Re: Bitshifts and "And" vs Floor-division and Modular

Discussion in 'Python' started by Mark Lawrence, Sep 7, 2012.

  1. On 07/09/2012 02:08, Cameron Simpson wrote:
    > On 07Sep2012 01:30, Mark Lawrence <> wrote:
    > | On 07/09/2012 01:01, jimbo1qaz wrote:
    > | > Is it faster to use bitshifts or floor division? And which is better, & or %?
    > | > All divisors and mods are power of 2, so are binary operations faster? And are they considered bad style?
    > |
    > | Why don't you use the timeit module and find out for yourself?
    > Because timeit doesn't output style advice?
    > Because timeit won't offer even a short single parapgraph description
    > of how python ints (even just in CPython) are implemented and how that
    > may affect performance in general?
    > To the OP: personally, I would suggest using % when I am thinking of
    > division and a bit shift when I am thinking of a bitshift, and only reach
    > for timeit when performance becomes an issue. Code for the algoritm,
    > and only optimise later.
    > Of course only a well run benchmark will measure the real world, but it
    > possible to address his other questions in a helpful fashion and address
    > the benchmark question in a less offputting tone. If you can't be
    > bothered, please don't. (Especially since these irritating posts from
    > you are usually in response to a post you feel could have used more
    > effort from the OP.)
    > Nobody answers all performance considerations or design choices with an
    > exhaustive timeit benchmark, and it is silly to suggest so. It is
    > helpful for people to have a mental model of the python internals
    > so they can make often-sensible choices from the start.
    > So try being helpful instead of slapping people down when they haven't
    > reached your private bar.
    > Cheers,

    I'm sorry but I refuse point blank to spoon feed, fit bibs and change
    nappies. I wouldn't do that on the tutor mailing list and I certainly
    wouldn't do it here. If any OP is too bone idle to do some research and
    then pose a sensible question relating to what they want to achieve,
    what they've done to achieve it and what issues they've got then I
    intend responding in the same way. Clearly your approach is different
    so we'll have to agree to disagree.


    Mark Lawrence.
    Mark Lawrence, Sep 7, 2012
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