From cd05d187c893ad0bcf754393a865c417d5cff36d Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 1 Jun 2022 07:27:30 -0600
Subject: [PATCH] [font] Fix undefined-behavior when scales are negative

Fixes https://github.com/harfbuzz/harfbuzz/issues/3555
---
 src/hb-font.hh | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/hb-font.hh b/src/hb-font.hh
index 952beabe1..abc8bb3ba 100644
--- a/src/hb-font.hh
+++ b/src/hb-font.hh
@@ -631,8 +631,10 @@ struct hb_font_t
   void mults_changed ()
   {
     signed upem = face->get_upem ();
-    x_mult = ((int64_t) x_scale << 16) / upem;
-    y_mult = ((int64_t) y_scale << 16) / upem;
+    bool x_neg = x_scale < 0;
+    x_mult = (x_neg ? -((int64_t) -x_scale << 16) : ((int64_t) x_scale << 16)) / upem;
+    bool y_neg = y_scale < 0;
+    y_mult = (y_neg ? -((int64_t) -y_scale << 16) : ((int64_t) y_scale << 16)) / upem;
     slant_xy = y_scale ? slant * x_scale / y_scale : 0.f;
   }