Arbitrary interleaver (shuffle) using IPP

Arbitrary interleaver (shuffle) using IPP

I read somewhere that the new processors include special instructions for small lookup tables.  Is there a way to optimize the following simple operation:

float data[10] = {0, ...9}

unsigned int idx[10] = {2,3,5,0,...9} // Arbitrary permutation of 0..9

float result[10];

result = data[idx]

I have to do this operation often and it takes quite a bit of time in a 'for' loop. Currently
for (int i=0;i<10;i++) result[i]=data[idx[i]];



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Have yiou checked to see if your compiler has the auto-vectorizer turned on? That will probably help you a lot. Since there are only 10 elements in the loop the overhead of threading the function may make the performance worse.

The 10 element array was just an example. Actual arrays may have 1000 elements. I believe icpc will auto-vectorize when /O3 switch is used.

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