[PATCH 3/3] libipa: camera_sensor_helper: Fix rounding of gainCode

[Kieran Bingham]

The implementation of gainCode for both Exponential and Linear gain
models does not generate a gainCode that matches the result of the
reverse operation.

This can be seen by converting sequential gainCodes to a gain
and converting that back to the gainCode. The values do not
translate back due to rounding errors.

Correct the rounding error and ensure that gainCode translation
produces accurate bi-directional conversions from the perspective
of the gainCode.

This fixes the IMX290, IMX296, IMX327 and IMX335 which use the
Exponential gain model helpers, as well as IMX219 IMX258 and IMX477
which use the Linear gain model helpers.

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---
 src/ipa/libipa/camera_sensor_helper.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
index a925b37b9f7c..39e10d86a2c7 100644
--- a/src/ipa/libipa/camera_sensor_helper.cpp
+++ b/src/ipa/libipa/camera_sensor_helper.cpp
@@ -64,13 +64,13 @@ uint32_t CameraSensorHelper::gainCode(double gain) const
 	case AnalogueGainLinear:
 		ASSERT(k.linear.m0 == 0 || k.linear.m1 == 0);
 
-		return (k.linear.c0 - k.linear.c1 * gain) /
-		       (k.linear.m1 * gain - k.linear.m0);
+		return std::round((k.linear.c0 - k.linear.c1 * gain) /
+				  (k.linear.m1 * gain - k.linear.m0));
 
 	case AnalogueGainExponential:
 		ASSERT(k.exp.a != 0 && k.exp.m != 0);
 
-		return std::log2(gain / k.exp.a) / k.exp.m;
+		return std::round(std::log2(gain / k.exp.a) / k.exp.m);
 
 	default:
 		ASSERT(false);
-- 
2.34.1