From: Benjamin Peterson <benjamin@python.org>
Date: Wed, 25 Feb 2015 15:12:26 +0000 (-0500)
Subject: fix merge_collapse to actually maintain the invariant it purports to (closes #23515)
X-Git-Tag: v3.5.0a2~90^2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=b808d590a24066bc03d21b55ed5e890a012477a8;p=python

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"
---

diff --git a/Objects/listobject.c b/Objects/listobject.c
index fd5a72af8d..b6c1d784fb 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -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)