Double.MaxValue to integer is negative?

Question

Why does Double.MaxValue casted to an integral type results in a negative value, the smallest value of that type?

double maxDouble = double.MaxValue;       /         


        

Answer 1

It seems the default behaviour here is unchecked, viz that unless you explicitly specify checked, the overflow goes undetected:

 double maxDouble = double.MaxValue;       // 1.7976931348623157E+308
 long uncheckedMaxDoubleLong = (long)maxDouble;    // -9223372036854775808
 long checkedMaxDoubleLong = checked((long)maxDouble); // ** Overflow Exception

In hindsight, attempting direct conversion from double to long without validating or constraining the input first is ill advised due to 2 aspects:

• numeric range mismatches / potential for overflow
• rounding considerations

So, a better bet here may have been to use Convert.ToInt64:

 var convertedDouble = Convert.ToInt64(maxDouble);    // ** OverflowException

As this internally does the checked checking for you, and takes an opinion on rounding, viz:

 return checked((long)Math.Round(value));