Loading ...
Sorry, an error occurred while loading the content.

Re: [jslint] Re: Save and restore jslint settings

Expand Messages
  • Paul Novitski
    ... At 9/2/2009 10:24 AM, aseem.kishore@ymail.com wrote: ... Christian, my guess is that the reasoning behind your comment is an assumption that Aseem would
    Message 1 of 13 , Sep 2, 2009
    • 0 Attachment
      >--- In jslint_com@yahoogroups.com, "christian.wirkus"
      ><christian.wirkus@...> wrote:
      > > Are you sure bitwise operators optimize anything in Javascript?
      > > Javascript isn't C, and the data type number is 64 bit float, not integer.

      At 9/2/2009 10:24 AM, aseem.kishore@... wrote:
      ...
      >I'm also not sure about whether that indeed optimizes anything. I
      >haven't done profiling comparisons; I'm just reusing well-known algorithms.



      Christian, my guess is that the reasoning behind your comment is an
      assumption that Aseem would choose bit-manipulation primarily to
      optimize the code on a low level. From Aseem's reply that doesn't
      appear to be the case. He's using algorithms because they're
      dependable and do the job without regard for how they work on a low
      level, and that's interesting.

      I offer the opinion that, unless a particular language structure
      occurs in a loop that iterates an enormous number of times, low-level
      optimization is irrelevant compared to the importance of its
      usability in the high-level script.

      (Can we get away with calling usability high-level or human-level
      optimization?)

      If a bit of syntax is easy to use, read, proofread, and modify, then
      it wins. The whole purpose of high-level scripts such as JavaScript
      is their human benefit only; the computers don't care, they would run
      binary machine code much more quickly. But these days the chips are
      so bloody fast that it takes a lot of inefficiency to make their
      round trips perceptible to our own slow-poke bags of brain jelly.

      Regards,

      Paul
      __________________________

      Paul Novitski
      Juniper Webcraft Ltd.
      http://juniperwebcraft.com
    • pauanyu
      ... I had the same idea, but with different syntax: use strict ; var prop, foo; /*options forin: true */ for (prop in foo) { foo[prop] = foo ; } /*end
      Message 2 of 13 , Sep 2, 2009
      • 0 Attachment
        --- In jslint_com@yahoogroups.com, "woomla" <woomla@...> wrote:
        >
        > Every know and then I want to change a /*jslint*/ setting for a particular statement. After the statement I want to restore the setting to its previous state. It would be nice if I can restore the setting without knowing its previous state/value (i.e. indent).
        >
        > A solution would be something to push the options and afterwards pop the options:
        >
        > "use strict";
        > var prop, foo;
        >
        > /*pushoptions*/
        > /*jslint forin:true*/
        > for (prop in foo) {
        > foo[prop] = "foo";
        > }
        > /*jslint forin:false*/
        > /*popoptions*/
        >
        >
        > I've implemented this in my pspad plugin and it works great. I would love to see it in the official script though.
        >

        I had the same idea, but with different syntax:

        "use strict";
        var prop, foo;

        /*options forin: true */
        for (prop in foo) {
        foo[prop] = "foo";
        }
        /*end options */
      • christian.wirkus
        Sure. Write what is understood best. That s what code quality is about, I think. I just wanted to mention that bitwise operators in Javascript are not as
        Message 3 of 13 , Sep 3, 2009
        • 0 Attachment
          Sure. Write what is understood best. That's what code quality is about, I think.
          I just wanted to mention that bitwise operators in Javascript are not as efficient as in other languages (because I read bitwise and optimized so close to one another). And often are used for gaining performance only.
          And I thought of something like this:
          var x = 2;
          x * 2 === x << 1;

          If there is a context where bitwise is a clear and short solution to a problem, use it.

