linux-kernel - [PATCH v3 1/4] util_macros.h: add find

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Message-Id: <1426775420-31350-2-git-send-email-bgolaszewski@baylibre.com>
Date:	Thu, 19 Mar 2015 15:30:17 +0100
From:	Bartosz Golaszewski <bgolaszewski@...libre.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	lm-sensors <lm-sensors@...sensors.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <srostedt@...hat.com>,
	Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: [PATCH v3 1/4] util_macros.h: add find_closest() macro

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@...libre.com>
---
 include/linux/util_macros.h | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 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..f2097ce
--- /dev/null
+++ b/include/linux/util_macros.h
@@ -0,0 +1,39 @@
+#ifndef _LINUX_HELPER_MACROS_H_
+#define _LINUX_HELPER_MACROS_H_
+
+#define __find_closest(x, a, as, op)(					\
+{									\
+	typeof(as) _i, _as = (as) - 1;					\
+	typeof(x) _x = (x);						\
+	typeof(*a) *_a = (a);						\
+	for (_i = 0; _i < _as; _i++) {					\
+		if (_x op DIV_ROUND_CLOSEST(_a[_i] + _a[_i + 1], 2))	\
+			break;						\
+	}								\
+	(_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 get_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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