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Re: [PATCH 2.19] BZ16427: Fix ldbl-128 exp overflows


On Tue, Jan 14, 2014 at 09:29:48AM +0100, Andreas Krebbel wrote:
> 2014-01-14  Andreas Krebbel  <Andreas.Krebbel@de.ibm.com>
> 
> 	[BZ #16427]
> 	* sysdeps/ieee754/ldbl-128/w_expl.c (__expl): Invoke the non-IEEE
> 	handling only for numbers special also in the IEEE case.
> 
> commit 1e74b6daed6c95628a4710f64d140880457c9c44
> Author: Andreas Krebbel <krebbel@linux.vnet.ibm.com>
> Date:   Mon Jan 13 14:41:47 2014 +0000
> 
>     S/390: Fix ldbl-128 exp overflows.

Please put in a more descriptive commit message and mention the bz# in
the subject line of the message so that the post-hook adds a comment
to the bug report.

> 
> diff --git a/sysdeps/ieee754/ldbl-128/w_expl.c b/sysdeps/ieee754/ldbl-128/w_expl.c
> index 10193be..af37aba 100644
> --- a/sysdeps/ieee754/ldbl-128/w_expl.c
> +++ b/sysdeps/ieee754/ldbl-128/w_expl.c
> @@ -25,24 +25,16 @@ static char rcsid[] = "$NetBSD: $";
>  #include <math.h>
>  #include <math_private.h>
>  
> -static const long double
> -o_threshold= 1.1356523406294143949491931077970763428449E4L,
> -u_threshold= -1.1433462743336297878837243843452621503410E4;
> -
>  long double __expl(long double x)	/* wrapper exp */
>  {
>  #ifdef _IEEE_LIBM
>  	return __ieee754_expl(x);
>  #else
> -	long double z;
> -	z = __ieee754_expl(x);
> -	if(_LIB_VERSION == _IEEE_) return z;
> -	if(__finitel(x)) {
> -	    if(x>o_threshold)
> -	        return __kernel_standard_l(x,x,206); /* exp overflow */
> -	    else if(x<u_threshold)
> -	        return __kernel_standard_l(x,x,207); /* exp underflow */
> -	}
> +	long double z = __ieee754_expl (x);
> +	if (__builtin_expect (!__finitel (z) || z == 0, 0)

Use __glibc_unlikely.

> +	    && __finitel (x) && _LIB_VERSION != _IEEE_)
> +	  return __kernel_standard_l (x, x, 206 + !!__signbitl (x));
> +
>  	return z;
>  #endif
>  }
> 

Siddhesh


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