          Christian


          --- In jslint_com@yahoogroups.com, Paul Novitski <paul@...> wrote:
          >
          >
          > >--- In jslint_com@yahoogroups.com, "christian.wirkus"
          > ><christian.wirkus@> wrote:
          > > > Are you sure bitwise operators optimize anything in Javascript?
          > > > Javascript isn't C, and the data type number is 64 bit float, not integer.
          >
          > At 9/2/2009 10:24 AM, aseem.kishore@... wrote:
          > ...
          > >I'm also not sure about whether that indeed optimizes anything. I
          > >haven't done profiling comparisons; I'm just reusing well-known algorithms.
          >
          >
          >
          > Christian, my guess is that the reasoning behind your comment is an
          > assumption that Aseem would choose bit-manipulation primarily to
          > optimize the code on a low level. From Aseem's reply that doesn't
          > appear to be the case. He's using algorithms because they're
          > dependable and do the job without regard for how they work on a low
          > level, and that's interesting.
          >
          > I offer the opinion that, unless a particular language structure
          > occurs in a loop that iterates an enormous number of times, low-level
          > optimization is irrelevant compared to the importance of its
          > usability in the high-level script.
          >
          > (Can we get away with calling usability high-level or human-level
          > optimization?)
          >
          > If a bit of syntax is easy to use, read, proofread, and modify, then
          > it wins. The whole purpose of high-level scripts such as JavaScript
          > is their human benefit only; the computers don't care, they would run
          > binary machine code much more quickly. But these days the chips are
          > so bloody fast that it takes a lot of inefficiency to make their
          > round trips perceptible to our own slow-poke bags of brain jelly.
          >
          > Regards,
          >
          > Paul
          > __________________________
          >
          > Paul Novitski
          > Juniper Webcraft Ltd.
          > http://juniperwebcraft.com
          >
        • aseem.kishore@ymail.com
          For what it s worth, some of the code I write does indeed run in a tight loop many times (striving for 60 frames/sec), and low-level optimizations have proven
          Message 4 of 13 , Sep 4, 2009
          • 0 Attachment
            For what it's worth, some of the code I write does indeed run in a tight loop many times (striving for 60 frames/sec), and low-level optimizations have proven to help (especially in IE).

            For curiosity's sake, I did some testing between bit-shifting and regular math, and it seems bit-shifting is in fact faster for the cases I use.

            Using these two functions, with i going from 0 to 50000:

            function pow2BitShifting(i) {
            var x = 1 << (i % 30);
            }

            function pow2RegularMath(i) {
            var x = Math.pow(2, (i % 30));
            }

            In Firefox:

            Powers of 2 w/ bit shifting: 38 msecs
            Powers of 2 w/ regular math: 69 msecs

            In IE:

            Powers of 2 w/ bit shifting: 56 msecs
            Powers of 2 w/ regular math: 107 msecs

            In Chrome and Safari (nearly identical here):

            Powers of 2 w/ bit shifting: 2 msecs (!!)
            Powers of 2 w/ regular math: 16 msecs

            So anyway, it's clear that using bitwise operators has its place, so to get back to the original topic, it would be great if I could opt-in on a per-function basis. =)

