pin before calling acos

src/core/SkGeometry.cpp

Index: src/core/SkGeometry.cpp
diff --git a/src/core/SkGeometry.cpp b/src/core/SkGeometry.cpp
index 7256b9e517ec5e401c6e6838dbc6245392b99f85..760b9b4e1c751543569750277a7fe2c5a6feca88 100644
--- a/src/core/SkGeometry.cpp
+++ b/src/core/SkGeometry.cpp
@@ -743,7 +743,7 @@ static int solve_cubic_poly(const SkScalar coeff[4], SkScalar tValues[3]) {
     SkScalar    r;
 
     if (R2MinusQ3 < 0) { // we have 3 real roots
-        SkScalar theta = SkScalarACos(R / SkScalarSqrt(Q3));
+        SkScalar theta = SkScalarACos(SkScalarPin(R / SkScalarSqrt(Q3), -1, 1));  // bug.skia.org/5222

[reed1, 2016/05/25 17:12:52]

Perhaps ah comment as to why we pin ...
1. the divide/root can be anything
2. the divide/root can, due to finite precisions, be slightly outside of -1...1
3. the divide/root can occasionally generate inf. or Nan.

         SkScalar neg2RootQ = -2 * SkScalarSqrt(Q);
 
         r = neg2RootQ * SkScalarCos(theta/3) - adiv3;