Date: Sat, 14 Jul 2001 11:28:03 -0700 From: Jim Pirzyk <Jim.Pirzyk@disney.com> To: jmcoopr@webmail.bmi.net Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: math library difference between linux emulation and native freebsd (and native linux) Message-ID: <iss.450f.3b508f31.639ad.1@mercury.fan.fa.disney.com> In-Reply-To: <200107141819.LAA06370@smtp.bmi.net>
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On Saturday, July 14, 2001, at 11:17 AM, jmcoopr@webmail.bmi.net wrote:
> In <200107141809.f6EI9M809946@snoopy.fan.fa.disney.com>, on 07/14/2001
> at 11:09 AM, Jim.Pirzyk@disney.com said:
>
>> So I have stumbled across a linux emulation bug in freebsd. Below is
>> the program that returns different results based on FreeBSD, Linux or
>> Linux emulation under FreeBSD.
>
>> Running natively under FreeBSD:
>
>> x = 53.27850000
>> exp(x) = 137581029243568449912832.00000000
>
>> Running natively under Linux:
>
>> x = 53.278500
>> exp(x) = 137581029243568449912832.000000
>
>> Running under FreeBSD in Linux emulation mode:
>
>> x = 53.27850000
>> exp(x) = 137581029243567812378624.00000000
>
>
>> #include <stdio.h>
>> #include <math.h>
>> #include <stdlib.h>
>
>> int main (int argc, char **argv) {
>> double x = 53.278500;
>
>> printf ("x = %8lf\n", x);
>> printf ("exp(x) = %8lf\n", exp(x));
>
>> exit (0);
>> }
>
>> There are only two shared libaries in common (libc and libm) and both
>> are the same on FreeBSD (in /compat/linux) and Linux.
>
>> So any ideas on where the program is going wrong?
>
>> - JimP
>
> My guess is difference between Linux emulation and "native" 's floating
> point formatting for printf. With the number of significant digits
> you're invoking, small differences in handling low order bits can be
> significant.
So I tried writing it out with write directly and did a binary compare,
they
still are different. :(
- JimP
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