Re: Challenge for Feeb: dealing with large numbers in C

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: Challenge for Feeb: dealing with large numbers in C
Date	2019-10-28 22:07 +0100
Organization	A noiseless patient Spider
Message-ID	<qp7lbf$onf$1@dont-email.me> (permalink)
References	(17 earlier) <87y2x5r47n.fsf@bsb.me.uk> <LCztF.910712$aq7.468058@fx09.am4> <87o8y0rcq2.fsf@bsb.me.uk> <qp7fmc$k0m$1@dont-email.me> <87imo8r56n.fsf@bsb.me.uk>

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On 28/10/2019 21:22, Ben Bacarisse wrote:
> David Brown <david.brown@hesbynett.no> writes:
> 
>> On 28/10/2019 18:39, Ben Bacarisse wrote:
>>> Bart <bc@freeuk.com> writes:
>>>
>>>> On 28/10/2019 02:31, Ben Bacarisse wrote:
>>>>> Bart <bc@freeuk.com> writes:
>>>>
>>>>>
>>>>>> Interpreted bubble-sort sorts 5000 numbers in about 1 second, while
>>>>>> the above insertion sort does it in 0.4 seconds, with the differences
>>>>>> narrowing rapidly for smaller data. But my qsort (still interpreted)
>>>>>> can sort nearly 1000000 numbers in 1 second.
>>>>>
>>>>> It would be interesting to see what that comes down to if you switch to
>>>>> insertion sort for small partitions.
>>>>
>>>> Not much as it turns out. Sorting a 1M-element array of random
>>>> integers goes from 0.8 to 0.78 seconds [this excludes array generation
>>>> time], if using my insertion sort for partitions of 10 or fewer
>>>> elements.
>>>
>>> Thanks.  Like so many things to do with timing, this might be one of
>>> those that has been dramatically altered by modern memory architectures.
>>> And it obviously depends on the exact code.
>>>
>>
>> I remember reading a paper about this, suggesting that the "big O" in
>> operation count is a poor indicator of performance on modern systems,
>> and that the most important factor is minimising cache thrashing.
> 
> What an odd remark.  Asymptotic bounds on operation counts were never a
> good indicator of performance.  Do you remember anything more that could
> identify the author?
> 

Big O operation counts is often taken as an indication of performance 
scaling (to be more accurate than my first remark).  In terms of 
operation counts alone, an O(n.log n) algorithm will be faster than an 
O(n²) algorithm for big enough n.  It is not uncommon for people to 
taken into account the scaling of memory space too.  But the point of 
the paper's author is that cache usage - the hit and miss rates - can 
easily be more important than the operations that are usually counted 
(typically compares and swaps, for a sorting algorithm).

I suppose cache effects won't change the asymptotic behaviour, since you 
can only have a cache miss in combination with an operation, but it can 
be very significant when comparing algorithms with the same asymptotic 
operation counts, or when working with data sets that are not /that/ big.

Thread

Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-20 18:12 -0400
  Re: Challenge for Feeb: dealing with large numbers in C Barry Schwarz <schwarzb@delq.com> - 2019-10-20 18:33 -0700
    Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-20 23:16 -0400
      Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-21 13:15 +0100
        Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 14:40 -0400
          Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-22 00:54 +0100
            Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-22 10:05 +0200
            Re: Challenge for Feeb: dealing with large numbers in C Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-23 07:18 -0700
          Re: Challenge for Feeb: dealing with large numbers in C Manfred <noname@invalid.add> - 2019-10-26 20:01 +0200
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-26 17:50 -0400
              Re: Challenge for Feeb: dealing with large numbers in C Manfred <noname@add.invalid> - 2019-10-28 16:33 +0100
      Re: Challenge for Feeb: dealing with large numbers in C Barry Schwarz <schwarzb@delq.com> - 2019-10-21 07:56 -0700
      Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 16:46 +0100
        Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 14:57 -0400
          Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 20:53 +0100
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 16:05 -0400
              Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 21:12 +0100
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 20:08 -0400
              Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-22 10:27 +0200
          Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-22 19:45 +0100
            Re: Challenge for Feeb: dealing with large numbers in C Eli the Bearded <*@eli.users.panix.com> - 2019-10-22 19:58 +0000
            Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-23 11:46 -0400
              Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-23 20:02 +0100
              Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 01:38 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-23 22:10 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ike Naar <ike@sdf.lonestar.org> - 2019-10-24 07:24 +0000
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 09:29 -0400
                Re: Challenge for Feeb: dealing with large numbers in C James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-10-24 08:45 -0700
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 11:56 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-24 09:13 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 18:28 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 10:36 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 09:26 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 18:29 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 14:38 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 21:30 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-24 11:30 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 20:36 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-24 21:34 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-24 22:42 +0100
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-24 18:59 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-25 02:48 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-26 04:33 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 17:21 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-26 18:47 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 23:24 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-27 00:29 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-27 01:58 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-27 12:02 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 02:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-10-26 14:29 -0600
                Re: Challenge for Feeb: dealing with large numbers in C Keith Thompson <kst-u@mib.org> - 2019-10-26 13:36 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-26 22:06 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 23:04 +0100
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-27 12:49 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-27 18:20 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-27 22:45 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 00:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-27 14:57 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 01:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 01:44 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 02:31 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 10:42 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 12:45 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 17:39 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-28 20:31 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 20:22 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-28 22:07 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 22:22 +0000
                Re: Challenge for Feeb: dealing with large numbers in C David Brown <david.brown@hesbynett.no> - 2019-10-29 10:17 +0100
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 11:21 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-28 11:05 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 19:26 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 21:08 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-28 21:57 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-28 23:59 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 00:53 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 01:09 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 01:32 +0000
                Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-28 22:44 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-29 03:05 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 11:12 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-29 04:19 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 11:47 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-29 05:03 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 13:16 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 17:13 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 17:35 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ike Naar <ike@sdf.lonestar.org> - 2019-10-30 07:19 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 16:19 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 16:50 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-29 10:03 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-29 17:13 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-29 10:23 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-29 22:20 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-30 03:04 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-30 15:39 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-30 09:02 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-30 19:35 +0000
                Re: Challenge for Feeb: dealing with large numbers in C already5chosen@yahoo.com - 2019-10-30 14:11 -0700
                Re: Challenge for Feeb: dealing with large numbers in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-31 03:34 +0000
                Re: Challenge for Feeb: dealing with large numbers in C Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-04 17:02 -0800
                Re: Challenge for Feeb: dealing with large numbers in C Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2019-10-26 12:30 -0400
                Re: Challenge for Feeb: dealing with large numbers in C Robert Wessel <robertwessel2@yahoo.com> - 2019-10-26 12:03 -0500
                Re: Challenge for Feeb: dealing with large numbers in C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-10-26 14:25 -0600
                Re: Challenge for Feeb: dealing with large numbers in C Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-24 18:06 -0700
        Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 22:44 +0100
          Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-21 19:00 -0400
  Re: Challenge for Feeb: dealing with large numbers in C Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-21 10:20 +0800
    Re: Challenge for Feeb: dealing with large numbers in C Bart <bc@freeuk.com> - 2019-10-21 12:44 +0100
  Re: Challenge for Feeb: dealing with large numbers in C Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-21 10:24 +0800
    Re: Challenge for Feeb: dealing with large numbers in C DFS <nospam@dfs.com> - 2019-10-20 23:05 -0400
      Re: Challenge for Feeb: dealing with large numbers in C Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2019-10-21 11:32 +0800
  Re: Challenge for Feeb: dealing with large numbers in C Autist <autist69@gmail.com> - 2019-10-29 15:15 +0100

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