make use of __builtin_isnanf

[Bruno Haible]

GCC 4.0 or newer has a built-in for isnanf(). This patch makes use of it
(overriding the libc's isnanf(), since the GCC built-in appears to work
everywhere).

2008-01-26  Bruno Haible  <address@hidden>

        * m4/isnanf.m4 (gl_HAVE_ISNANF_NO_LIBM, gl_ISNANF_WORKS): Test the
        GCC >= 4.0 built-in.
        * lib/isnanf.h (isnanf): Use the GCC >= 4.0 built-in.

*** lib/isnanf.h.orig   2008-01-26 13:20:12.000000000 +0100
--- lib/isnanf.h        2008-01-26 13:19:50.000000000 +0100
***************
*** 1,5 ****
  /* Test for NaN that does not need libm.
!    Copyright (C) 2007 Free Software Foundation, Inc.
  
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
--- 1,5 ----
  /* Test for NaN that does not need libm.
!    Copyright (C) 2007-2008 Free Software Foundation, Inc.
  
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
***************
*** 17,23 ****
  #if HAVE_ISNANF_IN_LIBC
  /* Get declaration of isnan macro or (older) isnanf function.  */
  # include <math.h>
! # ifdef isnan
  #  undef isnanf
  #  define isnanf(x) isnan ((float)(x))
  # endif
--- 17,27 ----
  #if HAVE_ISNANF_IN_LIBC
  /* Get declaration of isnan macro or (older) isnanf function.  */
  # include <math.h>
! # if __GNUC__ >= 4
!    /* GCC 4.0 and newer provides three built-ins for isnan.  */
! #  undef isnanf
! #  define isnanf(x) __builtin_isnanf ((float)(x))
! # elif defined isnan
  #  undef isnanf
  #  define isnanf(x) isnan ((float)(x))
  # endif
*** m4/isnanf.m4.orig   2008-01-26 13:20:12.000000000 +0100
--- m4/isnanf.m4        2008-01-26 13:19:50.000000000 +0100
***************
*** 1,5 ****
! # isnanf.m4 serial 4
! dnl Copyright (C) 2007 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
  dnl with or without modifications, as long as this notice is preserved.
--- 1,5 ----
! # isnanf.m4 serial 5
! dnl Copyright (C) 2007-2008 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
  dnl with or without modifications, as long as this notice is preserved.
***************
*** 33,39 ****
      [gl_cv_func_isnanf_no_libm],
      [
        AC_TRY_LINK([#include <math.h>
!                    #ifdef isnan
                     # undef isnanf
                     # define isnanf(x) isnan ((float)(x))
                     #endif
--- 33,42 ----
      [gl_cv_func_isnanf_no_libm],
      [
        AC_TRY_LINK([#include <math.h>
!                    #if __GNUC__ >= 4
!                    # undef isnanf
!                    # define isnanf(x) __builtin_isnanf ((float)(x))
!                    #elif defined isnan
                     # undef isnanf
                     # define isnanf(x) isnan ((float)(x))
                     #endif
***************
*** 54,60 ****
      [
        AC_TRY_RUN([
  #include <math.h>
! #ifdef isnan
  # undef isnanf
  # define isnanf(x) isnan ((float)(x))
  #endif
--- 57,66 ----
      [
        AC_TRY_RUN([
  #include <math.h>
! #if __GNUC__ >= 4
! # undef isnanf
! # define isnanf(x) __builtin_isnanf ((float)(x))
! #elif defined isnan
  # undef isnanf
  # define isnanf(x) isnan ((float)(x))
  #endif