closes bpo-33512: use standard for detecting long double (GH-6847)

Misc/NEWS.d/next/Build/2018-05-15-02-07-49.bpo-33512.X4Fy1Q.rst

+configure's check for "long double" has been simplified

configure

@@ -779,7 +779,6 @@ infodir
 docdir
 oldincludedir
 includedir
-runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -887,7 +886,6 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
-runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -1140,15 +1138,6 @@ do
   | -silent | --silent | --silen | --sile | --sil)
     silent=yes ;;
 
-  -runstatedir | --runstatedir | --runstatedi | --runstated \
-  | --runstate | --runstat | --runsta | --runst | --runs \
-  | --run | --ru | --r)
-    ac_prev=runstatedir ;;
-  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
-  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
-  | --run=* | --ru=* | --r=*)
-    runstatedir=$ac_optarg ;;
-
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1286,7 +1275,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir runstatedir
+		libdir localedir mandir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -1439,7 +1428,6 @@ Fine tuning of the installation directories:
   --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
   --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
   --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
-  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
   --libdir=DIR            object code libraries [EPREFIX/lib]
   --includedir=DIR        C header files [PREFIX/include]
   --oldincludedir=DIR     C header files for non-gcc [/usr/include]
@@ -8603,32 +8591,48 @@ _ACEOF
 
 
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for long double support" >&5
-$as_echo_n "checking for long double support... " >&6; }
-have_long_double=no
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
 
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for long double" >&5
+$as_echo_n "checking for long double... " >&6; }
+if ${ac_cv_type_long_double+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test "$GCC" = yes; then
+       ac_cv_type_long_double=yes
+     else
+       cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+/* The Stardent Vistra knows sizeof (long double), but does
+		 not support it.  */
+	      long double foo = 0.0L;
 int
 main ()
 {
-long double x; x = (long double)0;
+static int test_array [1 - 2 * !(/* On Ultrix 4.3 cc, long double is 4 and double is 8.  */
+	      sizeof (double) <= sizeof (long double))];
+test_array [0] = 0;
+return test_array [0];
+
   ;
   return 0;
 }
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
-
+  ac_cv_type_long_double=yes
+else
+  ac_cv_type_long_double=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+     fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_type_long_double" >&5
+$as_echo "$ac_cv_type_long_double" >&6; }
+  if test $ac_cv_type_long_double = yes; then
 
 $as_echo "#define HAVE_LONG_DOUBLE 1" >>confdefs.h
 
-  have_long_double=yes
+  fi
 
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $have_long_double" >&5
-$as_echo "$have_long_double" >&6; }
-if test "$have_long_double" = yes ; then
 # The cast to long int works around a bug in the HP C Compiler
 # version HP92453-01 B.11.11.23709.GP, which incorrectly rejects
 # declarations like `int a3[[(sizeof (unsigned char)) >= 0]];'.
@@ -8662,7 +8666,6 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
-fi
 
 # The cast to long int works around a bug in the HP C Compiler
 # version HP92453-01 B.11.11.23709.GP, which incorrectly rejects

configure.ac

@@ -2198,16 +2198,8 @@ AC_CHECK_SIZEOF(size_t, 4)
 AC_CHECK_SIZEOF(pid_t, 4)
 AC_CHECK_SIZEOF(uintptr_t)
 
-AC_MSG_CHECKING(for long double support)
-have_long_double=no
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[long double x; x = (long double)0;]])],[
-  AC_DEFINE(HAVE_LONG_DOUBLE, 1, [Define this if you have the type long double.])
-  have_long_double=yes
-],[])
-AC_MSG_RESULT($have_long_double)
-if test "$have_long_double" = yes ; then
+AC_TYPE_LONG_DOUBLE
 AC_CHECK_SIZEOF(long double, 16)
-fi
 
 AC_CHECK_SIZEOF(_Bool, 1)
 

pyconfig.h.in

@@ -617,7 +617,7 @@
 /* Define to 1 if you have the `log2' function. */
 #undef HAVE_LOG2
 
-/* Define this if you have the type long double. */
+/* Define to 1 if the system has the type `long double'. */
 #undef HAVE_LONG_DOUBLE
 
 /* Define to 1 if you have the `lstat' function. */