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Document some magic numbers; trailing spaces; other doc tweaks 

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1165903 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Sebastian Bazley 2011-09-06 22:17:21 +00:00
parent a1dd05b8c8
commit 0fcbaec47a
1 changed files with 26 additions and 8 deletions
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30
src/main/java/org/apache/commons/math/util/FastMath.java
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@ -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[] =
{
@ -5185,7 +5187,7 @@ public class FastMath {
};
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];
}
@ -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;