commit cd05d187c893ad0bcf754393a865c417d5cff36d
author Behdad Esfahbod <behdad@behdad.org> Wed Jun 01 07:27:30 2022 -0600
committer Behdad Esfahbod <behdad@behdad.org> Wed Jun 01 07:27:53 2022 -0600
tree 839dbd45ea7f07d326612cd8087f656b3b7cff9d
parent fc4d42ff99018f9f640d3191bcd621c547ed61ea

[font] Fix undefined-behavior when scales are negative

Fixes https://github.com/harfbuzz/harfbuzz/issues/3555

src/hb-font.hh

diff --git a/src/hb-font.hh b/src/hb-font.hh
index 952beab..abc8bb3 100644
--- a/src/hb-font.hh
+++ b/src/hb-font.hh
@@ -631,8 +631,10 @@
   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;
   }