public static bool CompareAlmostEqual(float x, float y, float epsilon) {
    // Based upon implementation:
    // http://floating-point-gui.de/errors/comparison/

    if (x == y)
        return true;

    float absX = Math.Abs(x);
    float absY = Math.Abs(y);
    float diff = Math.Abs(x - y);

    if (x * y == 0)
        return diff < (epsilon * epsilon);
    else if (absX + absY == diff) // [1]
        return diff < epsilon;
    else
        return diff / (absX + absY) < epsilon;
}

// Without [1] the following test fail:
[TestCase( 0.0001f, -0.0001f, 0.000001f )]
[TestCase( 0.000000000001f, -0.000000000001f, 0.000001f )]

// With [1] the following test still fails (as expected):
[TestCase( 0.0001f, -0.0001f, 0.000001f )]
// But this one passes:
[TestCase( 0.000000000001f, -0.000000000001f, 0.000001f )]


// The following tests are still failing:
Assert.False(AlmostEqual(0.000000001f, -float.Epsilon));
  Failed: InvalidNumbersVeryCloseToZero(1E-09, -1.401298E-45)
Assert.False(AlmostEqual(0.000000001f, float.Epsilon));
  Failed: InvalidNumbersVeryCloseToZero(1E-09, 1.401298E-45)
Assert.False(AlmostEqual(float.Epsilon, 0.000000001f));
  Failed: InvalidNumbersVeryCloseToZero(1.401298E-45, 1E-09)
Assert.False(AlmostEqual(-float.Epsilon, 0.000000001f));
  Failed: InvalidNumbersVeryCloseToZero(-1.401298E-45, 1E-09)

Assert.False(AlmostEqual(1e25f * float.Epsilon, -1e25f * float.Epsilon, 1e-12f));
  Failed: InvalidNumbersVeryCloseToZeroCustomDelta(1.401298E-20, -1.401298E-20, 1E-12)