Extract the sign of a float

Hello everybody,

I am currently developing my first CUDA application.

I have arrived at a problem at last: My kernel code performs a lot of hit checks. This is done by extracting the sign of multiple similar calculations and then performing one last, unavoidable if-check in every thread. Now the standard C way to perform sign extractions would be some kind of logical statement, implicitly causing if-statements and a LOT of branching between the threads. This is of course bad.

I did not find some kind of “sign” function in CUDA like I had initially hoped.

Currently I have 2 ideas of doing this:

[list=1]

Using atomicMax() and atomicMin() with respect to zero - does anybody know if this avoids branching ?

Writing some evil hack reading out the sign bit of the floats.

But first I wanted to post this for discussion here, as many of you seem to have great experience with CUDA.

Thansk for your time !!

Q.

CUDA supports the C99 function signbit(). The function name is overloaded, so both signbit(float) and signbit(double) can be used.