            Aseem

            --- In jslint_com@yahoogroups.com, "christian.wirkus" <christian.wirkus@...> wrote:
            >
            > Sure. Write what is understood best. That's what code quality is about, I think.
            > I just wanted to mention that bitwise operators in Javascript are not as efficient as in other languages (because I read bitwise and optimized so close to one another). And often are used for gaining performance only.
            > And I thought of something like this:
            > var x = 2;
            > x * 2 === x << 1;
            >
            > If there is a context where bitwise is a clear and short solution to a problem, use it.
            >
            > Christian
            >
            >
            > --- In jslint_com@yahoogroups.com, Paul Novitski <paul@> wrote:
            > >
            > >
            > > >--- In jslint_com@yahoogroups.com, "christian.wirkus"
            > > ><christian.wirkus@> wrote:
            > > > > Are you sure bitwise operators optimize anything in Javascript?
            > > > > Javascript isn't C, and the data type number is 64 bit float, not integer.
            > >
            > > At 9/2/2009 10:24 AM, aseem.kishore@ wrote:
            > > ...
            > > >I'm also not sure about whether that indeed optimizes anything. I
            > > >haven't done profiling comparisons; I'm just reusing well-known algorithms.
            > >
            > >
            > >
            > > Christian, my guess is that the reasoning behind your comment is an
            > > assumption that Aseem would choose bit-manipulation primarily to
            > > optimize the code on a low level. From Aseem's reply that doesn't
            > > appear to be the case. He's using algorithms because they're
            > > dependable and do the job without regard for how they work on a low
            > > level, and that's interesting.
            > >
            > > I offer the opinion that, unless a particular language structure
            > > occurs in a loop that iterates an enormous number of times, low-level
            > > optimization is irrelevant compared to the importance of its
            > > usability in the high-level script.
            > >
            > > (Can we get away with calling usability high-level or human-level
            > > optimization?)
            > >
            > > If a bit of syntax is easy to use, read, proofread, and modify, then
            > > it wins. The whole purpose of high-level scripts such as JavaScript
            > > is their human benefit only; the computers don't care, they would run
            > > binary machine code much more quickly. But these days the chips are
            > > so bloody fast that it takes a lot of inefficiency to make their
            > > round trips perceptible to our own slow-poke bags of brain jelly.
            > >
            > > Regards,
            > >
            > > Paul
            > > __________________________
            > >
            > > Paul Novitski
            > > Juniper Webcraft Ltd.
            > > http://juniperwebcraft.com
            > >
            >
          • Stefan Weiss
            ... That s not really a fair comparison. The second function has to do a lookup for Math , find its pow property, and execute a method call to Math.pow. So
            Message 5 of 13 , Sep 4, 2009
            • 0 Attachment
              On 04/09/09 18:10, aseem.kishore@... wrote:
              > For curiosity's sake, I did some testing between bit-shifting and
              > regular math, and it seems bit-shifting is in fact faster for the
              > cases I use.
              >
              > Using these two functions, with i going from 0 to 50000:
              >
              > function pow2BitShifting(i) {
              > var x = 1 << (i % 30);
              > }
              >
              > function pow2RegularMath(i) {
              > var x = Math.pow(2, (i % 30));
              > }

              That's not really a fair comparison. The second function has to do a
              lookup for 'Math', find its 'pow' property, and execute a method call to
              Math.pow.

              So yes, in this case, bit shifting is faster than a call to Math.pow
              with base 2, but that doesn't prove that the bit operations themselves
              are handled efficiently in JS.


              cheers,
              stefan
            • Aseem Kishore
              Fair enough. If you can think of a better way to test this, let me know. I m all for finding a more efficient alternative. =) Aseem ... [Non-text portions of
              Message 6 of 13 , Sep 4, 2009
              • 0 Attachment
                Fair enough. If you can think of a better way to test this, let me know. I'm
                all for finding a more efficient alternative. =)
                Aseem

                On Fri, Sep 4, 2009 at 9:36 AM, Stefan Weiss <weiss@...> wrote:

                >
                >
                > On 04/09/09 18:10, aseem.kishore@... <aseem.kishore%40ymail.com>wrote:
                > > For curiosity's sake, I did some testing between bit-shifting and
                > > regular math, and it seems bit-shifting is in fact faster for the
                > > cases I use.
                > >
                > > Using these two functions, with i going from 0 to 50000:
                > >
                > > function pow2BitShifting(i) {
                > > var x = 1 << (i % 30);
                > > }
                > >
                > > function pow2RegularMath(i) {
                > > var x = Math.pow(2, (i % 30));
                > > }
                >
                > That's not really a fair comparison. The second function has to do a
                > lookup for 'Math', find its 'pow' property, and execute a method call to
                > Math.pow.
                >
                > So yes, in this case, bit shifting is faster than a call to Math.pow
                > with base 2, but that doesn't prove that the bit operations themselves
                > are handled efficiently in JS.
                >
                > cheers,
                > stefan
                >
                >


