topic Effect of disable FTZ mode. in Intel® Integrated Performance Primitives

Effect of disable FTZ mode.

Ha_Duy_Tuan — Mon, 13 Jul 2015 06:42:04 GMT

In this link : https://software.intel.com/en-us/forums/topic/542786

The effect describe as this sentence: "This bit doesn't affect correctness of IPP functions, in some rare cases it can affect performance only."

1. Correctness of calculation

When program disables FTZ mode, this mode doesn't affect correctness of IPP functions.
However, is correctness of other functions of Intel affected? (Ex: SIMD)

Hello,

Igor_A_Intel — Mon, 13 Jul 2015 08:07:45 GMT

Hello,

I think here are all answers: https://en.wikipedia.org/wiki/Denormal_number

regards, Igor.

Hi,

Ha_Duy_Tuan — Tue, 14 Jul 2015 11:00:21 GMT

Hi,

In above link has written:

Without gradual underflow, the subtraction a−b can underflow and produce zero even though the values are not equal. This can, in turn, lead to division by zero errors that cannot occur when gradual underflow is used.

When load DLL IPP, this error can occur. Why alway set FTZ ON when load DLL IPP?

Why priority performance instead of precision?

1) IPP == Intel Performance

Igor_A_Intel — Tue, 14 Jul 2015 11:45:17 GMT

1) IPP == Intel Performance Primitives; those who needs precision uses MatLab...

2) this is default behavior that always can be changed in your app - just change FTZ state to what you need after loading IPP, or use static linking - in this case FTZ state is not affected.

3) regarding division by zero - ippsDiv_32f/64f in case of zero divider will return correctly signed infinity without producing any exception...

regards, Igor