From: "Ondřej Bílka" <neleai@...>
Date: 2011-11-08T16:22:23+09:00
Subject: [ruby-core:40833] Re: [ruby-trunk - Bug #5497] Math.log10(10_000) error on HP-UX/PA

Not a bug just another example of inprecision of floats. 
On Sat, Oct 29, 2011 at 03:26:41PM +0900, The Written Word Inc wrote:
> 
> Issue #5497 has been updated by The Written Word Inc.
> 
> 
> Yui NARUSE wrote:
> > The Written Word Inc wrote:
> > >   (ia64)
> > >      p Math.log10(10_000)
> > >      4
> > 
> > Show the result of `p 4.0`.
> 
> (ia64)
>   p 4.0
>   4.0
> (pa-risc)
>   p 4.0
>   4.0
> 
> > >   (pa-risc)
> > >      p Math.log10(10_000)
> > >      3.9999999999999996
> > 
> > Build and run following C code:
> > 
> > % cat f.c
> > #include <math.h>
> > #include <stdio.h>
> > 
> > int main(void) {
> >   printf("%a\n", log10(10000));
> >   return 0;
> > }
> > %  gcc -lm f.c && ./a.out
> > 0x1p+2 (or something)
> 
> $ cat t.c
> #include <math.h>
> #include <stdio.h>
> 
> int main(void) {
>   printf("%f\n", log10(10000));
>   printf("%a\n", log10(10000));
>   return 0; 
> }
> 
> (ia64)
>   $ cc +O1 +Ofltacc +Olit=all +Oentrysched +Odataprefetch -lm t.c
>   $ ./a.out
>   4.000000
>   0x1.0000000000000p+2
> 
> %a is only supported on HP-UX/IA systems, not HP-UX/PA. We're using the HP-UX C compiler to build Ruby as well.
> ----------------------------------------
> Bug #5497: Math.log10(10_000) error on HP-UX/PA
> http://redmine.ruby-lang.org/issues/5497
> 
> Author: The Written Word Inc
> Status: Open
> Priority: Normal
> Assignee: 
> Category: core
> Target version: 1.9.2
> ruby -v: UNKNOWN
> 
> 
> I've built 1.9.2 from svn revision at 33531 on HP-UX/PA and HP-UX/IA. I'm getting two different results for Math.log10(10_000) depending on IA64 and PA-RISC:
>   (ia64)
>      p Math.log10(10_000)
>      4
>   (pa-risc)
>      p Math.log10(10_000)
>      3.9999999999999996
> 
> Any idea where in the code I can look to try and fix this?
> 
> 
> -- 
> http://redmine.ruby-lang.org

-- 

loop found in loop in redundant loopback