SIMD array append idiom

[mcmc...@gmail.com]

I have a case where I want to write something like this:

uniform int* uniform array = ...;

uniform int offset = 0;

foreach(x = ...) {

    if ( should_append(x) ) {

        array[offset++] = x;

    }

}

... but of course, that doesn't compile. 

Is there an idiom for doing this in ISPC?  It seems like it would be possible with some combination of broadcast()-like operations but I can't quite put my finger on it (and maybe it's simply just not practical).

I'm thinking of something like:

foreach(x = ...) {

    if ( should_append(x) ) {

        int varying_offset = some_incrementing_magic(offset);

        array[varying_offset] = x;

    }

}

... where each lane computes its own (unique) array offset based on the results of the gang.

Thanks in advance,

Mike

[Dmitry Babokin]

Mike,

I'm not sure that I understand your question correctly. Are you trying to pick some lanes of varying computations (i.e. based on should_append(x) selector) and serialize them in an array?

If so, you probably need this: https://ispc.github.io/ispc.html#packed-load-and-store-operations

Dmitry.

PS It's preferred to post questions on https://github.com/ispc/ispc/discussions - it has wider reach and more chances to get answered.

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[mcmc...@gmail.com]

That looks like exactly what I am looking for.  I've scanned that document several times and somehow overlooked that section.   Thanks!