[libcamera-devel] [PATCH 1/2] libipa: Round gain code before returning the value

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-11-19 10:25:58)
> We can have the case where the gain is very close to 1, as coded in
> double, and after gainCode() returns, the value as an uint32_t is 0. In
> order to avoid that, always round the value halfway cases away from zero
> before returning.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>

This seems to make sense.

Are there any issues with other values being rounded? I presume not.
Is there any requirement to further protect or warn if gainCode is
returned as zero? or can that still be valid in some situations?


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
> index 0b0eb503..67cf6913 100644
> --- a/src/ipa/libipa/camera_sensor_helper.cpp
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -7,6 +7,8 @@
>   */
>  #include "camera_sensor_helper.h"
>  
> +#include <cmath>
> +
>  #include <libcamera/base/log.h>
>  
>  /**
> @@ -61,8 +63,8 @@ uint32_t CameraSensorHelper::gainCode(double gain) const
>         ASSERT(analogueGainConstants_.m0 == 0 || analogueGainConstants_.m1 == 0);
>         ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>  
> -       return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> -              (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
> +       return std::round((analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +                         (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0));
>  }
>  
>  /**
> -- 
> 2.32.0
>