code: func calcMemSize64(off, l *big.Int) (uint64, bool) {
  	if !l.IsUint64() {
  		return 0, true
  	}
  	return calcMemSize64WithUint(off, l.Uint64())
  }
docs: // calcMemSize64 calculates the required memory size, and returns
  // the size and whether the result overflowed uint64