How to change Floating Point Control Word (FPCW) in MATLAB?

I am using the MATLAB COM interface for OpenDSS, where OpenDSS uses 80-bit floating-point values. more detailes in the discussion: https://sourceforge.net/p/electricdss/discussion/861976/thread/d3d147ec/#c3a2

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Answer 2

Fred 2015-9-4

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https://ww2.mathworks.cn/matlabcentral/answers/239512-how-to-change-floating-point-control-word-fpcw-in-matlab#answer_191283

I have seen the link but I could not quite get what should I do, and also the thing they are doing it in C but I'm using pure Matlab, I need something more like for normal MATLAB users.

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Walter Roberson 2015-9-4

You will need to be specific about which operating system you are using and which possibilities you want the user to be able to select.

The documentation that I am scanning indicates that the FPCW handles only the x87 FPU calculations, and that these days a lot of calculations are done in SSE and SSE2 instructions which use a different control register http://developer.amd.com/community/blog/2009/07/06/ieee-floating-point-exception-handling-in-windows-os/ . MATLAB calls into highly optimized libraries for larger calculations, and those optimized libraries are likely to be using SSE* or whatever post-x87 they can leverage because x87 performance is not scalable. If you adjust the FPCW you run into the possibility that the output behavior you see will depend upon the size of your data in ways that are not intuitive, with "small" calculations being affected (because they might run on x87) and "big" calculations not being affected (because they run on higher performance architectures, possibly even GPUs.)