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  • Pourya_ShirazianNovember 10, 2011 12:57 PM PST   
    Rotate shift in AVX and SSE
    I need to shift values in a simd register and replace from left or right. Basically I have an array like {4,5,4,5} in SSE or {4,5,4,5,4,5,4,5} in AVX and need to convert them to {5,4,5,4} or {5,4,5,4,5,4,5,4}. I need the solution to work with both SSE and AVX instruction sets.


    Pourya Shirazian

    sirridaNovember 10, 2011 10:39 PM PST
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    		 #1
    Rotate shift in AVX and SSE
    Do you mean data dependent rotation (i.e. different rotation of each subword) or a cyclically exchange of the subwords.
    A solution of the first problem is sketched on my site or with AVX2 (Intel proposal: 2 times VPSLLV* or VPSRLV* and one POR) or XOP (AMD Bulldozer: VPROT*) commands.
    The second problem is easily solved by the commands SHUFPS, SHUFPD, PSHUFD, PSHUFB and PALIGNR; unfortunately these commands are somewhat limited for YMM usage because of their missing cross-lane operations.

    More at http://programming.sirrida.de

    jimdempseyatthecoveNovember 12, 2011 1:27 PM PST
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    		 #2
    Rotate shift in AVX and SSE
    I need to shift values in a simd register and replace from left or right. Basically I have an array like {4,5,4,5} in SSE or {4,5,4,5,4,5,4,5} in AVX and need to convert them to {5,4,5,4} or {5,4,5,4,5,4,5,4}. I need the solution to work with both SSE and AVX instruction sets.

     
    If I take you literally that the only numbers are:

    {4,5,4,5} in SSE or {4,5,4,5,4,5,4,5} in AVX, then pxor with
    {1,1,1,1} in SSE or {1,1,1,1,1,1,1,1} in AVX, to convert to
    {5,4,5,4} in SSE or  {5,4,5,4,5,4,5,4} in AVX.

    xor again with same number sequence to convert back from
    {5,4,5,4} in SSE or  {5,4,5,4,5,4,5,4} in AVX to
    {4,5,4,5} in SSE or {4,5,4,5,4,5,4,5} in AVX.

    Jim Dempsey



    Blog: The Parallel Void
    www.quickthreadprogramming.com

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