public void TestReciprocal(byte color, byte alpha)
{
var rcpa = FixedMathCC8.ToReciprocalByte(FixedMathCC8.FromByte(alpha));
var final = FixedMathCC8.ToByte(FixedMathCC8.FromByte(color), rcpa);
Assert.AreEqual(color, final);
}
public void TestDivMul()
{
for (uint i = 1; i < 256; ++i)
{
var ifp = i / 255f;
for (uint j = 1; j < 256; ++j)
{
var jfp = j / 255f;
// references
var dddd = Math.Min(1, ifp / jfp);
// var mref = (uint)((ifp * jfp) * 255f);
// var dref = (uint)( dddd * 255f);
var mref = (uint)Math.Round((ifp * jfp) * 255f);
var dref = (uint)Math.Round(dddd * 255f);
Assert.Less(mref, 256);
Assert.Less(dref, 256);
TestContext.WriteLine($"{i}x{j} = {mref}");
TestContext.WriteLine($"{i}/{j} = {dref}");
// slow
var mval0 = (i * j) / 255;
var dval0 = Math.Min(255, (i * 255) / j);
Assert.Less(dval0, 256);
Assert.AreEqual(mref, mval0, 1);
Assert.AreEqual(dref, dval0, 1);
// expanded 65535
const uint U16 = 65535;
var i16 = FixedMathCC8.From255To65535(i);
var j16 = FixedMathCC8.From255To65535(j);
var mval1 = (i16 * j16) >> 16;
var dval1 = Math.Min(U16, (i16 * U16) / j16);
mval1 = FixedMathCC8.From65535To255(mval1);
dval1 = FixedMathCC8.From65535To255(dval1);
Assert.AreEqual(mref, mval1, 1);
Assert.AreEqual(dref, dval1, 1);
// reciprocal 65535
var rj15 = Math.Min(U16, (U16 * U16) / j16);
var dval2 = (i16 * rj15) >> 16;
// expanded to 4095
const uint U12 = (1 << 12) - 1;
var i12 = FixedMathCC8.FromByte(i);
var j12 = FixedMathCC8.FromByte(j);
var mval4 = (i12 * j12) >> 12;
var dval4 = Math.Min(U12, (i12 * U12) / j12);
mval4 = FixedMathCC8.ToByte(mval4);
dval4 = FixedMathCC8.ToByte(dval4);
Assert.AreEqual(mref, mval4, 1);
Assert.AreEqual(dref, dval4, 1);
// reciprocal direct to 255 (12+12+8)
var rj12 = FixedMathCC8.ToReciprocalByte(j12);
dval4 = FixedMathCC8.ToByte(i12, rj12);
Assert.AreEqual(dref, dval4, 1);
}
}
}