Re: [PATCH] newlib: switch to autoconf long double wider macro

[Corinna Vinschen <vinschen@redhat.com>]

On Jan 21 07:39, Mike Frysinger wrote:
> On 21 Jan 2022 12:27, Corinna Vinschen wrote:
> > On Jan 21 00:04, Mike Frysinger wrote:
> > > Now that we require a recent version of autoconf, we can rely on this
> > > macro existing.  It has inverted semantics from the existing test (it
> > > looks for "is wider" instead of "is equal"), so we have to invert the
> > > check when creating our _LDBL_EQ_DBL.
> > > ---
> > >  newlib/configure    | 72 +++++++++++++++++++++++++++++----------------
> > >  newlib/configure.ac | 22 ++------------
> > >  newlib/newlib.hin   |  4 +++
> > >  3 files changed, 53 insertions(+), 45 deletions(-)
> > 
> > Looks right to me, please push.
> 
> for posterity, i'll note that autoconf uses a different (more comprehensive)
> testing method that ultimately arrives at a diff answer than what newlib is
> atm.  for aarch64, _LDBL_EQ_DBL is now defined when it wasn't before.
> 
> newlib today is doing:
> #if DBL_MANT_DIG == LDBL_MANT_DIG && \
>     LDBL_MIN_EXP == DBL_MIN_EXP   && \
>     LDBL_MAX_EXP == DBL_MAX_EXP
>   #define _LDBL_EQ_DBL
>  #else
>   #error "LDBL != DBL"
> #endif
> 
> while autoconf is doing:
>        (0 < ((DBL_MAX_EXP < LDBL_MAX_EXP)
>           + (DBL_MANT_DIG < LDBL_MANT_DIG)
>           - (LDBL_MAX_EXP < DBL_MAX_EXP)
>           - (LDBL_MANT_DIG < DBL_MANT_DIG)))
>        && (int) LDBL_EPSILON == 0
> -mike

Erm... that's kind of weird.  The newlib expression doesn't look wrong.

So, out of curiosity of somebody not being familiar with aarch64,
why is that?


Corinna