[thermal: thermal/next] fixp-arith: add a linear interpolation function

["thermal-bot for Craig Tatlor" <tip-bot2@linutronix.de>]

The following commit has been merged into the thermal/next branch of thermal:

Commit-ID:     8d502ef682fdbe0ddf2274dae903b07baf1140e0
Gitweb:        https://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux.git//8d502ef682fdbe0ddf2274dae903b07baf1140e0
Author:        Craig Tatlor <ctatlor97@gmail.com>
AuthorDate:    Fri, 04 Dec 2020 05:54:56 +03:00
Committer:     Jonathan Cameron <Jonathan.Cameron@huawei.com>
CommitterDate: Sat, 16 Jan 2021 18:14:53 

fixp-arith: add a linear interpolation function

Adds a function to interpolate against two points,
this is carried arount as a helper function by tons of drivers.

Signed-off-by: Craig Tatlor <ctatlor97@gmail.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20201204025509.1075506-3-dmitry.baryshkov@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 include/linux/fixp-arith.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/fixp-arith.h b/include/linux/fixp-arith.h
index 8396013..281cb4f 100644
--- a/include/linux/fixp-arith.h
+++ b/include/linux/fixp-arith.h
@@ -141,4 +141,23 @@ static inline s32 fixp_sin32_rad(u32 radians, u32 twopi)
 #define fixp_cos32_rad(rad, twopi)	\
 	fixp_sin32_rad(rad + twopi / 4, twopi)
 
+/**
+ * fixp_linear_interpolate() - interpolates a value from two known points
+ *
+ * @x0: x value of point 0
+ * @y0: y value of point 0
+ * @x1: x value of point 1
+ * @y1: y value of point 1
+ * @x: the linear interpolant
+ */
+static inline int fixp_linear_interpolate(int x0, int y0, int x1, int y1, int x)
+{
+	if (y0 == y1 || x == x0)
+		return y0;
+	if (x1 == x0 || x == x1)
+		return y1;
+
+	return y0 + ((y1 - y0) * (x - x0) / (x1 - x0));
+}
+
 #endif