ALIGNOF() helper

diff --git a/alignof/_info.c b/alignof/_info.c
new file mode 100644 (file)
index 0000000..b5afa02
--- /dev/null
+++ b/alignof/_info.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <string.h>
+#include "config.h"
+
+/**
+ * alignof - ALIGNOF() macro to determine alignment of a type.
+ *
+ * Many platforms have requirements that certain types must be aligned
+ * to certain address boundaries, such as ints needing to be on 4-byte
+ * boundaries.  Attempting to access variables with incorrect
+ * alignment may cause performance loss or even program failure (eg. a
+ * bus signal).
+ *
+ * There are times which it's useful to be able to programatically
+ * access these requirements, such as for dynamic allocators.
+ *
+ * Example:
+ *     #include <stdio.h>
+ *     #include "alignof/alignoff.h"
+ *
+ *     int main(int argc, char *argv[])
+ *     {
+ *             char arr[sizeof(int)];
+ *
+ *             if ((unsigned long)arr % ALIGNOF(int)) {
+ *                     printf("arr %p CANNOT hold an int\n", arr);
+ *                     exit(1);
+ *             } else {
+ *                     printf("arr %p CAN hold an int\n", arr);
+ *                     exit(0);
+ *             }
+ *     }
+ */
+int main(int argc, char *argv[])
+{
+       if (argc != 2)
+               return 1;
+
+       if (strcmp(argv[1], "depends") == 0) {
+               printf("build_assert\n");
+               return 0;
+       }
+
+       return 1;
+}

diff --git a/alignof/alignof.h b/alignof/alignof.h
new file mode 100644 (file)
index 0000000..d146e4c
--- /dev/null
+++ b/alignof/alignof.h
@@ -0,0 +1,19 @@
+#ifndef CCAN_ALIGNOF_H
+#define CCAN_ALIGNOF_H
+#include "config.h"
+
+/**
+ * ALIGNOF - get the alignment of a type
+ * @t: the type to test
+ *
+ * This returns a safe alignment for the given type.
+ */
+#if HAVE_ALIGNOF
+/* A GCC extension. */
+#define ALIGNOF(t) __alignof__(t)
+#else
+/* Alignment by measuring structure padding. */
+#define ALIGNOF(t) ((char *)(&((struct { char c; t _h; } *)0)->_h) - (char *)0)
+#endif
+
+#endif /* CCAN_ALIGNOF_H */

diff --git a/alignof/test/run.c b/alignof/test/run.c
new file mode 100644 (file)
index 0000000..f76fb66
--- /dev/null
+++ b/alignof/test/run.c
@@ -0,0 +1,62 @@
+#include <stdlib.h>
+#include <stddef.h>
+#include <tap/tap.h>
+#include "alignof/alignof.h"
+
+/* Alignment is remarkably difficult to test.  The rules may be more
+ * complex than ALIGNOF() can know: eg. on i386 __alignof__(double) == 8, but
+ * __alignof__(struct containing double) == 4.
+ *
+ * Technically, we can only test that we give *at least* the alignment which
+ * naturally occurs, and that accesses work.
+ *
+ * For the moment, we work around double. */
+struct lots_of_types
+{
+       char c;
+       short s;
+       char c2;
+       int i;
+       char c3;
+       float f;
+       char c4;
+       double d;
+       char c5;
+};
+
+int main(int argc, char *argv[])
+{
+       struct lots_of_types lots_of_types, *lp = malloc(sizeof(*lp));
+       char c;
+       short s;
+       char c2;
+       int i;
+       char c3;
+       float f;
+       char c4;
+       double d;
+
+       /* Make sure we use all the variables. */
+       c = 0;
+       c2 = c3 = c4 = c;
+
+       plan_tests(15);
+       ok1((unsigned long)&c % ALIGNOF(char) == 0);
+       ok1((unsigned long)&s % ALIGNOF(short) == 0);
+       ok1((unsigned long)&i % ALIGNOF(int) == 0);
+       ok1((unsigned long)&f % ALIGNOF(float) == 0);
+       ok1((unsigned long)&d % ALIGNOF(double) == 0);
+
+       ok1((unsigned long)&lots_of_types.c % ALIGNOF(char) == 0);
+       ok1((unsigned long)&lots_of_types.s % ALIGNOF(short) == 0);
+       ok1((unsigned long)&lots_of_types.i % ALIGNOF(int) == 0);
+       ok1((unsigned long)&lots_of_types.f % ALIGNOF(float) == 0);
+       ok1(offsetof(struct lots_of_types, d) % ALIGNOF(double) == 0);
+
+       ok1((unsigned long)&lp->c % ALIGNOF(char) == 0);
+       ok1((unsigned long)&lp->s % ALIGNOF(short) == 0);
+       ok1((unsigned long)&lp->i % ALIGNOF(int) == 0);
+       ok1((unsigned long)&lp->f % ALIGNOF(float) == 0);
+       ok1((unsigned long)&lp->d % ALIGNOF(double) == 0);
+       exit(exit_status());
+}