faster Math.exp() via JNI?

Question

I need to calculate Math.exp() from java very frequently, is it possible to get a native version to run faster than java\'s Math.exp()

Answer 1

This has already been requested several times (see e.g. here). Here is an approximation to Math.exp(), copied from this blog posting:

public static double exp(double val) {
    final long tmp = (long) (1512775 * val + (1072693248 - 60801));
    return Double.longBitsToDouble(tmp << 32);
}

It is basically the same as a lookup table with 2048 entries and linear interpolation between the entries, but all this with IEEE floating point tricks. Its 5 times faster than Math.exp() on my machine, but this can vary drastically if you compile with -server.