[PATCH 1/3] r600: add span support for 2D tiling

[Conn Clark]

On Thu, May 27, 2010 at 8:51 AM, Brian Paul <brianp at vmware.com> wrote:
> Alex Deucher wrote:
>>
>> On Thu, May 27, 2010 at 10:55 AM, Matt Turner <mattst88 at gmail.com> wrote:
>>>>
>>>> +static inline GLint r600_log2(GLint n)
>>>> +{
>>>> +       GLint log2 = 0;
>>>> +
>>>> +       while (n >>= 1)
>>>> +               ++log2;
>>>> +       return log2;
>>>> +}
>>>
>>> Does mesa not provide something like this?
>>
>> The only one I could find was a gallium utility function.
>
> There's a logbase2() function in teximage.c but it might not be equivalent.
>
> -Brian
>
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This code could be written with a faster algorithm requiring  just 13 operations

+               pixel_number |= ((x >> 0) & 1) << 0; // pn[0] = x[0]
+               pixel_number |= ((y >> 0) & 1) << 1; // pn[1] = y[0]
+               pixel_number |= ((x >> 1) & 1) << 2; // pn[2] = x[1]
+               pixel_number |= ((y >> 1) & 1) << 3; // pn[3] = y[1]
+               pixel_number |= ((x >> 2) & 1) << 4; // pn[4] = x[2]
+               pixel_number |= ((y >> 2) & 1) << 5; // pn[5] = y[2]



/* suitable for all 16 bit or greater processors that can do an
unsigned 16 bit or greater multiply */
/*  tested and verified  */

pixel_number = ((((x & 0x07) * 0x1111 & 0x8421) * 0x1249 >> 9) & 0x55 ) |
                             ((((y & 0x07) * 0x1111 & 0x8421) * 0x1249
>> 8) & 0xAA );

Note if it is known that x and y are less than or equal to 7 it can be
done in 11 operations.

Cheers

Conn
-- 

Conn O. Clark

Observation: In formal computer science advances are made
by standing on the shoulders of giants. Linux has proved
that if there are enough of you, you can advance just as
far by stepping on each others toes.