Groups > comp.lang.java.programmer > #7259

Re: Using Enumerated Types as Array Indexes

Newsgroups	comp.lang.java.programmer
From	Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at>
Subject	Re: Using Enumerated Types as Array Indexes
References	(10 earlier) <j2hhnj$4js$1@dont-email.me> <j2hr70$qiq$1@dont-email.me> <9b72b5FrgfU1@mid.individual.net> <slrnj4tgh1.6gl.avl@gamma.logic.tuwien.ac.at> <9b85ssF8vsU1@mid.individual.net>
Message-ID	<slrnj4trd9.6gl.avl@gamma.logic.tuwien.ac.at> (permalink)
Date	2011-08-19 23:11 +0000

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Robert Klemme <shortcutter@googlemail.com> wrote:
> On 19.08.2011 22:05, Andreas Leitgeb wrote:
>> Robert Klemme<shortcutter@googlemail.com>  wrote:
>>> All solutions to fix remainder into modulo but keep the wrap around
>>> which have been proposed so far share a common disadvantage: if the
>>> number range is not a multiple of the divisor the value distribution
>>> will not be uniform.
>>>
>>> The solution I used to fix this employed a do while loop and
>>> compareAndSet() to reset the value to the beginning of the range (0 in
>>> this case) in a thread safe manner.
>>
>> There's a much simpler "meta-way" to fix it:  just stick to powers of
>> 2 for the array length - then the overflow *does* always happen at a
>> multiple of the divisor and the value distribution uniform :-)
>
> I reckon you do not mean that suggestion serious.  Just in case: 
> limiting to powers of 2 was not an option here.  And if it was, I would 
> not have used modulo or AtomicInteger's features but just used binary & 
> to cut off leading bits.

Of course I don't know the wider context, but to me it seemed as if 
a power-of-2 sized array would be such a natural choice, that you'd
surely use one, anyway, already. Under these circumstances, (n % N)
would have seemed to be the same as (n & (N-1)), yet shorter and
clearer - except, as then learned, for negative n ...

May I ask, what other entity imposes the array length on you, and why
choosing the next larger power of 2 will not do?

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Using Enumerated Types as Array Indexes KevinSimonson <kvnsmnsn@hotmail.com> - 2011-08-16 07:53 -0700
  Re: Using Enumerated Types as Array Indexes Patricia Shanahan <pats@acm.org> - 2011-08-16 09:30 -0700
  Re: Using Enumerated Types as Array Indexes Tom Anderson <twic@urchin.earth.li> - 2011-08-16 21:37 +0100
  Re: Using Enumerated Types as Array Indexes Gene Wirchenko <genew@ocis.net> - 2011-08-16 14:54 -0700
    Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-16 20:47 -0400
  Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-16 20:38 -0400
    Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-16 17:52 -0700
      Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-16 21:56 -0400
        Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-16 20:20 -0700
          Re: Using Enumerated Types as Array Indexes Lew <lewbloch@gmail.com> - 2011-08-16 20:45 -0700
            Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-17 06:31 -0300
              Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-17 13:28 +0000
                Re: Using Enumerated Types as Array Indexes Lew <lewbloch@gmail.com> - 2011-08-17 07:17 -0700
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-17 19:02 +0200
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-17 16:09 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-17 23:48 +0000
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-17 17:34 -0700
                Re: Using Enumerated Types as Array Indexes Patricia Shanahan <pats@acm.org> - 2011-08-17 18:07 -0700
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-18 08:22 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-18 18:37 +0000
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-18 11:50 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-18 20:49 +0000
                Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-18 14:48 -0700
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-18 22:50 +0000
                Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:49 -0400
                Re: Using Enumerated Types as Array Indexes Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-08-17 21:50 -0400
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-19 14:13 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 20:05 +0000
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 00:20 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 23:11 +0000
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 11:21 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-20 11:45 +0000
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 15:23 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-20 16:15 +0000
                Re: Using Enumerated Types as Array Indexes Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-08-17 21:34 -0400
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-18 07:58 +0200
                Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-18 06:29 -0300
                Re: Using Enumerated Types as Array Indexes RedGrittyBrick <RedGrittyBrick@spamweary.invalid> - 2011-08-18 10:47 +0100
                Re: Using Enumerated Types as Array Indexes Lew <lewbloch@gmail.com> - 2011-08-18 11:35 -0700
                Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-18 18:30 -0300
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-19 14:57 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 20:10 +0000
                Re: Using Enumerated Types as Array Indexes Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-08-19 19:12 -0300
                Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-20 00:26 +0200
                Re: Using Enumerated Types as Array Indexes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-08-19 22:59 +0000
          Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:34 -0400
            Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:46 -0400
              Re: Using Enumerated Types as Array Indexes markspace <-@.> - 2011-08-17 19:51 -0700
    Re: Using Enumerated Types as Array Indexes David Lamb <dalamb@cs.queensu.ca> - 2011-08-17 08:29 -0400
      Re: Using Enumerated Types as Array Indexes Robert Klemme <shortcutter@googlemail.com> - 2011-08-17 16:04 +0200
      Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:51 -0400
  Re: Using Enumerated Types as Array Indexes Niklas Holsti <niklas.holsti@tidorum.invalid> - 2011-08-17 11:24 +0300
    Re: Using Enumerated Types as Array Indexes Arne Vajhøj <arne@vajhoej.dk> - 2011-08-17 21:55 -0400
      Re: Using Enumerated Types as Array Indexes Niklas Holsti <niklas.holsti@tidorum.invalid> - 2011-08-18 10:59 +0300
  Re: Using Enumerated Types as Array Indexes Roedy Green <see_website@mindprod.com.invalid> - 2011-08-17 22:09 -0700

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