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POpack bytes array with strange alignment requirements
 

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  1. POpack bytes array with strange alignment requirements
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    <p>Suppose you have 32 threads and 32 pieces of data for each thread to operate on independently, e.g.</p> <pre><code>struct data { unsigned short int N; char *features; //array length N uint *values; //array length N }; data alldata[32]; </code></pre> <p>Suppose that the shared memory for these threads is "partitioned" into 32 "banks", where each bank is 4 bytes wide. <strong>Each thread can read from its corresponding "bank" in parallel, but if threads try to access the same bank simlutaneously, the read operation serializes.</strong></p> <pre><code>bank | 0 | 1 | 2 | ..... bytes | 0 1 2 3 | 4 5 6 7 | 8 9 10 11 | .... bytes | 128 129 130 131 | 132 133 134 135 | 136 137 138 139 | ... ............... ............... threads | 0 | 1 | 2 | ..... </code></pre> <p>(This bizarre situation is called GPU computing).</p> <p>Thus, for maximum parallelization: (in terms of the picture above) the member variables of alldata[0] must only be written to the bytes in the first column. The member of variables of alldata[1] to the second column, etc. Equivalently,</p> <p>In other words, I must write the contents of <code>alldata[32]</code> into one dynamic array, where the member variables of <code>alldata[j]</code> are written in 4-byte intervals once every <code>32*4</code> bytes. Then, when I copy this dynamic array into the shared memory for the threads, it will be properly aligned for the banks.</p> <p><strong>Question:</strong> Does anybody know of any kind of package that will write variables to a byte array with proper spacing, as discussed above (once every <code>32*4</code> bytes) ?</p> <p>This is a desperation question...</p>
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    1. UScmo
    1. UScmo
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      1. VTUpMod
    1. COSo, does this all translate to "How do I align structs to 128 byte"?
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      1. USPlasmaHH
    2. CO@PlasmaHH No, because you need to alternate. e.g. write first four bytes of `alldata[0]` , then write first four bytes of `alldata[1]`, then first four bytes of `alldata[2]`, ....., the second four bytes of `alldata[0]`, then second four bytes of `alldata[1]`,.....
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      1. POpack bytes array with strange alignment requirements
      1. UScmo
    3. COWhat data type is `alldata[32]`?
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      1. POpack bytes array with strange alignment requirements
      1. USwallyk
 

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