On 2/12/14, Donovan Watteau <tso...@gmail.com> wrote:
> On Thu, 6 Feb 2014, Donovan Watteau wrote:
>> David Coppa wrote:
>> > Take the following reduced test-case, adapted from what R's code
>> > does:
>> >
>> > ---8<---
>> >
>> > #include <stdio.h>
>> > #include <stdlib.h>
>> > #include <math.h>
>> >
>> > int main(void) {
>> > double theta = 1;
>> > long double lambda, pr, pr2;
>> >
>> > lambda = (0.5*theta);
>> > pr = exp(-lambda);
>> > pr2 = expl(-lambda);
>> >
>> > printf("theta == %g, pr == %Lg, pr2 == %Lg\n", theta, pr, pr2);
>> > exit(0);
>> > }
>> >
>> > ---8<---
>> >
>> > This produces the following output on Linux (x86_64):
>> >
>> > theta == 1, pr == 0.606531, pr2 == 0.606531
>> >
>> > While on OpenBSD -current amd64:
>> >
>> > theta == 1, pr == 0.606531, pr2 == nan
>>
>> FWIW, it looks even stranger on loongson:
>>
>> $ cc -o expl expl.c -O2 -pipe -lm
>> $ ./expl
>> theta == 1, pr == -9.15569e-2474, pr2 == 6.10667e-4944
>> $ ./expl
>> theta == 1, pr == 0.606531, pr2 == 0.606531
>> $ ./expl
>> theta == 1, pr == -9.15569e-2474, pr2 == 6.10667e-4944
>>
>> $ sysctl kern.version
>> kern.version=OpenBSD 5.5-beta (GENERIC) #106: Mon Feb 3 01:47:15 MST
>> 2014
>> t...@loongson.openbsd.org:/usr/src/sys/arch/loongson/compile/GENERIC
>
> A fix has been committed, but there's still a problem on loongson with
> libm updated:
>
> $ ls -l /usr/lib/libm.so.*
> -r--r--r-- 1 root bin 926033 Feb 12 12:17 /usr/lib/libm.so.9.0
> $ cc -o expl expl.c -O2 -pipe -lm
> $ for in in 1 2 3 4 5 6 ; do ./expl ; done
> theta == 1, pr == -9.15569e-2474, pr2 == 6.10667e-4944
> theta == 1, pr == 0.606531, pr2 == 0.606531
> theta == 1, pr == 0.606531, pr2 == 0.606531
> theta == 1, pr == 0.606531, pr2 == 0.606531
> theta == 1, pr == -9.15569e-2474, pr2 == 6.10667e-4944
> theta == 1, pr == 0.606531, pr2 == 0.606531
This isn't related to exp/expl. Looks like a bug in either compiler
or libc/printf/gdtoa. I don't have the hardware so I couldn't tell
much more.
As usual, there are a few ways to fix it:
1. Debug it and provide a diff,
2. Donate hardware. Oh, BTW I have a request for loongson in
http://www.openbsd.org/want.html sitting for over a year...
