[set] Fix page_map[] indexing in backward loop.
Fixes https://github.com/behdad/harfbuzz/issues/579.
diff --git a/src/hb-set-private.hh b/src/hb-set-private.hh
index df4325a..c970b89 100644
--- a/src/hb-set-private.hh
+++ b/src/hb-set-private.hh
@@ -313,13 +313,13 @@
b = nb;
for (; a && b; )
{
- if (page_map[a].major == other->page_map[b].major)
+ if (page_map[a - 1].major == other->page_map[b - 1].major)
{
a--;
b--;
Op::process (page_at (--count).v, page_at (a).v, other->page_at (b).v);
}
- else if (page_map[a].major > other->page_map[b].major)
+ else if (page_map[a - 1].major > other->page_map[b - 1].major)
{
a--;
if (Op::passthru_left)
