[font] Fix undefined-behavior when scales are negative

Fixes https://github.com/harfbuzz/harfbuzz/issues/3555
3 years ago · cd05d187c8
parent fc4d42ff99
commit cd05d187c8
1 changed files with 4 additions and 2 deletions
--- 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;
  }