performance - Does this mean that Java Math.floor is extremely slow?

Question

I don't Java much.

I am writing some optimized math code and I was shocked by my profiler results. My code collects values, interleaves the data and then chooses the values based on that. Java runs slower than my C++ and MATLAB implementations.

I am using javac 1.7.0_05 I am using the Sun/Oracle JDK 1.7.05

There exists a floor function that performs a relevant task in the code.

1. Does anybody know of the paradigmatic way to fix this?

2. I noticed that my floor() function is defined with something called StrictMath. Is there something like -ffast-math for Java? I am expecting there must be a way to change the floor function to something more computationally reasonable without writing my own.

   public static double floor(double a) {
       return StrictMath.floor(a); // default impl. delegates to StrictMath
   }
   

Edit

So a few people suggested I try to do a cast. I tried this and there was absolutely no change in walltime.

private static int flur(float dF)
{
    return (int) dF;
}

413742 cast floor function

394675 Math.floor

These test were ran without the profiler. An effort was made to use a profiler but the runtime was drastically altered (15+ minutes so I quit).

Answer 1

You might want to give a try to FastMath.

Here is a post about the performance of Math in Java vs. Javascript. There are a few good hints about why the default math lib is slow. They are discussing other operations than floor, but I guess their findings can be generalized. I found it interesting.

EDIT

According to this bug entry, floor has been implemented a pure java code in 7(b79), 6u21(b01) resulting in better performance. The code of floor in the JDK 6 is still a bit longer than the one in FastMath, but might not be responsible for such a perf. degradation. What JDK are you using? Could you try with a more recent version?