Re: [PATCH] Don't do double divide in powf.

[Corinna Vinschen <vinschen at redhat dot com>]

On Dec 11 19:45, Jim Wilson wrote:
> Similar to the previous powf patch, we have a double 0.0/0.0 divide being
> used to generate a NaN, which on a single float only target pulls in divdf3.
> wf_log.c calls nan instead.  I fixed powf to do the same.
> 
> With this patch, and a small testcase, I see
> 
> gamma02:2368$ ls -lt a.out*
> -rwxrwxr-x 1 jimw jimw 32912 Dec 11 19:35 a.out
> -rwxrwxr-x 1 jimw jimw 46992 Dec 11 18:54 a.out.unpatched
> gamma02:2369$ 
> 
> So the patched code is about 70% of the size of the unpatched code.
> 
> This was tested with the testcase included below, and a newlib make check.
> 
> Jim
> 
> 	newlib/
> 	* libm/math/wf_pow.c (powf): Call nan instead of double 0.0/0.0.
> ---
>  newlib/libm/math/wf_pow.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/newlib/libm/math/wf_pow.c b/newlib/libm/math/wf_pow.c
> index be453558b..1e0447173 100644
> --- a/newlib/libm/math/wf_pow.c
> +++ b/newlib/libm/math/wf_pow.c
> @@ -108,7 +108,7 @@
>  		    if (_LIB_VERSION == _SVID_) 
>  		        exc.retval = 0.0;
>  		    else 
> -		        exc.retval = 0.0/0.0;	/* X/Open allow NaN */
> +		        exc.retval = nan("");	/* X/Open allow NaN */

As far as I can see, that still pulls in an unnecessary function call,
nan().

What about using NAN?  That's basically __builtin_nanf("") and usually
resolves without function call on any platform.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

Attachment: signature.asc
Description: PGP signature