[PATCH v8 06/10] math.h: Add macros for rounding to closest value

[Devarsh Thakkar]

Add below rounding related macros:

round_closest_up(x, y) : Rounds x to closest multiple of y where y is a
power of 2, with a preference to round up in case two nearest values are
possible.

round_closest_down(x, y) : Rounds x to closest multiple of y where y is a
power of 2, with a preference to round down in case two nearest values are
possible.

roundclosest(x, y) : Rounds x to closest multiple of y, this macro should
generally be used only when y is not multiple of 2 as otherwise
round_closest* macros should be used which are much faster.

Examples:
 * round_closest_up(17, 4) = 16
 * round_closest_up(15, 4) = 16
 * round_closest_up(14, 4) = 16
 * round_closest_down(17, 4) = 16
 * round_closest_down(15, 4) = 16
 * round_closest_down(14, 4) = 12
 * roundclosest(21, 5) = 20
 * roundclosest(19, 5) = 20
 * roundclosest(17, 5) = 15

Signed-off-by: Devarsh Thakkar <devarsht@xxxxxx>
---
NOTE: This patch is inspired from the Mentor Graphics IPU driver [1]
which uses similar macro locally and which is updated in further patch
in the series to use this generic macro instead along with other drivers
having similar requirements.

[1]:
https://elixir.bootlin.com/linux/v6.8.9/source/drivers/gpu/ipu-v3/ipu-image-convert.c#L480

V8:
- Add new macro to round to nearest value for non-multiple of 2
- Update commit message as suggested

V1->V6 (No change, patch introduced in V7)
---
 include/linux/math.h | 65 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/include/linux/math.h b/include/linux/math.h
index dd4152711de7..e2cc3769ed0e 100644
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -34,6 +34,54 @@
  */
 #define round_down(x, y) ((x) & ~__round_mask(x, y))
 
+/**
+ * round_closest_up - round closest to be multiple of specified value (which is
+ *                    power of 2) with preference to rounding up
+
+ * @x: the value to round
+ * @y: multiple to round closest to (must be a power of 2)
+ *
+ * Rounds @x to closest multiple of @y (which must be a power of 2).
+ * The value can be either rounded up or rounded down depending upon rounded
+ * value's closeness to the specified value. If there are two closest possible
+ * values, i.e. the difference between the specified value and it's rounded up
+ * and rounded down values is same then preference is given to rounded up
+ * value.
+ *
+ * To perform arbitrary rounding to closest value (not multiple of 2), use
+ * roundclosest().
+ *
+ * Examples :
+ * round_closest_up(17, 4) = 16
+ * round_closest_up(15, 4) = 16
+ * round_closest_up(14, 4) = 16
+ */
+#define round_closest_up(x, y) round_down((x) + (y) / 2, (y))
+
+/**
+ * round_closest_down - round closest to be multiple of specified value (which
+ *			is power of 2) with preference to rounding down
+ *
+ * @x: the value to round
+ * @y: multiple to round closest to (must be a power of 2)
+ *
+ * Rounds @x to closest multiple of @y (which must be a power of 2).
+ * The value can be either rounded up or rounded down depending upon rounded
+ * value's closeness to the specified value. If there are two closest possible
+ * values, i.e. the difference between the specified value and it's rounded up
+ * and rounded down values is same then preference is given to rounded up
+ * value.
+ *
+ * To perform arbitrary rounding to closest value (not multiple of 2), use
+ * roundclosest().
+ *
+ * Examples :
+ * round_closest_down(17, 4) = 16
+ * round_closest_down(15, 4) = 16
+ * round_closest_down(14, 4) = 12
+ */
+#define round_closest_down(x, y) round_up((x) - (y) / 2, (y))
+
 #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP
 
 #define DIV_ROUND_DOWN_ULL(ll, d) \
@@ -77,6 +125,23 @@
 }							\
 )
 
+/**
+ * roundclosest - round to nearest multiple
+ * @x: the value to round
+ * @y: multiple to round nearest to
+ *
+ * Rounds @x to nearest multiple of @y.
+ * The rounded value can be greater than or less than @x depending
+ * upon it's nearness to @x. If @y will always be a power of 2, consider
+ * using the faster round_closest_up() or round_closest_down().
+ *
+ * Examples :
+ * roundclosest(21, 5) = 20
+ * roundclosest(19, 5) = 20
+ * roundclosest(17, 5) = 15
+ */
+#define roundclosest(x, y) rounddown((x) + (y) / 2, (y))
+
 /*
  * Divide positive or negative dividend by positive or negative divisor
  * and round to closest integer. Result is undefined for negative
-- 
2.39.1