[parisc-linux] Re: strtold

[John David Anglin]

> strtold will never work, gcc and libc have different sizes for long
> double. This is probably a side-effect of this.

I'm not sure what has changed but this is the source of a number
of gfortran and libstdc++ regressions when using the current version
of libc in unstable.

> If we really want long double to work we need to do something like set
> it to be the same as double.

Long double has always been the same as double in GCC.  It allowed
by the C and C++ standards.  It fast and the hardware and corner
cases are well understood.

I've given up hope that HP will release their IEEE long double emulation
code for PA-RISC.  Although I don't have any hard evidence of bugs in it,
there is the suggestion from the ada testsuite run under hpux that there
may be bugs in the rounding and exception support.

> 128-bit long double is just going to be a pain, and I don't know how
> well the 80-bit long double from IBM supports IEEE modes.

The only viable alternatives at this point are:

  1) long double == double (64 bit long double), or
  2) IBM 128-bit double double implementation used by powerpc.

After more than a year of using the double-double format, the powerpc
folks are still working the bugs out from the corner cases.  While I
guess it more or less works, I wouldn't want to rely on it for
critical calculations.  RTH recented indicated that this would be a
poor choice for another port in the same situation.  The same viewpoint
was expressed to me by an Ada maintainer at the last GCC summit.  Ada
probably has the best numerics support in GCC.

There is no support for the 80-bit format (either in hardware or
software) on PA-RISC as far as I know.  So, this alternative isn't viable.

C99 requires long double support.  Thus, I believe we should go with
option 1 and libc should be changed.  We aren't the only target with
this problem, so there must be some libc support for 64-bit long double.

Dave
-- 
J. David Anglin                                  dave.anglin at nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)