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  • gideony2
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    Classic case of slowdown due to global rounding mode is
    int=float;
    the rules say you chop, and on the 80×87 this forces rounding mode to change twice, which costs a few
    dozen cycles; see http://stereopsis.com/FPU.html.

    There is a special optimization https://docs.microsoft.com/en-us/cpp/build/reference/qifist-suppress-ftol?view=vs-2017 to avoid this double change and allow rounding.

    • This reply was modified 4 years, 1 month ago by  gideony2.
  • gideony2
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    Post count: 9

    It may make sense at very low precision (way below IEEE). See https://arxiv.org/pdf/1502.02551v1.pdf

  • gideony2
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    Post count: 9
    in reply to: Russian CPU Elbrus #2979

    Russian web-page (accessed just now; pointer in Wikipedia), last line:
    Ожидаемый год завершения работы: 2015

    which translates as
    Expected Completion Year 2015

  • gideony2
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    Post count: 9
    in reply to: Specification #1865

    Is C200x the proposed Unix time standard?

  • gideony2
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    Post count: 9

    The A5/1 cipher should be as cheap as 3 small LFSRs

  • gideony2
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    Post count: 9

    (1) decent crypto is just plain cheap; and: does an LFSR _have_ a middle? (if all bits were shifted 17 bits around, it would be just as good an LFSR)

    I don’t know how to think about pseudo-random (it is supposed to look random, unless you play “unfairly”); I do know how to think about crypto: if the key is secret, distinguishing the output from random is _VERY_ expensive.

    (2) without randomized rounding, 1+0.1+0.1+0.1+0.1 …. (all the way across 100 pages; rounded to integer) will still be 1. Randomized, it will be 0.1*(# of adds), +- epsilon.

  • gideony2
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    Post count: 9

    If you go for stochastic rounding, make sure the random numbers are decent (some are not — see https://en.wikipedia.org/wiki/RANDU ).

    Simplest fix: stream cipher with exportable key-length (or: encrypt 0,1,2… under a block-cipher — also exportable, if jail-time is an issue)

  • gideony2
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    Post count: 9
    in reply to: Prediction #1854

    In an embedded system, with code in ROM, how can the prediction table get back into the load module?

  • gideony2
    Participant
    Post count: 9

    Microsoft calls /QIfist an optimization, so I call it one.

    Kahan: “Optimization is replacing something that works by something that almost works &is cheaper”

    There is enough horsepower in /QIfist that MS implements &publishes this “optimization”.

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