Add `scm_t_aligned_cell' internal type.

[bpt/guile.git] / libguile / _scm.h

diff --git a/libguile/_scm.h b/libguile/_scm.h
index 3bb78b4..f18b3a8 100644 (file)
--- a/libguile/_scm.h
+++ b/libguile/_scm.h
@@ -63,6 +63,7 @@
 
 #include <errno.h>
 #include <verify.h>
+#include <alignof.h>
 #include "libguile/__scm.h"
 
 /* Include headers for those files central to the implementation.  The
@@ -192,6 +193,35 @@
 #define SCM_OBJCODE_COOKIE                              \
   "GOOF-" SCM_OBJCODE_MACHINE_VERSION_STRING "---"
 
+\f
+/* Cells have to be 8-byte aligned.  Use `scm_t_aligned_cell' when not
+   allocating on the heap to have this guarantee.  This is similar to the
+   `SCM_ALIGNED' macro but provides an option likely to work with compilers
+   other than GCC.  */
+
+#ifdef __GNUC__
+
+struct scm_aligned_cell
+{
+  scm_t_cell cell __attribute__ ((__aligned__ (8)));
+};
+
+typedef struct scm_aligned_cell scm_t_aligned_cell;
+
+#else /* !__GNUC__ */
+
+union scm_aligned_cell
+{
+  double alignment;
+  scm_t_cell cell;
+};
+
+typedef union scm_aligned_cell scm_t_aligned_cell;
+
+#endif /* !__GNUC__ */
+
+/* Make sure we get the right alignment.  */
+verify (alignof (scm_t_aligned_cell) >= 8);
 
 #endif  /* SCM__SCM_H */