Author: sebb
Date: Tue Sep 6 22:17:21 2011
New Revision: 1165903
URL: http://svn.apache.org/viewvc?rev=1165903&view=rev
Log:
Document some magic numbers; trailing spaces; other doc tweaks
Modified:
commons/proper/math/trunk/src/main/java/org/apache/commons/math/util/FastMath.java
Modified:
commons/proper/math/trunk/src/main/java/org/apache/commons/math/util/FastMath.java
URL:
http://svn.apache.org/viewvc/commons/proper/math/trunk/src/main/java/org/apache/commons/math/util/FastMath.java?rev=1165903&r1=1165902&r2=1165903&view=diff
==============================================================================
---
commons/proper/math/trunk/src/main/java/org/apache/commons/math/util/FastMath.java
(original)
+++
commons/proper/math/trunk/src/main/java/org/apache/commons/math/util/FastMath.java
Tue Sep 6 22:17:21 2011
@@ -3091,10 +3091,12 @@ public class FastMath {
Double.NaN,
};
- private static final int EXP_FRAC_TABLE_LEN = 1025;
+ private static final int TWO_POWER_10 = 1024;
+ private static final int EXP_FRAC_TABLE_LEN = TWO_POWER_10 + 1; // 0,
1/1024, ... 1024/1024
/** Exponential over the range of 0 - 1 in increments of 2^-10
* exp(x/1024) = expFracTableA[x] + expFracTableB[x].
+ * 1024 = 2^10
*/
private static final double EXP_FRAC_TABLE_A[] =
{
@@ -5181,11 +5183,11 @@ public class FastMath {
+2.0922789888E13d,
+3.55687428096E14d,
+6.402373705728E15d,
- +1.21645100408832E17d,
+ +1.21645100408832E17d,
};
- private static final int LN_MANT_LEN = 1024;
+ private static final int LN_MANT_LEN = 1024; // MAGIC NUMBER
/** Extended precision logarithm table over the range 1 - 2 in increments
of 2^-10. */
private static final double LN_MANT[][] = {
@@ -6265,7 +6267,7 @@ public class FastMath {
{-0.16624879837036133, -2.6033824355191673E-8}
};
- private static final int SINE_TABLE_LEN = 14;
+ private static final int SINE_TABLE_LEN = 14; // MAGIC NUMBER
/** Sine table (high bits). */
private static final double SINE_TABLE_A[] =
@@ -6472,7 +6474,7 @@ public class FastMath {
// Populate expFracTable
for (i = 0; i < EXP_FRAC_TABLE_A.length; i++) {
- slowexp(i/1024.0, tmp);
+ slowexp(i/1024.0, tmp); // TWO_POWER_10
EXP_FRAC_TABLE_A[i] = tmp[0];
EXP_FRAC_TABLE_B[i] = tmp[1];
}
@@ -6500,7 +6502,7 @@ public class FastMath {
printarray("COSINE_TABLE_A", SINE_TABLE_LEN, COSINE_TABLE_A);
printarray("COSINE_TABLE_B", SINE_TABLE_LEN, COSINE_TABLE_B);
printarray("TANGENT_TABLE_A", SINE_TABLE_LEN, TANGENT_TABLE_A);
- printarray("TANGENT_TABLE_B", SINE_TABLE_LEN, TANGENT_TABLE_B);
+ printarray("TANGENT_TABLE_B", SINE_TABLE_LEN, TANGENT_TABLE_B);
}
private static void printarray(String string, int expectedLen, double[][]
array2d) {
@@ -6578,6 +6580,11 @@ public class FastMath {
return x;
}
+ // cosh[z] = (exp(z) + exp(-z))/2
+
+ // for numbers with magnitude 20 or so,
+ // exp(-z) can be ignored in comparison with exp(z)
+
if (x > 20.0) {
return exp(x)/2.0;
}
@@ -6633,6 +6640,11 @@ public class FastMath {
return x;
}
+ // sinh[z] = (exp(z) - exp(-z) / 2
+
+ // for values of z larger than about 20,
+ // exp(-z) can be ignored in comparison with exp(z)
+
if (x > 20.0) {
return exp(x)/2.0;
}
@@ -6744,6 +6756,12 @@ public class FastMath {
return x;
}
+ // tanh[z] = sinh[z] / cosh[z]
+ // = (exp(z) - exp(-z)) / (exp(z) + exp(-z))
+ // = (exp(2x) - 1) / (exp(2x) + 1)
+
+ // for magnitude > 20, sinh[z] == cosh[z] in double precision
+
if (x > 20.0) {
return 1.0;
}
@@ -7283,7 +7301,7 @@ public class FastMath {
split(x, xs);
ys[0] = ys[1] = 0.0;
- for (int i = 19; i >= 0; i--) {
+ for (int i = FACT_LEN-1; i >= 0; i--) {
splitMult(xs, ys, as);
ys[0] = as[0];
ys[1] = as[1];
@@ -7329,7 +7347,7 @@ public class FastMath {
final double c = a[0] + a[1];
final double d = -(c - a[0] - a[1]);
- if (c < 8e298 && c > -8e298) {
+ if (c < 8e298 && c > -8e298) { // MAGIC NUMBER
double z = c * HEX_40000000;
a[0] = (c + z) - z;
a[1] = c - a[0] + d;
