Fixing edge case issue in Yoga where text node was unnecessary rounded down

Summary: There was an uncovered edge case where number close to the whole was forced to round down because it was considered non-whole and had forced flooring. This diff covers that + adds a bunch of test cases to cover rounding function

Reviewed By: emilsjolander

Differential Revision: D5465632

fbshipit-source-id: 57e11092a97eba5dd76daad15fa8619535ff9c1b

Author: Georgiy Kassabli

tests/YGRoundingFunctionTest.cpp

@@ -0,0 +1,31 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#include <gtest/gtest.h>
+
+#include <yoga/Yoga.h>
+#include <yoga/Yoga-internal.h>
+
+TEST(YogaTest, rounding_value) {
+  // Test that whole numbers are rounded to whole despite ceil/floor flags
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(6.000001, 2.0, false, false));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(6.000001, 2.0, true, false));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(6.000001, 2.0, false, true));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.999999, 2.0, false, false));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.999999, 2.0, true, false));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.999999, 2.0, false, true));
+
+  // Test that numbers with fraction are rounded correctly accounting for ceil/floor flags
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(6.01, 2.0, false, false));
+  ASSERT_FLOAT_EQ(6.5, YGRoundValueToPixelGrid(6.01, 2.0, true, false));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(6.01, 2.0, false, true));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.99, 2.0, false, false));
+  ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.99, 2.0, true, false));
+  ASSERT_FLOAT_EQ(5.5, YGRoundValueToPixelGrid(5.99, 2.0, false, true));
+}

yoga/Yoga-internal.h

@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#pragma once
+
+YG_EXTERN_C_BEGIN
+
+WIN_EXPORT float YGRoundValueToPixelGrid(const float value,
+                                         const float pointScaleFactor,
+                                         const bool forceCeil,
+                                         const bool forceFloor);
+
+YG_EXTERN_C_END

yoga/Yoga.c

@@ -11,6 +11,7 @@
 
 #include "YGNodeList.h"
 #include "Yoga.h"
+#include "Yoga-internal.h"
 
 #ifdef _MSC_VER
 #include <float.h>
@@ -3158,20 +3159,24 @@ static inline bool YGMeasureModeNewMeasureSizeIsStricterAndStillValid(YGMeasureM
          lastSize > size && (lastComputedSize <= size || YGFloatsEqual(size, lastComputedSize));
 }
 
-static float YGRoundValueToPixelGrid(const float value,
+float YGRoundValueToPixelGrid(const float value,
                                      const float pointScaleFactor,
                                      const bool forceCeil,
                                      const bool forceFloor) {
   float scaledValue = value * pointScaleFactor;
   float fractial = fmodf(scaledValue, 1.0);
   if (YGFloatsEqual(fractial, 0)) {
-    // Still remove fractial as fractial could be  extremely small.
+    // First we check if the value is already rounded
     scaledValue = scaledValue - fractial;
+  } else if (YGFloatsEqual(fractial, 1.0)) {
+    scaledValue = scaledValue - fractial + 1.0;
   } else if (forceCeil) {
+    // Next we check if we need to use forced rounding
     scaledValue = scaledValue - fractial + 1.0;
   } else if (forceFloor) {
     scaledValue = scaledValue - fractial;
   } else {
+    // Finally we just round the value
     scaledValue = scaledValue - fractial + (fractial >= 0.5f ? 1.0 : 0);
   }
   return scaledValue / pointScaleFactor;