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

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

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.