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Re: 100 Things

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From Ian Collins <ian-news@hotmail.com>
Newsgroups comp.lang.misc
Subject Re: 100 Things
Date Thu, 01 May 2014 11:03:31 +1200
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BartC wrote:
> "Kaz Kylheku" <kaz@kylheku.com> wrote:
>>
>> Since strlen is a standard C function, the compiler can know that it has
>> no side effects, and that it can be hoisted out of the loop if the loop
>> doesn't alter the variable s, and doesn't potentially modify any memory
>> that could be inside s.
>
> But in the absence of optimisation, or if the compiler can't determine what
> happens to s, the expectation seems to be that the terminating expression is
> calculated repeatedly.
>
> That's what I used to do, but now I calculate any such expression just once,
> whether it can change or not. That's a slightly saner way of doing things as
> the maximum loop iterations are known in advance. (That probably suits a
> simpler iteration statement better than C's more open-ended one.)
>
> (It also gives the compiler I'm working on now its first performance edge
> over gcc:

Comparing performance without optimisation (or regards to correctness!) 
is pointless.

-- 
Ian Collins

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Thread

C: 100 Things "BartC" <bc@freeuk.com> - 2014-04-29 17:57 +0100
  Re: 100 Things "James Harris" <james.harris.1@gmail.com> - 2014-04-30 07:40 +0100
    Re: 100 Things "BartC" <bc@freeuk.com> - 2014-04-30 12:16 +0100
      Re: 100 Things "James Harris" <james.harris.1@gmail.com> - 2014-04-30 13:54 +0100
        Re: 100 Things "BartC" <bc@freeuk.com> - 2014-04-30 14:39 +0100
          Re: 100 Things "James Harris" <james.harris.1@gmail.com> - 2014-04-30 20:18 +0100
            Re: 100 Things "BartC" <bc@freeuk.com> - 2014-04-30 22:40 +0100
              Re: 100 Things Kaz Kylheku <kaz@kylheku.com> - 2014-04-30 22:09 +0000
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-04-30 23:36 +0100
                Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-01 11:03 +1200
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 09:47 +0100
              Re: 100 Things "James Harris" <james.harris.1@gmail.com> - 2014-05-01 00:35 +0100
                Re: 100 Things Andy Walker <news@cuboid.co.uk> - 2014-05-01 11:03 +0100
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 20:16 +0100
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 12:44 +0100
                Re: 100 Things "James Harris" <james.harris.1@gmail.com> - 2014-05-02 11:11 +0100
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-02 13:32 +0100
                Re: 100 Things "James Harris" <james.harris.1@gmail.com> - 2014-05-02 16:42 +0100
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-02 17:54 +0100
          Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-01 11:01 +1200
      Re: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-04-30 21:13 -0400
        Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 09:26 +0100
          Re: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-01 16:08 -0400
      Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-01 13:42 +1200
        Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 09:35 +0100
          Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-01 21:02 +1200
            Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 10:40 +0100
              Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-01 22:06 +1200
          Re: 100 Things "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-01 11:08 +0200
            Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 11:02 +0100
              Re: 100 Things "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-01 13:57 +0200
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 15:12 +0100
                Re: 100 Things "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-01 17:18 +0200
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 17:04 +0100
                Re: 100 Things Kaz Kylheku <kaz@kylheku.com> - 2014-05-01 18:30 +0000
                Re: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-01 16:08 -0400
                Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-02 08:30 +1200
                Re: 100 Things George Neuner <gneuner2@comcast.net> - 2014-05-03 01:29 -0400
                Re: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-03 02:37 -0400
                Re: 100 Things George Neuner <gneuner2@comcast.net> - 2014-05-03 15:39 -0400
                Re: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-03 17:30 -0400
                Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-04 20:05 +1200
                Re: 100 Things George Neuner <gneuner2@comcast.net> - 2014-05-04 13:28 -0400
                Re: 100 Things Ian Collins <ian-news@hotmail.com> - 2014-05-05 07:40 +1200
                Re: 100 Things "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-01 22:00 +0200
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-01 23:24 +0100
                Re: 100 Things "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-02 08:59 +0200
                Re: 100 Things "BartC" <bc@freeuk.com> - 2014-05-02 09:53 +0100
                Re: 100 Things "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2014-05-02 11:22 +0200
                Re: 100 Things Kaz Kylheku <kaz@kylheku.com> - 2014-05-01 18:26 +0000
                Re: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-01 16:08 -0400
                Re: 100 Things Kaz Kylheku <kaz@kylheku.com> - 2014-05-02 02:49 +0000
  Re: C: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-04-30 22:08 -0400
  Re: C: 100 Things "BartC" <bc@freeuk.com> - 2014-07-25 23:53 +0100
    Re: C: 100 Things "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-07-26 05:38 -0400
      Re: C: 100 Things "BartC" <bc@freeuk.com> - 2014-07-26 13:51 +0100
        Re: C: 100 Things rick.c.hodgin@gmail.com - 2014-10-25 04:48 -0700
  Re: C: 100 Things "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2014-10-25 04:50 -0700

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