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Re: Should [[ -v 1 ]] be supported?


From: Peng Yu
Subject: Re: Should [[ -v 1 ]] be supported?
Date: Thu, 27 Dec 2018 19:47:08 -0600

On Thu, Dec 27, 2018 at 7:37 PM G. Branden Robinson
<address@hidden> wrote:
>
> At 2018-12-27T18:39:26-0600, Peng Yu wrote:
> > What I meant in my original email is that I want something for testing
> > if there is a command line argument (one or more, the exact number
> > does not matter). $# gives more than that info, because it tells not
> > only whether is any command line argument, but also how many. This
> > could lead to slower performance if the goal is to just test if there
> > is an argument.
>
> You should look into how integer comparisons are done in hardware.
>
> For instance, comparison and subtraction operations are often comparable
> (or even identical) in cycle count because they both perform a
> subtraction "under the hood".  You need to be programming in assembly
> language to influence execution at such depths.
>
> See, e.g.,
>
> https://www.quora.com/What-is-the-difference-between-cmp-and-sub-instruction-in-8086microprocessor
>
> As others have noted, if you are worried about marginal performance
> impacts this small, margin you are probably writing in the wrong
> language, or distracting yourself with tiny details when you do not even
> know the cyclomatic complexity of your code or the big-O classification
> of your algorithms.
>
> Attack those problems first, and see what you discover.

The problem is that bash is not systematically profiled for
performance at all. I am doing it step it by step. There are many more
that I have already tested. You can not dismiss this one just because
it may not have a large impact.

-- 
Regards,
Peng



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