On Jul 31 14:40:42, mailinglists.boudew...@indes.com wrote:
> Op Tue, 30 Jul 2019 17:12:56 +0200 schreef <h...@stare.cz>:
> > This is what happens on my relatively current
> > OpenBSD bbb.stare.cz 6.5 GENERIC#0 armv7 (BeagleBone Black)
> > OpenBSD ppc.stare.cz 6.5 GENERIC#0 macppc (an old MacMini)
> >
> > #include <stdint.h>
> > #include <stdio.h>
> > #include <math.h>
> >
> > int
> > main()
> > {
> > long l;
> > double d = INT_MAX;
> >
> > l = lrint(d);
> > printf("%f is %ld\n", d, l);
> >
> > l = lround(d);
> > printf("%f is %ld\n", d, l);
> >
> > return 0;
> > }
> >
> > 2147483647.000000 is -1
> > 2147483647.000000 is -1
> >
> > That doesn't seem right: isn't INT_MAX representable as a long,
> > even on these machines where sizeof(int) == sizeof(long)?
>
> If it is less than LONG_MAX, then yes.
Less than, as in strictly less?
Why? Do you mean <= ?
> > If so, shouldn't lrint(INT_MAX) == INT_MAX = lround(INT_MAX)?
>
> If the double type provides enough mantisse (which I think it does on all
> platforms), and if I read a few C standards correctly, then yes.
>
> > On i386 (an ALIX), I see
> >
> > 2147483647.000000 is 2147483647
> > 2147483647.000000 is -1
> >
> > so lrint() returns the expected value but lround() does not.
> >
> > On the amd64s I have, I see the expected:
> > 2147483647.000000 is 2147483647
> > 2147483647.000000 is 2147483647
> >
> > Is this a bug or am I missing something obvious?
>
> I'd say it's a bug. Also with a float variable and with lrintf/lroundf the
> outcome should ideally be 2147483647.
OK, how can I help debug this?
(The code in lib/libm/src/*rint*.c seems a bit over my head.)
Jan
