[Tests] Fix precision constraints for FP math operations

[edanor]

Originally reported by: edanor (Bitbucket: edanor, GitHub: edanor)

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Some floating point operations rely on approximation. The problem is to test such functions against standard version with automatically generated data inputs.

What should be done is:

1. design a code pattern for calculating 'ULP distance' from the reference value,
2. create a test fail/pass threshold value expressed in this ULP distance,
3. report the ulp precision (for selected tests only) together with test result.

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• Bitbucket: https://bitbucket.org/edanor/umesimd/issue/38