frexpl: detect BeOS bug

[Bruno Haible]

The BeOS frexpl() function is broken: it does not work for x = 2^(i-1)
where LDBL_MAX_EXP-62 <= i <= LDBL_MAX_EXP. This detects it, so that
gnulib's frexpl() substitute is used instead.


2007-05-20  Bruno Haible  <address@hidden>

        * m4/frexpl.m4 (gl_FUNC_FREXPL_WORKS): Add test for large finite
        numbers that fails on BeOS.
        * doc/functions/frexpl.texi: Update.

*** doc/functions/frexpl.texi   1 May 2007 17:59:19 -0000       1.2
--- doc/functions/frexpl.texi   20 May 2007 09:57:40 -0000
***************
*** 13,19 ****
  FreeBSD 5.2.1, NetBSD 3.0, OpenBSD 3.8, HP-UX 11, IRIX 6.5, Solaris 9, 
Cygwin, Interix 3.5.
  @item
  This function does not work on finite numbers on some platforms:
! AIX 5.1.
  @item
  This function does not work on infinite numbers on some platforms:
  IRIX 6.5.
--- 13,19 ----
  FreeBSD 5.2.1, NetBSD 3.0, OpenBSD 3.8, HP-UX 11, IRIX 6.5, Solaris 9, 
Cygwin, Interix 3.5.
  @item
  This function does not work on finite numbers on some platforms:
! AIX 5.1, BeOS.
  @item
  This function does not work on infinite numbers on some platforms:
  IRIX 6.5.
*** m4/frexpl.m4        20 May 2007 08:19:54 -0000      1.9
--- m4/frexpl.m4        20 May 2007 09:57:41 -0000
***************
*** 1,4 ****
! # frexpl.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,
--- 1,4 ----
! # frexpl.m4 serial 5
  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,
***************
*** 95,102 ****
    fi
  ])
  
! dnl Test whether frexpl() works on finite numbers (this fails on AIX 5.1) and
! dnl also on infinite numbers (this fails e.g. on IRIX 6.5).
  AC_DEFUN([gl_FUNC_FREXPL_WORKS],
  [
    AC_REQUIRE([AC_PROG_CC])
--- 95,102 ----
    fi
  ])
  
! dnl Test whether frexpl() works on finite numbers (this fails on AIX 5.1 and
! dnl on BeOS) and also on infinite numbers (this fails e.g. on IRIX 6.5).
  AC_DEFUN([gl_FUNC_FREXPL_WORKS],
  [
    AC_REQUIRE([AC_PROG_CC])
***************
*** 117,122 ****
--- 117,136 ----
      if (exp != 5)
        return 1;
    }
+   /* Test on large finite numbers.  This fails on BeOS at i = 16322, while
+      LDBL_MAX_EXP = 16384.
+      In the loop end test, we test x against Infinity, rather than comparing
+      i with LDBL_MAX_EXP, because BeOS <float.h> has a wrong LDBL_MAX_EXP.  */
+   {
+     int i;
+     for (i = 1, x = 1.0L; x != x + x; i++, x *= 2.0L)
+       {
+         int exp = -9999;
+         frexpl (x, &exp);
+         if (exp != i)
+           return 1;
+       }
+   }
    /* Test on infinite numbers.  */
    x = 1.0L / 0.0L;
    {
***************
*** 128,135 ****
    return 0;
  }], [gl_cv_func_frexpl_works=yes], [gl_cv_func_frexpl_works=no],
        [case "$host_os" in
!          aix* | irix*) gl_cv_func_frexpl_works="guessing no";;
!          *)            gl_cv_func_frexpl_works="guessing yes";;
         esac
        ])
      ])
--- 142,149 ----
    return 0;
  }], [gl_cv_func_frexpl_works=yes], [gl_cv_func_frexpl_works=no],
        [case "$host_os" in
!          aix* | beos* | irix*) gl_cv_func_frexpl_works="guessing no";;
!          *)                    gl_cv_func_frexpl_works="guessing yes";;
         esac
        ])
      ])