Back out Stack D13119110..D13236159

Summary: backout, causes failures

Reviewed By: adityasharat

Differential Revision: D13376210

fbshipit-source-id: 1fa8823f2dce601c47738f34ddb2674288197e79

csharp/Facebook.Yoga/YogaConstants.cs

@@ -1,4 +1,4 @@
-/**
+/**
  * Copyright (c) Facebook, Inc. and its affiliates.
  *
  * This source code is licensed under the MIT license found in the
@@ -9,11 +9,28 @@ namespace Facebook.Yoga
 {
     public static class YogaConstants
     {
-        public const float Undefined = float.NaN;
+        /**
+         * Large positive number signifies that the property(float) is undefined. Earlier we used to have
+         * YGundefined as NAN, but the downside of this is that we can't use -ffast-math compiler flag as
+         * it assumes all floating-point calculation involve and result into finite numbers. For more
+         * information regarding -ffast-math compiler flag in clang, have a look at
+         * https://clang.llvm.org/docs/UsersManual.html#cmdoption-ffast-math
+         */
+        public const float Undefined = 10E20F;
 
         public static bool IsUndefined(float value)
         {
-            return float.IsNaN(value);
+            // Value of a float in the case of it being not defined is 10.1E20. Earlier it used to be NAN,
+            // the benefit of which
+            // was that if NAN is involved in any mathematical expression the result was NAN. But since we
+            // want to have `-ffast-math`
+            // flag being used by compiler which assumes that the floating point values are not NAN and Inf,
+            // we represent YGUndefined as 10.1E20.
+            // But now if YGUndefined is involved in any mathematical operations this value(10.1E20) would
+            // change.
+            // So the following check makes sure that if the value is outside a range (-10E8, 10E8) then it
+            // is undefined.
+            return value >= 10E8F || value <= -10E8;
         }
 
         public static bool IsUndefined(YogaValue value)