Author: nick
Date: Sat Feb 14 22:48:29 2009
New Revision: 744579
URL: http://svn.apache.org/viewvc?rev=744579&view=rev
Log:
Implement JavaME compatible log and log10 functions
Modified:
commons/sandbox/me/trunk/src/org/apache/commons/me/math/MoreMath.java
commons/sandbox/me/trunk/test-src/org/apache/commons/me/math/TestMoreMath.java
Modified: commons/sandbox/me/trunk/src/org/apache/commons/me/math/MoreMath.java
URL:
http://svn.apache.org/viewvc/commons/sandbox/me/trunk/src/org/apache/commons/me/math/MoreMath.java?rev=744579&r1=744578&r2=744579&view=diff
==============================================================================
--- commons/sandbox/me/trunk/src/org/apache/commons/me/math/MoreMath.java
(original)
+++ commons/sandbox/me/trunk/src/org/apache/commons/me/math/MoreMath.java Sat
Feb 14 22:48:29 2009
@@ -42,6 +42,66 @@
static final double q1 = 2079.33497444540981287275926;
static final double q0 = 896.78597403663861962481162;
+ // There are all used by the log function
+ static final double log10 = 2.3025850929940459;
+ static final double logHalf = -0.69314718055994529;
+
+ /**
+ * Implement log (natural log), using Taylor
+ * series expansion
+ */
+ public static double log(double val) {
+ if(val > 0.0) {
+ // Good
+ } else if(val == 1.0) {
+ // Easy
+ return 0.0;
+ } else {
+ // Log doesn't exist for this
+ return Double.NaN;
+ }
+
+ if(val < 1.0) {
+ return _log(val);
+ } else {
+ // if x > 1, then
+ // log(x) == -log(1/x)
+ return 0 - _log( (1/val) );
+ }
+ }
+ /**
+ * Implements the base 10 logarithm
+ */
+ public static double log10(double val) {
+ return log(val) / log10;
+ }
+ /**
+ * Does the actual taylor series for 0 < x < 1
+ */
+ private static double _log(double val) {
+ double res = 0;
+ double sign = 1.0;
+ double val_m1 = val - 1.0;
+
+ // 50 times is normally ok if the value
+ // is over 0.06, otherwise up to 90
+ int steps = 50;
+ if(val < 0.06) { steps = 90; }
+
+ for(int i=1; i<=steps; i++) {
+ // Raise to the power
+ double t = val_m1;
+ for(int j=2; j<=i; j++) {
+ t = t * val_m1;
+ }
+ // Combine
+ res = res + sign*(t / ((double)i));
+ // Flip sign for next time
+ sign = sign * -1;
+ }
+ return res;
+ }
+
/**
* Implement the asin (arc-sine) function
*/
Modified:
commons/sandbox/me/trunk/test-src/org/apache/commons/me/math/TestMoreMath.java
URL:
http://svn.apache.org/viewvc/commons/sandbox/me/trunk/test-src/org/apache/commons/me/math/TestMoreMath.java?rev=744579&r1=744578&r2=744579&view=diff
==============================================================================
---
commons/sandbox/me/trunk/test-src/org/apache/commons/me/math/TestMoreMath.java
(original)
+++
commons/sandbox/me/trunk/test-src/org/apache/commons/me/math/TestMoreMath.java
Sat Feb 14 22:48:29 2009
@@ -29,6 +29,33 @@
1.1, 10, 20, 100, 1000, Math.PI, -1.4, -20
};
+ public void testLog() {
+ // Valid range
+ assertTrue( Double.isNaN( MoreMath.log( -1.0 ) ) );
+ assertEquals(0.0, MoreMath.log(1.0));
+
+ // sub 1
+ assertEquals(-2.30258509, MoreMath.log(0.1), 0.001);
+ assertEquals(-0.69314718, MoreMath.log(0.5), 0.001);
+ assertEquals(-0.10536051, MoreMath.log(0.9), 0.001);
+
+ // greater than one
+ assertEquals(0.69314718, MoreMath.log(2.0), 0.001);
+ assertEquals(1.60943791, MoreMath.log(5.0), 0.001);
+ assertEquals(2.30258509, MoreMath.log(10.0), 0.001);
+ assertEquals(2.99573227, MoreMath.log(20.0), 0.002);
+ }
+
+ public void testLog10() {
+ // Valid range
+ assertTrue( Double.isNaN( MoreMath.log( -1.0 ) ) );
+ assertEquals(0.0, MoreMath.log(1.0));
+
+ // Just a few
+ assertEquals(1.00000, MoreMath.log10(10.0), 0.001);
+ assertEquals(1.30103, MoreMath.log10(20.0), 0.001);
+ }
+
public void testASin() {
for(int i=0; i<testArcVals.length; i++) {
assertEquals(
