add more conservative check for wayward divide

src/core/SkStroke.cpp

Index: src/core/SkStroke.cpp
diff --git a/src/core/SkStroke.cpp b/src/core/SkStroke.cpp
index e04d14aea5adcf84f95f1c83bfd1ad1404702564..c50d599d1ed5184ca50ecf9550354bf01c478827 100644
--- a/src/core/SkStroke.cpp
+++ b/src/core/SkStroke.cpp
@@ -836,14 +836,12 @@ SkPathStroker::ResultType SkPathStroker::intersectRay(SkQuadConstruct* quadPts,
         return STROKER_RESULT(kSplit_ResultType, depth, quadPts,
                 "(numerA=%g >= 0) == (numerB=%g >= 0)", numerA, numerB);
     }
-    // check to see if the denomerator is teeny relative to the numerator
-    bool validDivide = SkScalarAbs(numerA) * SK_ScalarNearlyZero < SkScalarAbs(denom);
-// the divide check is the same as checking if the scaled denom is nearly zero
-// (commented out because on some platforms the two are not bit-identical)
-//  SkASSERT(!SkScalarNearlyZero(denom / numerA) == validDivide);
+    // check to see if the denominator is teeny relative to the numerator
+    // if the ratio isn't finite, or if the offset by one will be lost, the ratio is too large
+    numerA /= denom;
+    bool validDivide = SkScalarIsFinite(numerA) && numerA != numerA - 1;

[reed1, 2015/11/30 21:24:13]

nit: is "numerA > (numerA - 1)" clearer?
I certainly had to read the comment to understand what this 2nd test was for.
not sure.

     if (validDivide) {
         if (kCtrlPt_RayType == intersectRayType) {
-            numerA /= denom;
             SkPoint* ctrlPt = &quadPts->fQuad[1];
             // the intersection of the tangents need not be on the tangent segment
             // so 0 <= numerA <= 1 is not necessarily true