Re: new module 'isnan-nolibm'

[Bruno Haible]

Eric Blake wrote:
> No, on cygwin, isnan is a macro in <math.h> that wraps the internal
> functions __isnan{,lf}, and the isnan entry point in cygwin1.dll exists
> only for backwards compatibility for multi-year-old apps that were
> compiled against cygwin prior to the POSIX compliance bug being fixed of
> providing isnan only as a macro.

My copy of cygwin <math.h> (dated 2006-01-20) still has
   extern int isnan _PARAMS((double));
You simply have a newer copy of cygwin than me.

> And you still didn't catch my point that
> on cygwin, you don't need -lm to get isnan() to work

Since there are also AIX, OSF/1, HP-UX, the situation on cygwin has no
effect on m4/isnan.m4.

> Checking AC_CHECK_FUNC([isnan]) is
> wrong since POSIX does not guarantee that isnan is a function; instead,
> you must check whether including <math.h> and using isnan() will link
> correctly in the absence of -lm.

Oh, I see now what you mean. Thanks for insisting. I had based my
understanding of these functions on a manual page that lists isnanf(),
isnan() as a function, and isnanl(). Doing as you say.

Bruno


2007-02-24  Bruno Haible  <address@hidden>

        * lib/isnanl.h (isnanl): Define through isnan if isnan is a macro.
        * m4/isnan.m4 (gl_FUNC_ISNAN_NO_LIBM): Don't check for isnan as a
        function; instead check whether isnan with a double argument links.
        * m4/isnanl.m4 (gl_FUNC_ISNANL_NO_LIBM): Don't check for isnanl as a
        function; instead check whether isnan with a 'long double' argument
        links.
        Reported by Eric Blake <address@hidden>.

*** lib/isnan.h 24 Feb 2007 19:08:56 -0000      1.1
--- lib/isnan.h 25 Feb 2007 04:38:13 -0000
***************
*** 16,22 ****
     Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  
  #if HAVE_ISNAN_IN_LIBC
! /* Get declaration of isnan.  */
  # include <math.h>
  #else
  /* Test whether X is a NaN.  */
--- 16,22 ----
     Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  
  #if HAVE_ISNAN_IN_LIBC
! /* Get declaration of isnan macro.  */
  # include <math.h>
  #else
  /* Test whether X is a NaN.  */
*** lib/isnanl.h        24 Feb 2007 19:15:21 -0000      1.1
--- lib/isnanl.h        25 Feb 2007 04:38:13 -0000
***************
*** 16,23 ****
     Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  
  #if HAVE_ISNANL_IN_LIBC
! /* Get declaration of isnanl.  */
  # include <math.h>
  #else
  /* Test whether X is a NaN.  */
  # undef isnanl
--- 16,27 ----
     Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  
  #if HAVE_ISNANL_IN_LIBC
! /* Get declaration of isnan macro or (older) isnanl function.  */
  # include <math.h>
+ # ifdef isnan
+ #  undef isnanl
+ #  define isnanl(x) isnan ((long double)(x))
+ # endif
  #else
  /* Test whether X is a NaN.  */
  # undef isnanl
*** m4/isnan.m4 25 Feb 2007 01:57:58 -0000      1.2
--- m4/isnan.m4 25 Feb 2007 04:38:13 -0000
***************
*** 8,19 ****
  
  AC_DEFUN([gl_FUNC_ISNAN_NO_LIBM],
  [
!   AC_CHECK_FUNC([isnan],
!     [gl_cv_func_isnan_no_libm=yes],
!     [gl_cv_func_isnan_no_libm=no])
    if test $gl_cv_func_isnan_no_libm = yes; then
      AC_DEFINE([HAVE_ISNAN_IN_LIBC], 1,
!       [Define if the isnan() function is available in libc.])
    else
      AC_LIBOBJ([isnan])
      gl_DOUBLE_EXPONENT_LOCATION
--- 8,25 ----
  
  AC_DEFUN([gl_FUNC_ISNAN_NO_LIBM],
  [
!   AC_CACHE_CHECK([whether isnan(double) can be used without linking with 
libm],
!     [gl_cv_func_isnan_no_libm],
!     [
!       AC_TRY_LINK([#include <math.h>
!                    double x;],
!                   [return isnan (x);],
!         [gl_cv_func_isnan_no_libm=yes],
!         [gl_cv_func_isnan_no_libm=no])
!     ])
    if test $gl_cv_func_isnan_no_libm = yes; then
      AC_DEFINE([HAVE_ISNAN_IN_LIBC], 1,
!       [Define if the isnan(double) function is available in libc.])
    else
      AC_LIBOBJ([isnan])
      gl_DOUBLE_EXPONENT_LOCATION
*** m4/isnanl.m4        24 Feb 2007 19:15:21 -0000      1.1
--- m4/isnanl.m4        25 Feb 2007 04:38:13 -0000
***************
*** 8,19 ****
  [
    AC_REQUIRE([gt_TYPE_LONGDOUBLE])
    if test $gt_cv_c_long_double = yes; then
!     AC_CHECK_FUNC([isnanl],
!       [gl_cv_func_isnanl_no_libm=yes],
!       [gl_cv_func_isnanl_no_libm=no])
      if test $gl_cv_func_isnanl_no_libm = yes; then
        AC_DEFINE([HAVE_ISNANL_IN_LIBC], 1,
!         [Define if the isnanl() function is available in libc.])
      else
        AC_LIBOBJ([isnanl])
        gl_LONG_DOUBLE_EXPONENT_LOCATION
--- 8,29 ----
  [
    AC_REQUIRE([gt_TYPE_LONGDOUBLE])
    if test $gt_cv_c_long_double = yes; then
!     AC_CACHE_CHECK([whether isnan(long double) can be used without linking 
with libm],
!       [gl_cv_func_isnanl_no_libm],
!       [
!         AC_TRY_LINK([#include <math.h>
!                      #ifdef isnan
!                      # undef isnanl
!                      # define isnanl(x) isnan ((long double)(x))
!                      #endif
!                      long double x;],
!                     [return isnanl (x);],
!           [gl_cv_func_isnanl_no_libm=yes],
!           [gl_cv_func_isnanl_no_libm=no])
!       ])
      if test $gl_cv_func_isnanl_no_libm = yes; then
        AC_DEFINE([HAVE_ISNANL_IN_LIBC], 1,
!         [Define if the isnan(long double) function is available in libc.])
      else
        AC_LIBOBJ([isnanl])
        gl_LONG_DOUBLE_EXPONENT_LOCATION