[linux-audio-dev] Denormal numbers

[Jussi Laako]

On Tue, 2003-08-05 at 01:48, Simon Jenkins wrote:

> that have denormal operands, and it produces denormal results when
> calculations underflow. There is no hardware option to flush either denormal
> operands or denormal results to zero. (I think that there is such an option
> on Itanium processors though, and on some other processor families).

There is no such option for x86 family afaik. Flush-denormals-to-zero by
CPU/FPU requires use of SSE/3DNow for floating point calculations.

To get rid of at least some of the denormal performance problems one
could use "-march=pentium4 -msse2 -mfpmath=sse" on GCC or "-tpp7 -xW" on
ICC.

> The slow-down that happens with denormal calculations isn't the result
> of exception handling, its the result of the FPU hardware itself taking
> a lot longer to perform the calculations.

This performance penaly is _very_ significant on Intel CPUs and rather
low on AMD ones. However, using SSE2 for fp math on P4 fixes this.


-- 
Jussi Laako <jussi.laako at pp.inet.fi>