Fix bug in cubic derivative coefficient with missing parens

src/utils/SkCurveMeasure.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCurveMeasure.h"
 #include "SkGeometry.h"
 
@@ skipping 88 matching lines @@
     switch (fSegType) {
         case kQuad_SegType: {
             float Ax = pts[0].x();
             float Bx = pts[1].x();
             float Cx = pts[2].x();
             float Ay = pts[0].y();
             float By = pts[1].y();
             float Cy = pts[2].y();
 
             // precompute coefficients for derivative
-            xCoeff[0] = Sk8f(2.0f*(Ax - 2*Bx + Cx));
-            xCoeff[1] = Sk8f(2.0f*(Bx - Ax));
+            xCoeff[0] = Sk8f(2*(Ax - 2*Bx + Cx));
+            xCoeff[1] = Sk8f(2*(Bx - Ax));
 
-            yCoeff[0] = Sk8f(2.0f*(Ay - 2*By + Cy));
-            yCoeff[1] = Sk8f(2.0f*(By - Ay));
+            yCoeff[0] = Sk8f(2*(Ay - 2*By + Cy));
+            yCoeff[1] = Sk8f(2*(By - Ay));
         }
             break;
         case kCubic_SegType:
         {
             float Ax = pts[0].x();
             float Bx = pts[1].x();
             float Cx = pts[2].x();
             float Dx = pts[3].x();
             float Ay = pts[0].y();
             float By = pts[1].y();
             float Cy = pts[2].y();
             float Dy = pts[3].y();
 
             // precompute coefficients for derivative
-            xCoeff[0] = Sk8f(3.0f*(-Ax + 3.0f*(Bx - Cx) + Dx));
-            xCoeff[1] = Sk8f(3.0f*(2.0f*(Ax - 2.0f*Bx + Cx)));
-            xCoeff[2] = Sk8f(3.0f*(-Ax + Bx));
+            xCoeff[0] = Sk8f(3*(-Ax + 3*(Bx - Cx) + Dx));
+            xCoeff[1] = Sk8f(6*(Ax - 2*Bx + Cx));
+            xCoeff[2] = Sk8f(3*(-Ax + Bx));
 
-            yCoeff[0] = Sk8f(3.0f*(-Ay + 3.0f*(By - Cy) + Dy));
-            yCoeff[1] = Sk8f(3.0f * -Ay + By + 2.0f*(Ay - 2.0f*By + Cy));
-            yCoeff[2] = Sk8f(3.0f*(-Ay + By));
+            yCoeff[0] = Sk8f(3*(-Ay + 3*(By - Cy) + Dy));
+            yCoeff[1] = Sk8f(6*(Ay - 2*By + Cy));
+            yCoeff[2] = Sk8f(3*(-Ay + By));
         }
             break;
         case kConic_SegType:
             UNIMPLEMENTED;
             break;
         default:
             UNIMPLEMENTED;
     }
 }
 
@@ skipping 156 matching lines @@
     if (time) {
         *time = t;
     }
     if (pos) {
         *pos = evaluate(fPts, fSegType, t);
     }
     if (tan) {
         *tan = evaluateDerivative(fPts, fSegType, t);
     }
 }