[PATCH v4 1/5] util_macros.h: add find_closest() macro

[Bartosz Golaszewski]

Searching for the member of an array closest to 'x' is
duplicated in several places.

Add a new include - util_macros.h - and two macros that
implement this algorithm for arrays sorted both in ascending
and descending order.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
---
 include/linux/util_macros.h | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 include/linux/util_macros.h

diff --git a/include/linux/util_macros.h b/include/linux/util_macros.h
new file mode 100644
index 0000000..d5f4fb6
--- /dev/null
+++ b/include/linux/util_macros.h
@@ -0,0 +1,40 @@
+#ifndef _LINUX_HELPER_MACROS_H_
+#define _LINUX_HELPER_MACROS_H_
+
+#define __find_closest(x, a, as, op)					\
+({									\
+	typeof(as) __fc_i, __fc_as = (as) - 1;				\
+	typeof(x) __fc_x = (x);						\
+	typeof(*a) *__fc_a = (a);					\
+	for (__fc_i = 0; __fc_i < __fc_as; __fc_i++) {			\
+		if (__fc_x op DIV_ROUND_CLOSEST(__fc_a[__fc_i] +	\
+						__fc_a[__fc_i + 1], 2))	\
+			break;						\
+	}								\
+	(__fc_i);							\
+})
+
+/**
+ * find_closest - locate the closest element in a sorted array
+ * @x: The reference value.
+ * @a: The array in which to look for the closest element. Must be sorted
+ *  in ascending order.
+ * @as: Size of 'a'.
+ *
+ * Returns the index of the element closest to 'x'.
+ */
+#define find_closest(x, a, as) __find_closest(x, a, as, <=)
+
+/**
+ * find_closest_descending - locate the closest element in a sorted array
+ * @x: The reference value.
+ * @a: The array in which to look for the closest element. Must be sorted
+ *  in descending order.
+ * @as: Size of 'a'.
+ *
+ * Similar to find_closest() but 'a' is expected to be sorted in descending
+ * order.
+ */
+#define find_closest_descending(x, a, as) __find_closest(x, a, as, >=)
+
+#endif
-- 
2.1.4

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