[Fontconfig-bugs] [Bug 82228] New: OpenType weight between 0 and 100 could result in assertion in FcWeightFromOpenType

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=82228

          Priority: medium
            Bug ID: 82228
          Assignee: fontconfig-bugs at lists.freedesktop.org
           Summary: OpenType weight between 0 and 100 could result in
                    assertion in FcWeightFromOpenType
        QA Contact: freedesktop at behdad.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: daphnediane at mac.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: library
           Product: fontconfig

Calling FcWeightFromOpenType with ot_weight between 1 and 99 triggers an
assertion. lerp will get called with x = ot_weight, x1 = 0, x2 = 100, y1 = 0,
y2 = 0. It will then compute dy = y2 - y1 = 0. Which will cause assert ( dx > 0
&& dy > 0 && x1 <= x && x <= x2 ) to fail as dy is 0. Seems like if dy == 0,
then it should return y1.

Possible patch

diff --git a/src/fcweight.c b/src/fcweight.c
index 87bbe67..4def775 100644
--- a/src/fcweight.c
+++ b/src/fcweight.c
@@ -45,6 +45,7 @@ static int lerp(int x, int x1, int x2, int y1, int y2)
 {
   int dx = x2 - x1;
   int dy = y2 - y1;
+  if (dy == 0 && x1 <= x && x <= x2) return y1;
   assert (dx > 0 && dy > 0 && x1 <= x && x <= x2);
   return y1 + (dy*(x-x1) + dx/2) / dx;
 }

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