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Raw numerical data physical memory addresses aligning

Asked by Igor Varfolomeev on 10 Oct 2015
Latest activity Edited by Jan
on 18 Oct 2015
I'm currently writing c++ mex function. I'd like to utilize some SIMD instructions.
  1. Is it safe to assume, that the pointer to the raw numeric data (the result on mxGetData() ) is aligned ?
  2. Is it 16-byte (SSE-like) or 32-byte (AVX-like) alignment?
  3. Does it depend on the CPU capabilities, Matlab version or anything else?
  4. Is there any document about this subject?
Matlab makes some use of SSE as well, so, most probably, each array must be aligned. And my initial experiments do confirm, that all raw-data pointers are 32-byte aligned... But it would be nice to have an "official confirmation" and/or notices about the possible caveats.

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1 Answer

Answer by Jan
on 10 Oct 2015
Edited by Jan
on 18 Oct 2015

Since at least R2008b I've never observed an array, which is not aligned at 16 bytes. My Mex functions stop with an error otherwise and no user reported such an error yet. This concerns 32 and 64 bit versions of Matlab and Windows.
I agree that an official statement is required.
[EDITED] "Aligned at 32 bits" -> "Aligned at 16 bytes"
I've used SSE statements only, so I did not check for 32 byte alignment.

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Thanks for the answer! It greatly increases my belief, that everything should be OK.
Though, you probably mean "aligned at 32 bytes", don't you ? :)

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