> Date: Mon, 02 Jun 2014 09:34:20 +0200
> From: Benjamin Baier <program...@netzbasis.de>
>
> You might want to read up on floating point arithmetic. (rounding and
> representation)
Well, the difference between 4.994404 and 5.0 is a bit large to blame
rounding and binary representation. And other OpenBSD platforms
(amd64, sparc64, powerpc) return the expected result. So I'd say that
there is a bug in the i386-specific implementation of exp2(3).
> On 06/02/14 05:13, Daniel Dickman wrote:
> > I hit this problem while working with the numpy 1.8.1 regress suite
> > which has some tests that are currently failing.
> >
> > Here is a reduced test case of the logaddexp2 python function which
> > ends up calling exp2. Is this a bug in the openbsd exp2
> > implementation?
> >
> > ---8<---
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <math.h>
> >
> > int main(void) {
> > double x;
> > double y;
> >
> > // x = log2(5)
> > x = 2.32192809489;
> > // y = 2**(log2(5))
> > y = exp2(x);
> >
> > printf("expected: 5.0\n");
> > printf("actual: %f\n", y);
> >
> > ---8<---
> >
> > on a linux/x86_64 machine:
> >
> > # gcc -lm test.c && ./a.out
> > expected: 5.0
> > actual: 5.000000
> >
> > on an openbsd/i386 machine:
> >
> > # gcc -lm test.c && ./a.out
> > expected: 5.0
> > actual: 4.994404
> >
>
>
