Re: [PATCH] Fix error in fdim/f for infinities

Corinna Vinschen <[email protected]> Tue, 10 Mar 2020 15:47:14 +0100

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

On Mar 10 11:24, Fabian Schriever wrote:
> The comparison c == FP_INFINITE causes the function to return +inf as it
> expects x = +inf to always be larger than y. This shortcut causes
> several issues as it also returns +inf for the following cases:
>  - fdim(+inf, +inf), expected (as per C99): +0.0
>  - fdim(-inf, any non NaN), expected: +0.0
> 
> I don't see a reason to keep the comparison as all the infinity cases
> return the correct result using just the ternary operation.
> ---
>  newlib/libm/common/s_fdim.c  | 5 +----
>  newlib/libm/common/sf_fdim.c | 5 +----
>  2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/newlib/libm/common/s_fdim.c b/newlib/libm/common/s_fdim.c
> index 73a027953..61a4908f3 100644
> --- a/newlib/libm/common/s_fdim.c
> +++ b/newlib/libm/common/s_fdim.c
> @@ -49,11 +49,8 @@ ANSI C, POSIX.
>  	double y;
>  #endif
>  {
> -  int c = __fpclassifyd(x);
> -  if (c == FP_NAN)  return(x);
> +  if (__fpclassifyd(x) == FP_NAN)  return(x);
>    if (__fpclassifyd(y) == FP_NAN)  return(y);
> -  if (c == FP_INFINITE)
> -    return HUGE_VAL;
>  
>    return x > y ? x - y : 0.0;
>  }
> diff --git a/newlib/libm/common/sf_fdim.c b/newlib/libm/common/sf_fdim.c
> index fe349098b..8fee57002 100644
> --- a/newlib/libm/common/sf_fdim.c
> +++ b/newlib/libm/common/sf_fdim.c
> @@ -14,11 +14,8 @@
>  	float y;
>  #endif
>  {
> -  int c = __fpclassifyf(x);
> -  if (c == FP_NAN)  return(x);
> +  if (__fpclassifyf(x) == FP_NAN)  return(x);
>    if (__fpclassifyf(y) == FP_NAN)  return(y);
> -  if (c == FP_INFINITE)
> -    return HUGE_VALF;
>  
>    return x > y ? x - y : 0.0;
>  }
> -- 
> 2.24.1.windows.2
> 

Pushed.

Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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