Hello, On Wed, 26 Apr 2023, Jakub Jelinek via Gcc-patches wrote:
> For glibc I've gathered data from: > 4) using attached ulp-tester.c (how to invoke in file comment; tested > both x86_64, ppc64, ppc64le 50M pseudo-random values in all 4 rounding > modes, plus on x86_64 float/double sin/cos using libmvec - see > attached libmvec-wrapper.c as well) That ulp-tester.c file as attached here is not testing what you think it does. (1) It doesn't compile as it doesn't #define the TESTS macro in the !LIBMVEC_TEST case, and (2) it almost never progresses 'm', the status variable used before the random numbers start, to beyond 1: you start with nextafter(0.0, 1.0), which is the smallest subnormal number (with a ERANGE error, but that's ignored), and you test for equality with THIS_MIN, the smallest normal (!) number, until you start incrementing 'm'. >From subnormal smallest to normal smallest takes 1<<mantissa-digits iterations, so will usually not be reached with reasonable arguments to ulp-tester (it will be reached for the float type with arguments beyond 1<<24, but never for float128, and also double will take too large arguments to complete in reasonable time). So the program actually only checks the first N subnormal values of the respective type. I mention this before people try to use it and are super-happy about the accuracy of their libm's cosine :-) (Just always incrementing m fixes the problem of course, but you probably intended it to do something else, maybe using __XXX_DENORM_MIN__ ?). Ciao, Michael.