                [Non-text portions of this message have been removed]
              • aseem.kishore@ymail.com
                ... Fair point. Since that s my use case, it s a valid comparison for my scenario (even if I cache a local reference to Math.pow first, the numbers are almost
                Message 7 of 13 , Sep 4, 2009
                • 0 Attachment
                  --- In jslint_com@yahoogroups.com, Stefan Weiss <weiss@...> wrote:
                  >
                  > On 04/09/09 18:10, aseem.kishore@... wrote:
                  > > For curiosity's sake, I did some testing between bit-shifting and
                  > > regular math, and it seems bit-shifting is in fact faster for the
                  > > cases I use.
                  > >
                  > > Using these two functions, with i going from 0 to 50000:
                  > >
                  > > function pow2BitShifting(i) {
                  > > var x = 1 << (i % 30);
                  > > }
                  > >
                  > > function pow2RegularMath(i) {
                  > > var x = Math.pow(2, (i % 30));
                  > > }
                  >
                  > That's not really a fair comparison. The second function has to do a
                  > lookup for 'Math', find its 'pow' property, and execute a method call to
                  > Math.pow.
                  >
                  > So yes, in this case, bit shifting is faster than a call to Math.pow
                  > with base 2, but that doesn't prove that the bit operations themselves
                  > are handled efficiently in JS.
                  >
                  >
                  > cheers,
                  > stefan
                  >

                  Fair point. Since that's my use case, it's a valid comparison for my scenario (even if I cache a local reference to Math.pow first, the numbers are almost identical, so apparently the bottleneck isn't the lookups).

                  But to make a more fair comparison for the purposes of the underlying question, I changed the test to this:

                  function times2BitShifting(i) {
                  var x = i << 1;
                  }

                  function times2RegularMath(i) {
                  var x = 2 * i;
                  }

                  Again, i goes from 0 to 50000. Across all browsers, the two take essentially the same amount of time. I sometimes just get a 1 ms difference in favor of bit-shifting.

                  Doubling w/ bit-shifting: 31
                  Doubling w/ regular math: 32

                  So is this a fair enough comparison? Using bitwise operators seems to have no performance penalty, and in cases where it's actually useful (e.g. powers of 2), it's significantly [in a statistical sense] faster than regular math.

                  Aseem
                • Arthur Blake
                  One would think that modern JIT compiler implementations of JS would make this whole discussion moot... On Fri, Sep 4, 2009 at 4:01 PM,
                  Message 8 of 13 , Sep 4, 2009
                  • 0 Attachment
                    One would think that modern JIT compiler implementations of JS would
                    make this whole discussion moot...

