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| Date | Tue, 4 Mar 2014 16:24:03 +1100 |
| Subject | Re: Reference |
| From | Chris Angelico <rosuav@gmail.com> |
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On Tue, Mar 4, 2014 at 3:52 PM, Steven D'Aprano <steve@pearwood.info> wrote: > This is why, unless performance is *really* critical, one should normally > write x*2 when multiplying x by 2 rather than x >> 1. (And in Python, the > overhead means that there is no real performance benefit to using bit > shifts instead of multiplication or division.) In most C compilers today (C being where x << 1 would be used rather than x * 2), the expressions would be equivalent, so you can still express it as x * 2 and let the compiler turn that into a bit shift. (And it's possible that "x * 5" will become "x << 2 + x", too.) Definitely go for the expressive version unless you've actually tested that the obscure version is faster. (Of course, that doesn't mean the bit-shift operators should never be used. If you're trying to pack three tiny integers into a single larger integer, you probably want bit shifts and bitwise or, not multiplication and addition, even though either would work.) Code should look like its intent. Warping it around performance is hardly ever worthwhile. ChrisA
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Reference "ast" <nomail@invalid.com> - 2014-03-03 10:42 +0100
Object identity (was: Reference) Ben Finney <ben+python@benfinney.id.au> - 2014-03-03 21:00 +1100
Re: Object identity (was: Reference) "ast" <nomail@invalid.com> - 2014-03-03 11:21 +0100
Re: Reference "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-03 05:09 -0800
Re: Reference Grant Edwards <invalid@invalid.invalid> - 2014-03-03 14:29 +0000
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-03 07:52 -0800
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 08:10 +1100
Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-03 15:24 -0600
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 08:31 +1100
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-03 21:35 +0000
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 00:07 +0200
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:18 +1100
Re: Reference Alister <alister.ware@ntlworld.com> - 2014-03-04 11:10 +0000
Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 11:48 +0000
Re: Reference "Rhodri James" <rhodri@wildebst.org.uk> - 2014-03-05 00:25 +0000
Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-03 15:51 -0600
Re: Reference Jerry Hill <malaclypse2@gmail.com> - 2014-03-03 17:02 -0500
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 00:22 +0200
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-04 09:27 +1100
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:33 +1100
Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 04:52 +0000
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-04 16:24 +1100
Re: Reference "Rhodri James" <rhodri@wildebst.org.uk> - 2014-03-05 01:08 +0000
Re: Reference Roy Smith <roy@panix.com> - 2014-03-04 21:09 -0500
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 19:36 -0800
Re: Reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-03-04 21:08 -0700
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 20:31 -0800
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 15:32 +1100
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 20:47 -0800
Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-05 05:06 +0000
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 21:47 -0800
Re: Reference alex23 <wuwei23@gmail.com> - 2014-03-05 16:01 +1000
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 22:10 -0800
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:22 +1100
Re: Reference alex23 <wuwei23@gmail.com> - 2014-03-05 16:28 +1000
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 12:24 +0000
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 12:21 +0000
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:20 +1100
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-05 09:40 -0800
Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-05 12:12 -0600
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 05:33 +1100
Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-05 18:19 +0000
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 22:23 +0200
Re: Reference Grant Edwards <invalid@invalid.invalid> - 2014-03-05 20:31 +0000
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 22:46 +0200
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:07 +1100
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:10 +1100
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 21:34 +0000
Re: Reference Terry Reedy <tjreedy@udel.edu> - 2014-03-05 18:00 -0500
Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-06 03:01 +0000
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 22:03 -0800
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:26 +1100
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 17:32 +1100
Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-05 08:24 -0600
Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-05 18:29 +0000
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 22:34 +0200
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:01 +1100
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 23:14 +0200
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-06 08:26 +1100
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 23:50 +0200
Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-06 00:35 +0000
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-06 11:50 +1100
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-06 17:46 +0000
Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-05 15:33 -0600
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:37 +1100
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-06 02:52 +0200
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 12:05 +1100
Re: Reference alex23 <wuwei23@gmail.com> - 2014-03-06 12:12 +1000
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 21:46 +0000
Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 08:23 +0200
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 22:33 -0800
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:40 +1100
Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 12:35 +0000
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 23:45 +1100
Re: Reference Jerry Hill <malaclypse2@gmail.com> - 2014-03-04 10:19 -0500
Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 15:42 +0000
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 03:02 +1100
Re: Reference Roy Smith <roy@panix.com> - 2014-03-04 11:14 -0500
Re: Reference MRAB <python@mrabarnett.plus.com> - 2014-03-04 17:12 +0000
Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 08:24 -0800
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 02:25 +1100
Re: Reference Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2014-03-05 14:37 +0100
Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 03:59 +0000
Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:17 +1100
Re: Reference Roy Smith <roy@panix.com> - 2014-03-03 18:02 -0500
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-04 10:09 +1100
Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 04:38 +0000
Re: Reference Terry Reedy <tjreedy@udel.edu> - 2014-03-03 13:48 -0500
Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 03:45 +0000
Re: Reference Alexander Blinne <news@blinne.net> - 2014-03-04 13:55 +0100
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 01:06 +1100
Re: Reference Alexander Blinne <news@blinne.net> - 2014-03-04 22:53 +0100
Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 09:01 +1100
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