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manual: Remove incorrect claim that qsort() can be stabilized 

Under certain conditions on the size of the array and its items,
qsort() may fall back to an in-place quicksort if it cannot allocate
memory for a temporary array with malloc().  This algorithm is not a
stable sort even if the comparison function is written in the
described manner.

Fixes #10672.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
This commit is contained in:
Anders Kaseorg 2014-07-02 21:17:50 -04:00 committed by Ondřej Bílka
parent b987c89126
commit f5f46d51f7
3 changed files with 16 additions and 11 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2014-12-10 Anders Kaseorg <andersk@MIT.EDU>
[BZ #10672]
* manual/search.texi: (Array Sort Function): Remove claim how make
qsort stable.
2014-12-10 Andreas Schwab <schwab@suse.de>
[BZ #12847]

12
NEWS
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@ -9,12 +9,12 @@ Version 2.21
* The following bugs are resolved with this release:
6652, 12847, 12926, 13862, 14132, 14138, 14171, 14498, 15215, 15884,
16469, 16619, 16740, 16857, 17192, 17266, 17344, 17363, 17370, 17371,
17411, 17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555, 17570,
17571, 17572, 17573, 17574, 17581, 17582, 17583, 17584, 17585, 17589,
17594, 17601, 17608, 17616, 17625, 17633, 17647, 17653, 17664, 17665,
17668, 17682.
6652, 10672, 12847, 12926, 13862, 14132, 14138, 14171, 14498, 15215,
15884, 16469, 16619, 16740, 16857, 17192, 17266, 17344, 17363, 17370,
17371, 17411, 17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555,
17570, 17571, 17572, 17573, 17574, 17581, 17582, 17583, 17584, 17585,
17589, 17594, 17601, 17608, 17616, 17625, 17633, 17647, 17653, 17664,
17665, 17668, 17682.
* CVE-2104-7817 The wordexp function could ignore the WRDE_NOCMD flag
under certain input conditions resulting in the execution of a shell for

9
manual/search.texi
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@ -180,11 +180,10 @@ This can make a difference when the comparison considers only part of
the elements. Two elements with the same sort key may differ in other
respects.
If you want the effect of a stable sort, you can get this result by
writing the comparison function so that, lacking other reason
distinguish between two elements, it compares them by their addresses.
Note that doing this may make the sorting algorithm less efficient, so
do it only if necessary.
The addresses passed to the comparison function need not correspond with
the original location of the objects, and need not even lie within the
original array. The only way to perform a stable sort with @var{qsort}
is to first augment the objects with a monotonic counter of some kind.
Here is a simple example of sorting an array of doubles in numerical
order, using the comparison function defined above (@pxref{Comparison