include: add BSD rounding macros to sys/param.h

These macros are commonly provided on BSD systems. They are not part of
C nor POSIX but these types of operations can be required in drivers
implementation as well as in user space. The operations themself are
simple but kind of cryptic when placed in the code as is. Thus having
macro with an appropriate name is beneficial.

The use of BSD naming here is only to cling to at least some other
implementation instead of creating completelly NuttX specific one.

Kudos to @hartmannathan for the source code documentation.

Signed-off-by: Karel Kočí <kkoci@elektroline.cz>

include/sys/param.h

@@ -53,6 +53,51 @@
 #  define nitems(_a)    (sizeof(_a) / sizeof(0[(_a)]))
 #endif /* nitems */
 
+/* Macros for counting and rounding.
+ *
+ * These macros accept value to be rounded or checked as 'a' and base as 'b'.
+ * They are consistent with those provided by some BSDs.
+ *
+ * howmany() calculates how many b fit into a.
+ *
+ * rounddown() and roundup() round a to the next b.
+ *
+ * rounddown2() and roundup2() are for powers of 2 only.
+ *
+ * powerof2() returns 1 if a is a power of 2, 0 otherwise.
+ *
+ * Warning: rounddown2() and roundup2() can be used only if b is power of 2,
+ * otherwise they will produce wrong result.
+ *
+ * In all of these macros, outcome is undefined if b is 0.
+ *
+ * All parameters are assumed to be unsigned integers.
+ */
+
+#ifndef howmany
+#  define howmany(a, b)	(((a) + ((b) - 1)) / (b))
+#endif /* howmany */
+
+#ifndef rounddown
+#  define	rounddown(a, b)	(((a) / (b)) * (b))
+#endif /* rounddown */
+
+#ifndef rounddown2
+#  define	rounddown2(a, b) ((a) & ~((b) - 1))
+#endif /* rounddown2 */
+
+#ifndef roundup
+#  define	roundup(a, b)	((((a) + ((b) - 1)) / (b)) * (b))
+#endif /* roundup */
+
+#ifndef roundup2
+#  define	roundup2(a, b)	(((a) + ((b) - 1)) & ~((b) - 1))
+#endif /* roundup2 */
+
+#ifndef powerof2
+#  define powerof2(a)	(!(((a) - 1) & (a)))
+#endif /* powerof2 */
+
 /****************************************************************************
  * Public Type Definitions
  ****************************************************************************/