changeset 16321:1031e29cf9ff

stdalign: relax _Alignof and tighten _Alignas test * m4/stdalign.m4 (gl_STDALIGN_H): Relax the _Alignof test, as it was too strict: alignof must divide offsetof, but it need not equal offsetof. Inspired by Joseph S. Myers's comment <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023#c10>. Conversely, tighten the _Alignas test a bit, as the resulting alignment must be exactly 8.
author Paul Eggert <eggert@cs.ucla.edu>
date Fri, 27 Jan 2012 22:17:42 -0800
parents fb33caa0a0ce
children 7256be967b3a
files ChangeLog m4/stdalign.m4
diffstat 2 files changed, 14 insertions(+), 3 deletions(-) [+]
line wrap: on
line diff
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2012-01-27  Paul Eggert  <eggert@cs.ucla.edu>
+
+	stdalign: relax _Alignof and tighten _Alignas test
+	* m4/stdalign.m4 (gl_STDALIGN_H): Relax the _Alignof test,
+	as it was too strict: alignof must divide offsetof, but it need
+	not equal offsetof.  Inspired by Joseph S. Myers's comment
+	<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023#c10>.
+	Conversely, tighten the _Alignas test a bit, as the resulting
+	alignment must be exactly 8.
+
 2012-01-27  Bruno Haible  <bruno@clisp.org>
 
 	stdalign: Document the last change.
--- a/m4/stdalign.m4
+++ b/m4/stdalign.m4
@@ -25,15 +25,16 @@
             #else
             # define ao(type) offsetof (struct { char a; type b; }, b)
             #endif
-            char test1[_Alignof (double) == ao (double) ? 1 : -1];
-            char test2[alignof (long int) == ao (long int) ? 1 : -1];
+            char test_double[ao (double) % _Alignof (double) == 0 ? 1 : -1];
+            char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1];
+            char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1];
 
             /* Test _Alignas only on platforms where gnulib can help.  */
             #if \
                 (__GNUC__ || __IBMC__ || __IBMCPP__ \
                  || 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
               int alignas (8) alignas_int = 1;
-              char test3[8 <= _Alignof (alignas_int) ? 1 : -1];
+              char test_alignas[_Alignof (alignas_int) == 8 ? 1 : -1];
             #endif
           ]])],
        [gl_cv_header_working_stdalign_h=yes],