sunsetquest / fast-integer-log2 Goto Github PK

I was surprised to see SunsetQuest3 reported as "no errors" in the output, when it looked suspicious (floats only have a 24-bit mantissa.)

I ran some additional tests and found that there are 255 values that produce incorrect results.

In all of these these cases, the value is rounded up during the float conversion (tested in LINQPad 6, which is .NET Core).

This is the routine I used to generate my test cases:

static IEnumerable<uint> GenerateInputs32()
{
	yield return (1U);
	yield return (2U);
	yield return (3U);
	uint x = 4U;
	uint y = 6U;
	for (int i = 1; i < 31; i++)
	{
		yield return (x);
		yield return (x + 1);
		yield return (y);
		yield return ((x << 1) - 1);
		x <<= 1;
		y <<= 1;
	}
}

This tests all powers of 2, all values one less than a power of 2, all values one greater than a power of 2, and all values halfway between two powers of 2.