Re: [eigen] Eigen SSE denorm modes?

[Dick Lyon <dicklyon@xxxxxxxxxx>]

Thanks, Mark, for the info on the SSE control intrinsics.  I presume these are Intel-only; does Eigen has a way to wrap them that doesnt' make the code architecture dependent?

Do these settings have persistent effect?  On the processor?  or the process?  Apple seems to say that you should restore the old control word after doing your thing, but it's not clear to me how this is scoped:  https://developer.apple.com/hardwaredrivers/ve/sse.html

Dick

On Fri, Mar 9, 2012 at 11:37 AM, Mark Borgerding <mark@xxxxxxxxxxxxxx> wrote:

On 03/08/2012 04:22 PM, Dick Lyon wrote:

Is there a way to control how Eigen deals with denormalized floats?
There are low-level SSE registers to control flushing to zero and such,
but does anyone who how to control them, or what the defaults are?

Dick

DAZ and FTZ makes a big speedup on intel machines, since handling denormals is really slow (and often only propagates rounding errors).

You can enabling these modes yourself:
   _mm_setcsr( _mm_getcsr() | (1<<15));  // FTZ
   _mm_setcsr( _mm_getcsr() | (1<<6)); // DAZ