+static const struct string_list *prereleases;
+static int initialized;
+
+/*
+ * p1 and p2 point to the first different character in two strings. If
+ * either p1 or p2 starts with a prerelease suffix, it will be forced
+ * to be on top.
+ *
+ * If both p1 and p2 start with (different) suffix, the order is
+ * determined by config file.
+ *
+ * Note that we don't have to deal with the situation when both p1 and
+ * p2 start with the same suffix because the common part is already
+ * consumed by the caller.
+ *
+ * Return non-zero if *diff contains the return value for versioncmp()
+ */
+static int swap_prereleases(const void *p1_,
+ const void *p2_,
+ int *diff)
+{
+ const char *p1 = p1_;
+ const char *p2 = p2_;
+ int i, i1 = -1, i2 = -1;
+
+ for (i = 0; i < prereleases->nr; i++) {
+ const char *suffix = prereleases->items[i].string;
+ if (i1 == -1 && starts_with(p1, suffix))
+ i1 = i;
+ if (i2 == -1 && starts_with(p2, suffix))
+ i2 = i;
+ }
+ if (i1 == -1 && i2 == -1)
+ return 0;
+ if (i1 >= 0 && i2 >= 0)
+ *diff = i1 - i2;
+ else if (i1 >= 0)
+ *diff = -1;
+ else /* if (i2 >= 0) */
+ *diff = 1;
+ return 1;
+}