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Re: Bug in timsort!?

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From Robert Kern <robert.kern@gmail.com>
Subject Re: Bug in timsort!?
Date Wed, 25 Feb 2015 11:34:29 +0000
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Xref csiph.com comp.lang.python:86395

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On 2015-02-24 22:45, Grant Edwards wrote:
> On 2015-02-24, Roy Smith <roy@panix.com> wrote:
>
>> http://envisage-project.eu/proving-android-java-and-python-sorting-algorithm-is-broken-and-how-to-fix-it/
>
> I don't get it.
>
>      3.2 Corrected Python merge_collapse function
>
>      merge_collapse(MergeState *ms)
>      {
>          struct s_slice *p = ms->pending;
>
>          assert(ms);
>          while (ms->n > 1) {
>              Py_ssize_t n = ms->n - 2;
>              if (     n > 0   && p[n-1].len <= p[n].len + p[n+1].len
>                  || (n-1 > 0 &&  p[n-2].len <= p[n].len + p[n-1].len)) {
>                  if (p[n-1].len < p[n+1].len)
>                      --n;
>                  if (merge_at(ms, n) < 0)
>                      return -1;
>              }
>              else if (p[n].len <= p[n+1].len) {
>                       if (merge_at(ms, n) < 0)
>                              return -1;
>              }
>              else
>                  break;
>          }
>          return 0;
>      }
>
> Or does "Python function" mean something else in this context?

"Corrected merge_collapse function [from the Python implementation of TimSort]" 
as opposed to the Java implementation which was also discussed.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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Thread

Bug in timsort!? Roy Smith <roy@panix.com> - 2015-02-24 13:34 -0800
  Re: Bug in timsort!? Zachary Ware <zachary.ware+pylist@gmail.com> - 2015-02-24 15:40 -0600
  Re: Bug in timsort!? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-24 21:49 +0000
    Re: Bug in timsort!? sohcahtoa82@gmail.com - 2015-02-24 14:36 -0800
      Re: Bug in timsort!? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-25 00:38 +0000
  Re: Bug in timsort!? Grant Edwards <invalid@invalid.invalid> - 2015-02-24 22:45 +0000
    Re: Bug in timsort!? Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-24 15:59 -0700
    Re: Bug in timsort!? Robert Kern <robert.kern@gmail.com> - 2015-02-25 11:34 +0000
      Re: Bug in timsort!? Grant Edwards <invalid@invalid.invalid> - 2015-02-25 15:49 +0000
  Re: Bug in timsort!? Chris Angelico <rosuav@gmail.com> - 2015-02-25 10:33 +1100
  Re: Bug in timsort!? MRAB <python@mrabarnett.plus.com> - 2015-02-24 23:38 +0000
  Re: Bug in timsort!? Skip Montanaro <skip.montanaro@gmail.com> - 2015-02-24 17:50 -0600
  Re: Bug in timsort!? Chris Angelico <rosuav@gmail.com> - 2015-02-25 11:07 +1100
    Re: Bug in timsort!? Paddy <paddy3118@gmail.com> - 2015-02-25 01:10 -0800
      Re: Bug in timsort!? Chris Angelico <rosuav@gmail.com> - 2015-02-25 21:11 +1100
  Re: Bug in timsort!? Chris Kaynor <ckaynor@zindagigames.com> - 2015-02-24 16:38 -0800
  Re: Bug in timsort!? Terry Reedy <tjreedy@udel.edu> - 2015-02-24 21:52 -0500
  Re: Bug in timsort!? Dave Angel <davea@davea.name> - 2015-02-24 21:41 -0500
  Re: Bug in timsort!? Ned Deily <nad@acm.org> - 2015-02-25 01:04 -0800
  Re: Bug in timsort!? Sturla Molden <sturla.molden@gmail.com> - 2015-02-25 14:58 +0100
    Re: Bug in timsort!? alister <alister.nospam.ware@ntlworld.com> - 2015-02-25 15:03 +0000
      Re: Bug in timsort!? Zachary Ware <zachary.ware+pylist@gmail.com> - 2015-02-25 09:23 -0600
      Re: Bug in timsort!? Terry Reedy <tjreedy@udel.edu> - 2015-02-25 16:08 -0500
    Re: Bug in timsort!? Roy Smith <roy@panix.com> - 2015-02-25 19:12 -0500
  Re: Bug in timsort!? Jonas Wielicki <jonas@wielicki.name> - 2015-02-25 15:07 +0100
  Re: Bug in timsort!? Chris Angelico <rosuav@gmail.com> - 2015-02-26 01:33 +1100
  Re: Bug in timsort!? Sturla Molden <sturla.molden@gmail.com> - 2015-02-25 16:05 +0100
  Re: Bug in timsort!? Chris Angelico <rosuav@gmail.com> - 2015-02-26 02:11 +1100
  Re: Bug in timsort!? Peter Otten <__peter__@web.de> - 2015-02-25 17:04 +0100
    Re: Bug in timsort!? Mario Figueiredo <marfig@gmail.com> - 2015-02-25 18:22 +0100
      Re: Bug in timsort!? Sturla Molden <sturla.molden@gmail.com> - 2015-02-25 19:41 +0100
      Re: Bug in timsort!? Jonas Wielicki <jonas@wielicki.name> - 2015-02-25 19:46 +0100
      Re: Bug in timsort!? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-25 20:07 +0000
  Re: Bug in timsort!? Sturla Molden <sturla.molden@gmail.com> - 2015-02-25 17:44 +0100
    Re: Bug in timsort!? Mario Figueiredo <marfig@gmail.com> - 2015-02-25 18:29 +0100
    Re: Bug in timsort!? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-26 10:13 +1100
      Re: Bug in timsort!? Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-25 22:51 -0700
  Re: Bug in timsort!? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-25 16:50 +0000
  Re: Bug in timsort!? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-25 16:55 +0000
  Re: Bug in timsort!? Chris Kaynor <ckaynor@zindagigames.com> - 2015-02-25 08:56 -0800
  Re: Bug in timsort!? Chris Angelico <rosuav@gmail.com> - 2015-02-26 04:18 +1100
  Re: Bug in timsort!? Peter Otten <__peter__@web.de> - 2015-02-25 18:21 +0100
  Re: Bug in timsort!? Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-25 12:42 -0700
  Re: Bug in timsort!? Serhiy Storchaka <storchaka@gmail.com> - 2015-02-26 09:33 +0200

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