doxygen, make constant time for real.

lib/roken/ct.c

@@ -35,6 +35,23 @@
 
 #include <sys/types.h>
 
+/**
+ * Constant time compare to memory regions. The reason for making it
+ * constant time is to make sure that timeing information leak from
+ * where in the function the diffrence is.
+ *
+ * ct_memcmp() can't be used to order memory regions like memcmp(),
+ * for example, use ct_memcmp() with qsort().
+ *
+ * @param p1 memory region 1 to compare
+ * @param p2 memory region 2 to compare
+ * @param len length of memory
+ *
+ * @return 0 when the memory regions are equal, non zero if not
+ *
+ * @ingroup roken
+ */
+
 int
 ct_memcmp(const void *p1, const void *p2, size_t len)
 {
@@ -43,7 +60,6 @@ ct_memcmp(const void *p1, const void *p2, size_t len)
     int r = 0;
 
     for (i = 0; i < len; i++)
-	if (s1[i] != s2[i] && r == 0)
-	    r = s1[i] - s2[i];
-    return r;
+	r |= (s1[i] ^ s2[i]);
+    return !!r;
 }