Re: new module 'fpieee'

[Ben Pfaff]

Bruno Haible <address@hidden> writes:

> The code needed for isnan() needs to construct a NaN or Inf object. But
> doing so leads to a SIGFPE by default on Alpha systems. There's only one
> way to get IEEE compliant behaviour of elementary arithmetic operations on
> this platform: instruct the compiler to emit different (more expensive)
> floating-point instructions. This module implements it.

Is this also necessary on SH systems?  The GCC manual has this in
the page specific to SH:

    `-mieee'
         Increase IEEE-compliance of floating-point code.  At the moment,
         this is equivalent to `-fno-finite-math-only'.  When generating 16
         bit SH opcodes, getting IEEE-conforming results for comparisons of
         NANs / infinities incurs extra overhead in every floating point
         comparison, therefore the default is set to `-ffinite-math-only'.

In GNU PSPP, I have a configure test that just checks whether the
compiler accepts -mieee and uses it if it is available.  I wonder
whether this is an approach that is more likely to automatically
work as architectures appear.

Here's what PSPP is using:

    dnl Check whether a C compiler option is accepted.
    dnl If so, add it to CFLAGS.
    dnl Example: PSPP_ENABLE_OPTION(-Wdeclaration-after-statement)
    AC_DEFUN([PSPP_ENABLE_OPTION],
    [
      m4_define([pspp_cv_name], [pspp_cv_[]m4_translit([$1], [-], [_])])dnl
      AC_CACHE_CHECK([whether $CC accepts $1], [pspp_cv_name], 
        [pspp_save_CFLAGS="$CFLAGS"
         CFLAGS="$CFLAGS $1"
         AC_COMPILE_IFELSE([AC_LANG_PROGRAM(,)], [pspp_cv_name[]=yes], 
[pspp_cv_name[]=no])
         CFLAGS="$pspp_save_CFLAGS"])
      if test $pspp_cv_name = yes; then
        CFLAGS="$CFLAGS $1"
      fi
    ])

...

    PSPP_ENABLE_OPTION(-mieee)
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