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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Tue, 24 Feb 2015 15:59:34 -0700
Subject: Re: Bug in timsort!?
To: Python <python-list@python.org>
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Xref: csiph.com comp.lang.python:86352

On Tue, Feb 24, 2015 at 3:45 PM, Grant Edwards <invalid@invalid.invalid> 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?

Recall that CPython is implemented in C. ;-)