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copied!<p>Writing a useful general-purpose floating point <code>IsEqual</code> is very, very hard, if not outright impossible. Your current code will fail badly for <code>a==0</code>. How the method should behave for such cases is really a matter of definition, and arguably the code would best be tailored for the specific domain use case.</p> <p>For this kind of thing, you <em>really, really need</em> a good test suite. That's how I did it for <a href="http://floating-point-gui.de/errors/comparison/" rel="noreferrer">The Floating-Point Guide</a>, this is what I came up with in the end (Java code, should be easy enough to translate):</p> <pre><code>public static boolean nearlyEqual(float a, float b, float epsilon) { final float absA = Math.abs(a); final float absB = Math.abs(b); final float diff = Math.abs(a - b); if (a == b) { // shortcut, handles infinities return true; } else if (a == 0 || b == 0 || diff < Float.MIN_NORMAL) { // a or b is zero or both are extremely close to it // relative error is less meaningful here return diff < (epsilon * Float.MIN_NORMAL); } else { // use relative error return diff / (absA + absB) < epsilon; } } </code></pre> <p>You can also find <a href="http://floating-point-gui.de/errors/comparison/" rel="noreferrer">the test suite on the site</a>.</p> <p><strong>Appendix:</strong> Same code in c# for doubles (as asked in questions)</p> <pre><code>public static bool NearlyEqual(double a, double b, double epsilon) { double absA = Math.Abs(a); double absB = Math.Abs(b); double diff = Math.Abs(a - b); if (a == b) { // shortcut, handles infinities return true; } else if (a == 0 || b == 0 || diff < Double.Epsilon) { // a or b is zero or both are extremely close to it // relative error is less meaningful here return diff < epsilon; } else { // use relative error return diff / (absA + absB) < epsilon; } } </code></pre>

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