topic thanks Zygfryd. We will in Intel® Integrated Performance Primitives

Division by infinity problem

krzysztofpiotrowski — Fri, 14 Jul 2017 11:59:04 GMT

Hello,

I am using IPP 2017 update 3 as single-threaded static library on Visual Studio 2015. My runtime environments are:

Intel® Core™ i7-3770 CPU @ 3.40GHz on Windows 7,
Intel® Xeon® CPU E5-1650 v4 @ 3.60GHz on Windows 10.

I found a problem with division of finite number by infinity (like 1/inf) with the following functions:

ippsDiv_32f,
ippsDiv_32f_I,
ippiDiv_32f_C1R,
ippiDiv_32f_C1IR

As the result of operation I receive NaN instead of 0.

I checked that the problem does not exist on Intel® Core™2 Quad Processor Q8400 CPU.

I also confirmed that the problem does not exist on i7 and Xeon CPUs when I enable only these features which are supported by Core 2 Quad:

ippCPUID_MMX,
ippCPUID_SSE,
ippCPUID_SSE2,
ippCPUID_SSE3,
ippCPUID_SSSE3,
ippCPUID_SSE41.

When I enable ippCPUID_SSE42 feature, the problem can be spot again.

I checked also ippsDiv_64f and it seems the it works properly.

Please also find the attached full table of results for different set of cpuFeatures and particular division arguments.

HI, thanks for your report.

Chao_Y_Intel — Fri, 04 Aug 2017 15:52:43 GMT

HI, thanks for your report. We rooted the problem, and will fix it in our future product release ( likely it will in IPP 2018 update 1 release).

Regards,
Chao

I'd like to confirm that the

krzysztofpiotrowski — Wed, 22 Nov 2017 06:15:14 GMT

I'd like to confirm that the problem has been fixed in IPP 2018 Update 1. Thank you very much for your support.

Dear Chao

Wieszok__Zygfryd — Wed, 13 Dec 2017 10:50:57 GMT

Dear Chao

I have verified the results of division operation in Ipp 2018 Update 1 and there are still some issues with infinity arithmetics. The division operation for 1 / inf and 0 / inf works correctly but there are still some issues for inf / constant.

For example for the given code:

#include <ipp.h>
#include <limits>
#include <iostream>

int main()
{
	ippInit();

	const IppLibraryVersion *lib;
	lib = ippsGetLibVersion();
	printf("CPU       : %s\n", lib->targetCpu);
	printf("Name      : %s\n", lib->Name);
	printf("Version   : %s\n", lib->Version);
	printf("Build date: %s\n", lib->BuildDate);


	auto inf = std::numeric_limits<float>::infinity();

	int step1, step2, step3;
	
	float* a = ippiMalloc_32f_C1(1, 1, &step1);
	float* b = ippiMalloc_32f_C1(1, 1, &step2);
	float* c = ippiMalloc_32f_C1(1, 1, &step3);

	a[0] = inf;
	b[0] = 10;
	for (size_t i = 0; i < 9; i++)
	{
		b[0] += 0.1;
		ippiDiv_32f_C1R(b, step1, a, step2, c, step2, { 1,1 });
		std::cout <<  a[0] << " / " << b[0] <<" =  Without IPP: " << a[0] / b[0] << " Ipp: " << c[0] << std::endl;
	}
}

the results are as follow:

as you can see the results are not stable.

Regards
Zygfryd

thanks Zygfryd. We will

Chao_Y_Intel — Thu, 14 Dec 2017 03:54:05 GMT

thanks Zygfryd. We will check this.

regards,
Chao