(int i)
              throws IOException, JsonParseException
      {
          /* First: let's try to see if we have a simple name: one that does
           * not cross input buffer boundary, and does not contain escape
           * sequences.
           */
          int ptr = _inputPtr;
          int hash = 0;
          final int inputLen = _inputEnd;
  
          if (ptr < inputLen) {
              do {
                  int ch = _inputBuffer[ptr];
                  if (ch == INT_APOSTROPHE) {
                      int start = _inputPtr;
                      _inputPtr = ptr+1; // to skip the quote
                      return _symbols.findSymbol(_inputBuffer, start, ptr - start, hash);
                  } else if (ch == '!') {
                      break;  // escape, can't take the fast path
                  }
                  hash = (hash * 31) + ch;
                  ++ptr;
              } while (ptr < inputLen);
          }
  
          int start = _inputPtr;
          _inputPtr = ptr;
          return _parseFieldName2(start, hash, INT_APOSTROPHE);
      }
docs: /*
  ********************************************************
  /* Internal methods, secondary parsing
  ********************************************************