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Re: Loop optimisation.

From The Natural Philosopher <tnp@invalid.invalid>
Newsgroups comp.lang.javascript
Subject Re: Loop optimisation.
Date 2021-04-11 11:36 +0100
Organization A little, after lunch
Message-ID <s4ujfh$h3l$3@dont-email.me> (permalink)
References <s4snvd$cr0$1@dont-email.me> <86e3bc08-8877-45ce-9881-519d0a41b9c0n@googlegroups.com>

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On 11/04/2021 06:22, Michael Haufe (TNO) wrote:
> On Saturday, April 10, 2021 at 12:41:08 PM UTC-5, The Natural Philosopher wrote:
>> Does Js do it?
>>
>> I have some close to real time audio processing code and I want it to
>> run floating point on a raspberry Pi - no FP coprocessors so no wasted
>> cycles required.
>>
>> The question is - in C if you do something like
>>
>> function (int x)
>> for(somecondition)
>> if (x greater than whatever)
>> extra blah;
>> else completely different blah;
>> endfor
>>
>> will one hopes result in two completely different loops being
>> established so that conditionl is actually evaluated outside the loop -
>> i.e
>>
>> function (int x)
>> if (x greater than whatever)
>> for(somecondition)
>> extra blah;
>> endfor
>> else
>> for(somecondition)
>> completely different blah;
>> endfor
>> endif
>>
>> is what a decent compiler optimised for speed might well do.
>>
>> Does javascript though?
> 
> Modern JavaScript engines use JIT compilation. Depending on what you are doing it can be faster than the equivalent C code. A couple examples:
> 
> <https://www.reddit.com/r/javascript/comments/bnnrnt/javascript_faster_than_c_to_execute_mathematical/>
> <https://gist.github.com/spion/3049314>
> 
> If you want more details on why that's the case here is one description among many:
> 
> <https://hacks.mozilla.org/2017/02/a-crash-course-in-just-in-time-jit-compilers/>
> 
> So you may think you're using floats, but in reality it may have converted those to int32 or smaller as well as inlined and compiled to machine code a significant portion of your script.
> 
>> And of course Javascript makes all numbers floating point...so the
>> comparison will be cycle hungry comparing two floats
> 
> No, it doesn't. JavaScript has more than just floats and the JIT will find opportunities to utilize smaller number types behind the scenes where possible and appropriate.
> 

That is useful information, thanks.
It seems that 'test and try' is the optimal approach.

So far its no issues at all on Intel hardware as far as I have developed 
it, or android on an ARM ...


-- 
Microsoft : the best reason to go to Linux that ever existed.

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Thread

Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-10 18:41 +0100
  Re: Loop optimisation. John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-10 19:14 +0100
    Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-11 11:33 +0100
      Re: Loop optimisation. John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-11 15:03 +0100
        Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-11 07:38 -0700
          Re: Loop optimisation. Jonas Thörnvall <jonas.thornvall@gmail.com> - 2021-04-11 13:36 -0700
          Re: Loop optimisation. John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-12 18:05 +0100
            Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-12 23:16 +0100
              Re: Loop optimisation. Jonas Thörnvall <jonas.thornvall@gmail.com> - 2021-04-13 05:19 -0700
                Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-13 06:21 -0700
        Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-12 01:36 +0100
          Re: Loop optimisation. John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-12 18:04 +0100
            Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-12 23:09 +0100
              Re: Loop optimisation. John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-13 20:08 +0100
                Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-13 21:41 +0100
                Re: Loop optimisation. John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-14 18:24 +0100
  Re: Loop optimisation. Kristjan Robam <he12457@hotmail.com> - 2021-04-10 13:36 -0700
    Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-11 11:34 +0100
  Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-10 22:22 -0700
    Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-11 11:36 +0100
    Re: Loop optimisation. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-14 02:20 +0200
      Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-14 06:48 -0700
        Re: Loop optimisation. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-14 17:31 +0200
          Re: Loop optimisation. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-14 18:00 +0200
            Re: Loop optimisation. The Natural Philosopher <tnp@invalid.invalid> - 2021-04-14 19:25 +0100
            Re: Loop optimisation. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-14 23:10 +0200
              Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-17 09:45 -0700
            Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-17 09:43 -0700
              Re: Loop optimisation. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-17 21:45 +0200
                Re: Loop optimisation. Scott Sauyet <scott.sauyet@gmail.com> - 2021-04-18 19:06 -0700
          Re: Loop optimisation. "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-04-17 08:50 -0700

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