ilogb manpage

ilogb manpage

[Will Newton]

Hi,

The ilogb manpage currently claims that errno is not set on error:

       Domain error: x is 0 or a NaN
              An invalid floating-point exception (FE_INVALID) is raised.

              These functions do not set errno for this case.

       Domain error: x is an infinity

              These functions do not set errno or raise an exception
for this case.

However this is at odds with the ISO C standard an the most recent glibc code:

int
__ilogb (double x)
{
  int r = __ieee754_ilogb (x);
  if (__builtin_expect (r == FP_ILOGB0, 0)
      || __builtin_expect (r == FP_ILOGBNAN, 0)
      || __builtin_expect (r == INT_MAX, 0))
    {
      __set_errno (EDOM);
      feraiseexcept (FE_INVALID);
    }
  return r;
}


-- 
Will Newton
Toolchain Working Group, Linaro
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Re: ilogb manpage

[Michael Kerrisk (man-pages)]

Hi Will,

On 10/29/2014 01:18 PM, Will Newton wrote:
> Hi,
> 
> The ilogb manpage currently claims that errno is not set on error:
> 
>        Domain error: x is 0 or a NaN
>               An invalid floating-point exception (FE_INVALID) is raised.
> 
>               These functions do not set errno for this case.
> 
>        Domain error: x is an infinity
> 
>               These functions do not set errno or raise an exception
> for this case.
> 
> However this is at odds with the ISO C standard an the most recent glibc code:
> 
> int
> __ilogb (double x)
> {
>   int r = __ieee754_ilogb (x);
>   if (__builtin_expect (r == FP_ILOGB0, 0)
>       || __builtin_expect (r == FP_ILOGBNAN, 0)
>       || __builtin_expect (r == INT_MAX, 0))
>     {
>       __set_errno (EDOM);
>       feraiseexcept (FE_INVALID);
>     }
>   return r;
> }

Thanks for the report. Things were fixed in glibc 2.16
( https://www.sourceware.org/bugzilla/show_bug.cgi?id=6794 )
and I've now updated the man page.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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