re: port-sparc64/47834: 128 bit softfloat scalbnl broken

[matthew green <mrg%eterna.com.au@localhost>]

The following reply was made to PR port-sparc64/47834; it has been noted by 
GNATS.

From: matthew green <mrg%eterna.com.au@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: port-sparc64-maintainer%netbsd.org@localhost, 
gnats-admin%netbsd.org@localhost,
    netbsd-bugs%netbsd.org@localhost
Subject: re: port-sparc64/47834: 128 bit softfloat scalbnl broken
Date: Sun, 19 May 2013 15:48:56 +1000

 your test program isn't entirely correct.
 
 > Running the below test program (natively compiled on sparc64) reports
 > different, but all wrong numeric results depending on the optimization
 > level used.
 > 
 > With -O0 it says:
 >      0 (should be: 1.00085)
 
 this is bad.
 
 > Letting the compiler pre-compute it with -O2 it says:
 >      2.0017 (should be: 1.00085)
 
 this result is correct.  FLT_RADIX is 2, and:
 
 DESCRIPTION
      The scalbn(), scalbnf(), and scalbnl() functions compute x * r^n, where r
      is the radix of the machine's floating point arithmetic, defined by the
      FLT_RADIX constant in <float.h>.  The rationale is efficiency; r^n is not
 
 ie, we have:  1.00085 * 2^1 => 2.0017.
 
 > >How-To-Repeat:
 > Natively compile this program (with -lm) on sparc64:
 > 
 > #include <math.h>
 > #include <stdio.h>
 > 
 > int main(int argc, char **argv)
 > {
 >      long double val = 1.00085;
 >      long double res = scalbnl(val, 1);
 > 
 >      printf("%Lg (should be: %Lg)\n", res, val);
 > 
 >      return 0;
 > }
 
 
 .mrg.