[Pixman] [PATCH v11 09/14] pixman-filter: Nested polynomial for cubic

[Bill Spitzak]

On 02/07/2016 04:57 AM, Oded Gabbay wrote:
> On Fri, Feb 5, 2016 at 9:49 AM,  <spitzak at gmail.com> wrote:
>> From: Bill Spitzak <spitzak at gmail.com>
>>
>> v11: Restored range checks
>>
>> Signed-off-by: Bill Spitzak <spitzak at gmail.com>
>> ---
>>   pixman/pixman-filter.c | 14 ++++++++------
>>   1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
>> index e82871f..e5ef8e6 100644
>> --- a/pixman/pixman-filter.c
>> +++ b/pixman/pixman-filter.c
>> @@ -109,14 +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;
>> +       return (((12 - 9 * B - 6 * C) * ax +
>> +                (-18 + 12 * B + 6 * C)) * ax * ax +
>> +               (6 - 2 * B)) / 6;
>>       }
>> -    else if (ax >= 1 && ax < 2)
>> +    else if (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 ((((-B - 6 * C) * ax +
>> +                 (6 * B + 30 * C)) * ax +
>> +                (-12 * B - 48 * C)) * ax +
>> +               (8 * B + 24 * C)) / 6;
>>       }
>>       else
>>       {
>> --
>> 1.9.1
>>
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>
> I'm sorry, I was probably not clear enough in my response for the v10
> patch. In my response then, I also referred to the fact you removed
> the special case of handling ax >= 2. I meant that I also didn't see
> the benefit of removing that check.
>
> Oded

This version does not remove the range check. I just kept the nested 
version of the polynomial (I have heard but not personally confirmed 
that some compilers will not do this optimization). This one also 
removes the redundant ax >= 1 because that is true if the previous if 
statement is false.