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Fixed the problems the AreAlmostEqual() methods had with floating point zeros

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git-svn-id: file:///srv/devel/repo-conversion/nusu@294 d2e56fa2-650e-0410-a79f-9358c0239efd
This commit is contained in:
Markus Ewald 2014-02-24 13:31:35 +00:00
parent 0a7306bb58
commit 5fb5b1f568
2 changed files with 143 additions and 32 deletions
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107
Source/FloatHelper.Test.cs
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@ -143,25 +143,80 @@ namespace Nuclex.Support {
);
}
// http://www.altdevblogaday.com/2012/02/22/comparing-floating-point-numbers-2012-edition/
// Make both positive
// If both are negative -> fine
// If both are positive -> fine
// If different -> Measure both distances to zero in ulps and sum them
/// <summary>
/// Verifies that the negative floating point zero is within one ulp of the positive
/// floating point zero and vice versa
/// Verifies that two denormalized floats can be compared in ulps
/// </summary>
[Test]
public void NegativeZeroFloatEqualsPositiveZero() {
public void DenormalizedFloatsCanBeCompared() {
float zero = 0.0f;
float zeroPlusOneUlp = FloatHelper.ReinterpretAsFloat(
FloatHelper.ReinterpretAsInt(zero) + 1
);
float zeroMinusOneUlp = -zeroPlusOneUlp;
bool test = FloatHelper.AreAlmostEqual(zeroMinusOneUlp, zeroPlusOneUlp, 1);
// Across zero
Assert.IsFalse(FloatHelper.AreAlmostEqual(zeroMinusOneUlp, zeroPlusOneUlp, 1));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zeroPlusOneUlp, zeroMinusOneUlp, 2));
// Against zero
Assert.IsFalse(FloatHelper.AreAlmostEqual(zero, zeroPlusOneUlp, 0));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zero, zeroPlusOneUlp, 1));
Assert.IsFalse(FloatHelper.AreAlmostEqual(zero, zeroMinusOneUlp, 0));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zero, zeroMinusOneUlp, 1));
}
/// <summary>
/// Verifies that the negative floating point zero is within one ulp of the positive
/// floating point zero and vice versa
/// </summary>
[Test]
public void NegativeZeroFloatEqualsPositiveZero() {
Assert.IsTrue(
FloatHelper.AreAlmostEqual(
FloatHelper.NegativeZeroFloat, FloatHelper.PositiveZeroFloat, 0
)
);
Assert.IsTrue(
FloatHelper.AreAlmostEqual(
FloatHelper.PositiveZeroFloat, FloatHelper.NegativeZeroFloat, 0
)
);
}
/// <summary>Verifies that floats can be compared across the zero boundary</summary>
[Test]
public void FloatsCanBeComparedAcrossZeroInUlps() {
float tenUlps = float.Epsilon * 10.0f;
Assert.IsTrue(FloatHelper.AreAlmostEqual(-tenUlps, tenUlps, 20));
Assert.IsTrue(FloatHelper.AreAlmostEqual(tenUlps, -tenUlps, 20));
Assert.IsFalse(FloatHelper.AreAlmostEqual(-tenUlps, tenUlps, 19));
Assert.IsTrue(FloatHelper.AreAlmostEqual(-tenUlps, 0, 10));
Assert.IsTrue(FloatHelper.AreAlmostEqual(0, -tenUlps, 10));
Assert.IsFalse(FloatHelper.AreAlmostEqual(-tenUlps, 0, 9));
Assert.IsTrue(FloatHelper.AreAlmostEqual(0, tenUlps, 10));
Assert.IsTrue(FloatHelper.AreAlmostEqual(tenUlps, 0, 10));
Assert.IsFalse(FloatHelper.AreAlmostEqual(0, tenUlps, 9));
}
/// <summary>
/// Verifies that two denormalized doubles can be compared in ulps
/// </summary>
[Test]
public void DenormalizedDoublesCanBeCompared() {
double zero = 0.0;
double zeroPlusOneUlp = FloatHelper.ReinterpretAsDouble(
FloatHelper.ReinterpretAsLong(zero) + 1
);
double zeroMinusOneUlp = -zeroPlusOneUlp;
// Across zero
Assert.IsFalse(FloatHelper.AreAlmostEqual(zeroMinusOneUlp, zeroPlusOneUlp, 1));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zeroPlusOneUlp, zeroMinusOneUlp, 2));
// Against zero
Assert.IsFalse(FloatHelper.AreAlmostEqual(zero, zeroPlusOneUlp, 0));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zero, zeroPlusOneUlp, 1));
Assert.IsFalse(FloatHelper.AreAlmostEqual(zero, zeroMinusOneUlp, 0));
@ -174,18 +229,34 @@ namespace Nuclex.Support {
/// </summary>
[Test]
public void NegativeZeroDoubleEqualsPositiveZero() {
double zero = 0.0;
double zeroPlusOneUlp = FloatHelper.ReinterpretAsDouble(
FloatHelper.ReinterpretAsLong(zero) + 1
Assert.IsTrue(
FloatHelper.AreAlmostEqual(
FloatHelper.NegativeZeroDouble, FloatHelper.NegativeZeroDouble, 0
)
);
double zeroMinusOneUlp = -zeroPlusOneUlp;
Assert.IsTrue(
FloatHelper.AreAlmostEqual(
FloatHelper.NegativeZeroDouble, FloatHelper.NegativeZeroDouble, 0
)
);
}
bool test = FloatHelper.AreAlmostEqual(zeroMinusOneUlp, zeroPlusOneUlp, 1);
/// <summary>Verifies that doubles can be compared across the zero boundary</summary>
[Test]
public void DoublesCanBeComparedAcrossZeroInUlps() {
double tenUlps = double.Epsilon * 10.0;
Assert.IsFalse(FloatHelper.AreAlmostEqual(zero, zeroPlusOneUlp, 0));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zero, zeroPlusOneUlp, 1));
Assert.IsFalse(FloatHelper.AreAlmostEqual(zero, zeroMinusOneUlp, 0));
Assert.IsTrue(FloatHelper.AreAlmostEqual(zero, zeroMinusOneUlp, 1));
Assert.IsTrue(FloatHelper.AreAlmostEqual(-tenUlps, tenUlps, 20));
Assert.IsTrue(FloatHelper.AreAlmostEqual(tenUlps, -tenUlps, 20));
Assert.IsFalse(FloatHelper.AreAlmostEqual(-tenUlps, tenUlps, 19));
Assert.IsTrue(FloatHelper.AreAlmostEqual(-tenUlps, 0, 10));
Assert.IsTrue(FloatHelper.AreAlmostEqual(0, -tenUlps, 10));
Assert.IsFalse(FloatHelper.AreAlmostEqual(-tenUlps, 0, 9));
Assert.IsTrue(FloatHelper.AreAlmostEqual(0, tenUlps, 10));
Assert.IsTrue(FloatHelper.AreAlmostEqual(tenUlps, 0, 10));
Assert.IsFalse(FloatHelper.AreAlmostEqual(0, tenUlps, 9));
}
}