# [Pixman] [PATCH 13/15] pixman-filter: refactor cubic polynominal and don't range check

Oded Gabbay oded.gabbay at gmail.com
Tue Dec 22 04:38:05 PST 2015

```On Sat, Dec 12, 2015 at 8:06 PM,  <spitzak at gmail.com> wrote:
> From: Bill Spitzak <spitzak at gmail.com>
>
> The other filters do not check for x being in range, so there is
> no reason for cubic to do so.

This argument is a bit problematic.
We could also argue that this filter was actually implemented
correctly/more robust and we should add checks for x to the other
filters.

I fail to see how this saves us much except from removing a condition
in a very specific path.

Do you argue that ax will never ever be >=2 ?

Oded

> ---
>  pixman/pixman-filter.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
> index 7e10108..bf9dce3 100644
> --- a/pixman/pixman-filter.c
> +++ b/pixman/pixman-filter.c
> @@ -109,18 +109,16 @@ general_cubic (double x, double B, double C)
>
>      if (ax < 1)
>      {
> -       return ((12 - 9 * B - 6 * C) * ax * ax * ax +
> -               (-18 + 12 * B + 6 * C) * ax * ax + (6 - 2 * B)) / 6;
> -    }
> -    else if (ax >= 1 && ax < 2)
> -    {
> -       return ((-B - 6 * C) * ax * ax * ax +
> -               (6 * B + 30 * C) * ax * ax + (-12 * B - 48 * C) *
> -               ax + (8 * B + 24 * C)) / 6;
> +       return (((12 - 9 * B - 6 * C) * ax +
> +                (-18 + 12 * B + 6 * C)) * ax * ax +
> +               (6 - 2 * B)) / 6;
>      }
>      else
>      {
> -       return 0;
> +       return ((((-B - 6 * C) * ax +
> +                (6 * B + 30 * C)) * ax +
> +               (-12 * B - 48 * C)) * ax +
> +               (8 * B + 24 * C)) / 6;
>      }
>  }
>
> --
> 1.9.1
>
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```