That would allow a double with a fractional part to return true though, which is not the intention. If you do this before the casted comparison, the cast should

That would allow a double with a fractional part to return true though, which is not the intention. If you do this before the casted comparison, the cast shouldn't produce an undefined value. I think this is a good solution without using the math library and having access to the FP status registers. Otherwise the lrint solution seems better. int fits_long(double value) { double max = (double) (1L << 52) double min = (double) -max; if( min <= value && value <= max) return( (double) (long) value == value); return( 0); }