Does numpy support this? --Guido (mobile)
On Jan 16, 2017 7:27 AM, "Stephan Houben" <stephan...@gmail.com> wrote: > Hi Steve, > > Very good! > Here is a version which also handles the nan's, infinities, > negative zeros properly. > > =============== > import math > from fractions import Fraction > > def fma2(x, y, z): > if math.isfinite(x) and math.isfinite(y) and math.isfinite(z): > result = float(Fraction(x)*Fraction(y) + Fraction(z)) > if not result and not z: > result = math.copysign(result, x*y+z) > else: > result = x * y + z > assert not math.isfinite(result) > return result > =========================== > > Stephan > > > 2017-01-16 12:04 GMT+01:00 Steven D'Aprano <st...@pearwood.info>: > >> On Mon, Jan 16, 2017 at 11:01:23AM +0100, Stephan Houben wrote: >> >> [...] >> > So the following would not be a valid FMA fallback >> > >> > double bad_fma(double x, double y, double z) { >> > return x*y + z; >> > } >> [...] >> > Upshot: if we want to provide a software fallback in the Python code, we >> > need to do something slow and complicated like musl does. >> >> I don't know about complicated. I think this is pretty simple: >> >> from fractions import Fraction >> >> def fma(x, y, z): >> # Return x*y + z with only a single rounding. >> return float(Fraction(x)*Fraction(y) + Fraction(z)) >> >> >> When speed is not the number one priority and accuracy is important, >> its hard to beat the fractions module. >> >> >> -- >> Steve >> _______________________________________________ >> Python-ideas mailing list >> Python-ideas@python.org >> https://mail.python.org/mailman/listinfo/python-ideas >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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