From e5c7ee9f757baa166a96d73b7ec0cb2b1ae23385 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 20 Nov 2019 14:22:01 -0500
Subject: [PATCH] [set] Fix undefined-behavior shift in _previous()

harfbuzz/src/hb-set.hh:138:43: runtime error: shift exponent 64 is too large for 64-bit type 'hb_set_t::page_t::elt_t' (aka 'unsigned long long')
---
 src/hb-set.hh | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/hb-set.hh b/src/hb-set.hh
index 7603526e7..21cb17200 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh
@@ -135,7 +135,11 @@ struct hb_set_t
       unsigned int i = m / ELT_BITS;
       unsigned int j = m & ELT_MASK;
 
-      const elt_t vv = v[i] & ((elt_t (1) << (j + 1)) - 1);
+      /* Fancy mask to avoid shifting by elt_t bitsize, which is undefined. */
+      const elt_t mask = j < 8 * sizeof (elt_t) - 1 ?
+			 ((elt_t (1) << (j + 1)) - 1) :
+			 (elt_t) -1;
+      const elt_t vv = v[i] & mask;
       const elt_t *p = &vv;
       while (true)
       {