                    On Fri, Sep 4, 2009 at 4:01 PM,
                    aseem.kishore@...<aseem.kishore@...> wrote:
                    >
                    >
                    > --- In jslint_com@yahoogroups.com, Stefan Weiss <weiss@...> wrote:
                    >
                    >>
                    >> On 04/09/09 18:10, aseem.kishore@... wrote:
                    >> > For curiosity's sake, I did some testing between bit-shifting and
                    >> > regular math, and it seems bit-shifting is in fact faster for the
                    >> > cases I use.
                    >> >
                    >> > Using these two functions, with i going from 0 to 50000:
                    >> >
                    >> > function pow2BitShifting(i) {
                    >> > var x = 1 << (i % 30);
                    >> > }
                    >> >
                    >> > function pow2RegularMath(i) {
                    >> > var x = Math.pow(2, (i % 30));
                    >> > }
                    >>
                    >> That's not really a fair comparison. The second function has to do a
                    >> lookup for 'Math', find its 'pow' property, and execute a method call to
                    >> Math.pow.
                    >>
                    >> So yes, in this case, bit shifting is faster than a call to Math.pow
                    >> with base 2, but that doesn't prove that the bit operations themselves
                    >> are handled efficiently in JS.
                    >>
                    >>
                    >> cheers,
                    >> stefan
                    >>
                    >
                    > Fair point. Since that's my use case, it's a valid comparison for my
                    > scenario (even if I cache a local reference to Math.pow first, the numbers
                    > are almost identical, so apparently the bottleneck isn't the lookups).
                    >
                    > But to make a more fair comparison for the purposes of the underlying
                    > question, I changed the test to this:
                    >
                    > function times2BitShifting(i) {
                    > var x = i << 1;
                    > }
                    >
                    > function times2RegularMath(i) {
                    > var x = 2 * i;
                    > }
                    >
                    > Again, i goes from 0 to 50000. Across all browsers, the two take essentially
                    > the same amount of time. I sometimes just get a 1 ms difference in favor of
                    > bit-shifting.
                    >
                    > Doubling w/ bit-shifting: 31
                    > Doubling w/ regular math: 32
                    >
                    > So is this a fair enough comparison? Using bitwise operators seems to have
                    > no performance penalty, and in cases where it's actually useful (e.g. powers
                    > of 2), it's significantly [in a statistical sense] faster than regular math.
                    >
                    > Aseem
                    >
                    >
                  • Stefan Weiss
                    ... Much better, thank you. I didn t have the time to cook up a test myself earlier, and this pretty much confirms what I expected. ... I wasn t expecting to
                    Message 9 of 13 , Sep 4, 2009
                    • 0 Attachment
                      On 04/09/09 22:01, aseem.kishore@... wrote:
                      > --- In jslint_com@yahoogroups.com, Stefan Weiss <weiss@...> wrote:
                      >> That's not really a fair comparison. The second function has to do a
                      >> lookup for 'Math', find its 'pow' property, and execute a method call to
                      >> Math.pow.
                      >>
                      >> So yes, in this case, bit shifting is faster than a call to Math.pow
                      >> with base 2, but that doesn't prove that the bit operations themselves
                      >> are handled efficiently in JS.
                      >
                      > Fair point. Since that's my use case, it's a valid comparison for my
                      > scenario (even if I cache a local reference to Math.pow first, the
                      > numbers are almost identical, so apparently the bottleneck isn't the
                      > lookups).
                      >
                      > But to make a more fair comparison for the purposes of the underlying
                      > question, I changed the test to this:
                      >
                      > function times2BitShifting(i) {
                      > var x = i << 1;
                      > }
                      >
                      > function times2RegularMath(i) {
                      > var x = 2 * i;
                      > }
                      >
                      > Again, i goes from 0 to 50000. Across all browsers, the two take
                      > essentially the same amount of time. I sometimes just get a 1 ms
                      > difference in favor of bit-shifting.
                      >
                      > Doubling w/ bit-shifting: 31
                      > Doubling w/ regular math: 32
                      >
                      > So is this a fair enough comparison?

                      Much better, thank you. I didn't have the time to cook up a test myself
                      earlier, and this pretty much confirms what I expected.

                      > Using bitwise operators seems to have no performance penalty, and in
                      > cases where it's actually useful (e.g. powers of 2), it's significantly
                      > [in a statistical sense] faster than regular math.

                      I wasn't expecting to see a performance penalty. My point is that
                      JavaScript isn't C, and micro-optimizations using bit shifts won't bring
                      any real advantage over normal arithmetic operations. (They're not very
                      helpful in C anymore either, because modern compilers are all about
                      optimization, and can do this sort of thing in their sleep.) It won't
                      make much of a difference whether you write "i << 10" or "i * 1024".

                      In your specific case, the performance gain is real, and apparently it's
                      mostly due to avoiding the method call (unless you wrap the bit shifting
                      it in a function, of course).

                      When I'm not in a tight loop, I tend to go for the most readable
                      implementation, even if it means using objects and properties instead of
                      bit fields.


                      cheers,
                      stefan
                    Your message has been successfully submitted and would be delivered to recipients shortly.