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fix merge_collapse to actually maintain the invariant it purports to (closes #23515) 

See
de Gouw, Stijn and Rot, Jurriaan and de Boer, Frank S and Bubel, Richard and Hähnle, Reiner
"OpenJDK’s java.utils.Collection.sort() is broken: The good, the bad and the worst case"
This commit is contained in:
Benjamin Peterson 2015-02-25 10:12:26 -05:00
parent 83704963c0
commit b808d590a2
1 changed files with 2 additions and 1 deletions
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3
Objects/listobject.c
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@ -1832,7 +1832,8 @@ merge_collapse(MergeState *ms)
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) {
if ((n > 0 && p[n-1].len <= p[n].len + p[n+1].len) ||
(n > 1 && p[n-2].len <= p[n-1].len + p[n].len)) {
if (p[n-1].len < p[n+1].len)
--n;
if (merge_at(ms, n) < 0)