Mega Code Archive
Floating-point comparisons
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/**
* Floating-point comparisons.
* @author Ian F. Darwin, http://www.darwinsys.com/
* @version $Id: FloatCmp.java,v 1.11 2004/02/09 03:33:56 ian Exp $
*/
public class FloatCmp {
final static double EPSILON = 0.0000001;
public static void main(String[] argv) {
double da = 3 * .3333333333;
double db = 0.99999992857;
// Compare two numbers that are expected to be close.
if (da == db) {
System.out.println("Java considers " + da + "==" + db);
// else compare with our own equals method
} else if (equals(da, db, 0.0000001)) {
System.out.println("True within epsilon " + EPSILON);
} else {
System.out.println(da + " != " + db);
}
// Show that comparing two NaNs is not a good idea:
double d1 = Double.NaN;
double d2 = Double.NaN;
if (d1 == d2)
System.err.println("Comparing two NaNs incorrectly returns true.");
if (!new Double(d1).equals(new Double(d2)))
System.err.println("Double(NaN).equal(NaN) incorrectly returns false.");
}
/** Compare two doubles within a given epsilon */
public static boolean equals(double a, double b, double eps) {
if (a==b) return true;
// If the difference is less than epsilon, treat as equal.
return Math.abs(a - b) < eps;
}
/** Compare two doubles, using default epsilon */
public static boolean equals(double a, double b) {
if (a==b) return true;
// If the difference is less than epsilon, treat as equal.
return Math.abs(a - b) < EPSILON * Math.max(Math.abs(a), Math.abs(b));
}
}
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