Question

I want to have a fast log1p function for Java. Java has Math.log1p, but it is apparently too slow for my needs.

I have found this code for log1p here:

http://golang.org/src/pkg/math/log1p.go

for the GO language.

Is it the same like the one in Java, or is it a faster one? (assuming I translate it to java).
Anyone is aware of some other fast implementation of log1p?

Thanks.

Answer 1

since log1p(x) = Math.log(x+1), finding a natural log fast algorithm is sufficient for what you need.

Fast Natural Logarithm in Java

I have found the following approximation here, and there is not much
information about it except that it is called “Borchardt’s Algorithm”
and it is from the book “Dead Reconing: Calculating without
instruments”. The approximation is not very good (some might say very
bad…), it gets worse the larger the values are. But the approximation
is also a monotonic, slowly increasing function, which is good enough
for my use case.

public static double log(double x) {
return 6 * (x – 1) / (x + 1 + 4 * (Math.sqrt(x))); }

This approximation is 11.7 times faster than Math.log().

See this site. Also, a performance comparison for math libraries in java.

But probably what you need is to link to c++ compiled stuff, detailed here.