assert(ilogb(1) == 0);
assert(ilogb(3) == 1);
assert(ilogb(3.0) == 1);
assert(ilogb(100_000_000) == 26);
assert(ilogb(0) == FP_ILOGB0);
assert(ilogb(0.0) == FP_ILOGB0);
assert(ilogb(double.nan) == FP_ILOGBNAN);
assert(ilogb(double.infinity) == int.max);
Extracts the exponent of x as a signed integral value.
If x is not a special value, the result is the same as cast(int) logb(x).