box3x3(uniform float image[32][32], int x, int y) takes varying x and y
parameters and exploits parallelism coming from these vectors. For SSE4 it
will handle 4 pixels at a time. So you need to organise outer loops to
supply these pixels in chunks of 4 (or 8, or 16, depending on your target).
This loop will do the job:
for(uniform int ii = 0; ii < numRows; ii++){ // note uniform counter
for(int jj = 0; jj < numCols; jj++){ // note varying counter
mO[ii, jj] = box3x3(mI, jj, ii); // on the first iteration it will
handle pixels (0,0), (1,0), (2,0), (3,0), i.e. jj is (0,1,2,3), ii is
uniform int 0, which is casted to varying int (0,0,0,0).
}
}
In case of both counter are varying, it will basically handle only 4
diagonal points of out of 16 in 4x4 area: (0,0), (1,1), (2,2), (3,3).
On Fri, Aug 17, 2018 at 3:15 AM Royi <[email protected]> wrote:
> Hello,
>
> I'm trying to do my first steps with ISPC.
>
> I understand the concept of ISPC that you write the programs from the
> point of view of a single element.
> It is easy to understand in the case there is an array as input and array
> as output and the ISPC program is the whole program.
>
> What I don't get is how it the Box Blur example
> <https://ispc.github.io/ispc.html#uniform-control-flow> should be used by
> the host program.
>
> let's say we have an image (Single Channel) as mI.
> Should we iterate it like:
>
> for(ii = 0; ii < numRows; ii++){
> for(jj = 0; jj < numCols; jj++){
> mO[ii, jj] = box3x3(mI, jj, ii);
> }
> }
>
> But then it doesn't make sense.
> As it seem a "Gang" will update single value.
>
> Could someone show a simple example how to utilize ISPC for Image
> Filtering?
>
> Thank You.
>
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