Armadillo, Intel icpx and NaN's

[Daniel_H]

Hi,

When running the small piece of code given below, NaN's are reported as 0 when compiling with icpx in any optimization other than -O0.

Any other compiler (eg: g++, icpc, clang++) works as expected printing "nan" where required.

I'm using latest icpx (2022.1.0.20220316) and armadillo (11.2.1) on linux.

Already reported it at Armadillo's developer but I've been sent here!

Any help will be really appreciated,

thank

Daniel

#define ARMA_DONT_USE_WRAPPER

// Compile with eg:  icpx -O3 -qmkl=sequential

#include <armadillo>

int main() {
  
  arma::Col<double> raw_vec;

  raw_vec.randu(4);
  raw_vec.print();
  
  std::cout << std::endl;
  
  raw_vec[0] = arma::datum::nan; 
  // Same with raw_vec[0] = std::numeric_limits<double>::quiet_NaN()
  raw_vec.print();
  
  return 0;
}

[SantoshY_Intel]

Hi,

Thank you for posting in Intel Communities.

We were able to reproduce your issue at our end. We are working on your issue and will get back to you soon.

Thanks & Regards,

Santosh

[SantoshY_Intel · Accepted solution]

Hi,

As -O2 is the default optimization level for the Intel compilers, sometimes we might get some changes in the results. To overcome this issue, we can use the "-fp-model=precise" flag which tells the compiler to strictly adhere to value-safe optimizations when implementing floating-point calculations. It disables optimizations that can change the result of floating-point calculations, which is required for strict ANSI conformance.

For more information please refer to the below link:

https://www.intel.com/content/www/us/en/develop/documentation/oneapi-dpcpp-cpp-compiler-dev-guide-and-reference/top/compiler-reference/compiler-options/floating-point-options/fp-model-fp.html

Use the below command to get the correct results:

icpx -fp-model=precise sample.cpp
./a.out

We tried at our end and we are getting the correct results. Please find the attachment(icpx_log.txt) below.

If this resolves your issue, make sure to accept this as a solution. This would help others with a similar issue. Thank you!

Best Regards,

Santosh

[Daniel_H]

Thanks Santosh,

It indeed solves the problem.

Daniel

[SantoshY_Intel]

Hi,

Thanks for accepting our solution. If you need any additional information, please post a new question as this thread will no longer be monitored by Intel.

Thanks & Regards,

Santosh