On Fri, Feb 07, 2003 at 02:16:08 +0100, David Olofson wrote: > On Friday 07 February 2003 10.55, Steve Harris wrote: > > On Thu, Feb 06, 2003 at 11:13:45 +0100, David Olofson wrote: > > > On Thursday 06 February 2003 16.28, Steve Harris wrote: > > > [...] > > > > > > > #define FLUSH_TO_ZERO(fv) (((*(unsigned > > > > int*)&(fv))&0x7f800000)==0)?0.0f:(fv) I think it came from the > > > > music-dsp list. > > > > > > There's a conditional in there, though. > > > > Yes, but its not in a float context so it wont get > > denormallised(?). > > Well, casting to int avoids getting the denormal into the FPU. This is > probably the only safe way to deal with a denormal without forcing > the FPU to burn cycles evaluating it. I don't see how this has > anything to do with the conditional, though. It's a potential > misprediction + pipeline flush regardless of whether the controlling > input comes from the FPU or the ALU.
Its not a true cast, and the branch is cheaper than the denormal. Much cheaper. - Steve
