topic Re:ippsThreshold_LTAbsVal_64f weird behaviour in Intel® Integrated Performance Primitives

ippsThreshold_LTAbsVal_64f weird behaviour

agildr — Thu, 30 Sep 2021 13:45:44 GMT

Hi,

I'm trying to use ippsThreshold_LTAbsVal_64f to replace small numbers by zero.

According to the documentation a call like ippsThreshold_LTAbsVal_64f(xPtr, resultPtr, length, eps, 0.0) should replace all numbers in x that are in magnitude smaller than eps by zero.

To quote the docs, the logic is:

if( ABS(x[i]) < level ) y[i] = value; else y[i] = x[i];

I have written the following C# program. I hope it is OK to post C# code, I also had no problems with any other IPP function from C# so far, only this one.

static class IPP { [SuppressUnmanagedCodeSecurity, DllImport("libippcore.so", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)] public static extern int ippInit(); [SuppressUnmanagedCodeSecurity, DllImport("libipps.so", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)] public static extern unsafe int ippsThreshold_LTAbsVal_64f(double* pSrc, double* pDst, int len, double level, double value); } static class Program { static unsafe void IppSanityCheck(int index1, int index2) { const int length = 10000; var array = new double[length]; var result = new double[length]; const double eps = 1e-6; // setting some indices to values |.| > eps array[index1] = 100.0; array[index2] = -95.0; for (var i = 0; i < length; i++) { if (array[i] != 0.0) { Console.WriteLine("Input index {0} contains non-zero value: {1}", i, array[i]); } } fixed (double* arrayPtr = array, resultPtr = result) { var statusCode = IPP.ippsThreshold_LTAbsVal_64f(arrayPtr, resultPtr, length, eps, 0); Console.WriteLine("{0} exited with {1}", nameof(IPP.ippsThreshold_LTAbsVal_64f), statusCode); } // expect same vector as result for (var i = 0; i < length; i++) { if (Math.Abs(array[i] - result[i]) > 1e-16) { Console.WriteLine("Result index {0} differs from input: {1} vs. {2}", i, array[i], result[i]); } } } static void Main(string[] args) { if (IPP.ippInit() == 0) { IppSanityCheck(534, 1096); IppSanityCheck(1,2); } return; } }

This is the output:

Input index 534 contains non-zero value: 100 Input index 1096 contains non-zero value: -95 ippsThreshold_LTAbsVal_64f exited with 0 Result index 534 differs from input: 100 vs. 0 Result index 1096 differs from input: -95 vs. 0 Input index 1 contains non-zero value: 100 Input index 2 contains non-zero value: -95 ippsThreshold_LTAbsVal_64f exited with 0 The program 'dotnet' has exited with code 0 (0x0).

As you can see when calling it with the first input (all zero except for indices 534 and 1096) the non-zero indices get replaced by zero (wrong). When calling it with the second input (now indices 1 and 2) they are not replaced (correct).

Running on Docker/WSL2, x64, Debian 10, .NET 5, IPP is from the Intel APT repo:

# uname -a Linux 2d1918de08d8 5.10.16.3-microsoft-standard-WSL2 #1 SMP Fri Apr 2 22:23:49 UTC 2021 x86_64 GNU/Linux # dpkg -l | grep intel ii intel-oneapi-runtime-ipp 2021.3.0-333 amd64 Intel® Integrated Performance Primitives runtime ii intel-oneapi-runtime-ipp-common 2021.3.0-333 all Intel® Integrated Performance Primitives runtime common ii intel-oneapi-runtime-openmp 2021.3.0-3350 amd64 Intel® OpenMP* Runtime Library runtime ii intel-oneapi-runtime-openmp-common 2021.3.0-3350 all l_openmp.runtime.description> ii intel-oneapi-runtime-tbb 2021.3.0-511 amd64 Intel® oneAPI Threading Building Blocks runtime ii intel-oneapi-runtime-tbb-common 2021.3.0-511 all Intel® oneAPI Threading Building Blocks runtime common #

But I have tried on Windows as well and the behavior is the same.

Best,

agildr

Re:ippsThreshold_LTAbsVal_64f weird behaviour

ShanmukhS_Intel — Fri, 01 Oct 2021 10:49:10 GMT

Hi,

Thanks for reaching out to us.

We have tried compiling and executing the shared code.

>>if( ABS(x[i]) < level ) y[i] = value;

else y[i] = x[i];

As per the absolute threshold formula, among the indices shared by you,

Considering 1st case 100

Absolute of 100 which is 100 and greater than 1e-6. Hence the threshold doesn't get affected.

Considering 2nd case -95

Absolute of -95 which is 95 and greater than 1e-6. Hence the threshold doesn't get affected.

Kindly let us know if any difference in understanding.

Best Regards,

Shanmukh.SS

Re: ippsThreshold_LTAbsVal_64f weird behaviour

agildr — Mon, 04 Oct 2021 08:12:54 GMT

Hi Shanmukh.SS,

Yes, with the values supplied (0, -95, 100) the result should be the same as the input, since nothing ever is under the threshold (in magnitude), and zero already is equal to zero.

This works with the vector [0,100,-95,0,...,0] (length 10000). However, in the case where I put the 100 at index 534 and -95 at index 1096 I get a different vector (all zeroes) back.

Best,

agildr

Re:ippsThreshold_LTAbsVal_64f weird behaviour

ShanmukhS_Intel — Wed, 06 Oct 2021 09:08:12 GMT

Hi,

Thank you for sharing the details. The issue is reproducible with indices 534 and 1096 for which the results should have been 100 and -95. Instead, it is returning 0.

We are looking into your issue. We will get back to you soon.

Best Regards,

Shanmukh.SS

Re: ippsThreshold_LTAbsVal_64f weird behaviour

Andrey_B_Intel — Thu, 07 Oct 2021 15:55:50 GMT

Hi Agildr.

I confirm this issue with ippsThreshold_LTAbsVal_64f.

Fix will be available in one of next IPP releases.

Thanks.

Andrey.

Re: ippsThreshold_LTAbsVal_64f weird behaviour

agildr — Tue, 12 Oct 2021 17:23:34 GMT

Hi Andrey,

Thanks for the reply.

Can you maybe offer any insights on which constellations trigger this bug?

I'm asking because I have another test case, posting it below.

const int len = 10000; var x = new double[len]; var y = new double[len]; x[1] = 100; x[2] = -95; unsafe { fixed (double* xPtr = x, yPtr = y) { IPP.ippsThreshold_LTAbsVal_64f(xPtr, yPtr, len, 0.01, 1000); } }

First elements of y:

1000 100 -95 1000 1000 0 0 1000 1000 0 0 1000 1000 0 0 1000

Best,

Luca