From ba7b7388f820b620ad4f92d263f7037dd7c89bfc Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Fri, 27 Jan 2012 22:17:42 -0800 Subject: [PATCH] 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 . Conversely, tighten the _Alignas test a bit, as the resulting alignment must be exactly 8. --- ChangeLog | 10 ++++++++++ m4/stdalign.m4 | 7 ++++--- 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/ChangeLog b/ChangeLog index 399be2e83..b5fd92e5f 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,13 @@ +2012-01-27 Paul Eggert + + 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 + . + Conversely, tighten the _Alignas test a bit, as the resulting + alignment must be exactly 8. + 2012-01-27 Bruno Haible stdalign: Document the last change. diff --git a/m4/stdalign.m4 b/m4/stdalign.m4 index d78a58980..6659c9c3e 100644 --- a/m4/stdalign.m4 +++ b/m4/stdalign.m4 @@ -25,15 +25,16 @@ AC_DEFUN([gl_STDALIGN_H], #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], -- 2.11.0