ippDotProd returns different results with the same arguments

[ey2]

Hi,

I call ippDotProd function with the same arguments and get different outputs from run to run.

Code example:

#include "stdafx.h"
#include <ipp.h>
#include <iostream>
#include <conio.h>
#include <vector>

void Test()
{
	static const int NTAPS = 163;
	std::vector<Ipp32fc> data(NTAPS, { 100.0f, 500.012346f });

	std::vector<Ipp32f> taps(NTAPS, 1.0f);
	
	Ipp32fc dp;
	auto status = ippsDotProd_32f32fc(taps.data(), data.data(), NTAPS, &dp);

	char str[100];
	sprintf_s(str, "dp.im = %.8f", (double)dp.im);

	std::cout << str;
}


int main()
{
	Test();
	_getch();

    return 0;
}

Output:

dp.im = 81502.06250000

or

dp.im = 81502.02343750

I use:

IPP Version 2019 Update 3

Microsoft Visual Studio Professional 2017

Windows 10

Intel Core i5-9600K CPU @ 3.70GHz 3.70 GHz

I running example in debug. Release always print

dp.im = 81502.06250000

[Abhinav_S_Intel]

Thank you for reporting the issue. We will investigate this at our end and get back to you with an update.

[Gennady_F_Intel]

Evgeny,

Please try to check if the problem would exist in the case of allocated memory aligned.  It could be easily done by using if the ippsMalloc_32fc, ippsMalloc_32f, and ippsFree  IPP functions.

Gennady

[ey2]

Gennady,

Thank you for answer. I tried to test with ippMalloc/ippFree functions. And I got a stable results from run to run. Debug always print dp.im = 81502.02343750.

I try also \Zp16 option for Visual C++ compiler and also get different results from run to run in the original test with std::vector.

Tell me please 1) why the results can differ in debug/release 2) why \Zp16 option didn't help me.