cc: Do not create separate tilings for almost equal scale factors.

cc/base/math_util_unittest.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/base/math_util.h"
 
 #include <cmath>
 
 #include "cc/test/geometry_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ skipping 366 matching lines @@
   }
 }
 
 TEST(MathUtilTest, RoundDownUnderflow) {
   // Rounding down -123 by 50 is -150, which underflows int8_t, but fits in
   // int16_t.
   EXPECT_FALSE(MathUtil::VerifyRoundDown<int8_t>(-123, 50));
   EXPECT_TRUE(MathUtil::VerifyRoundDown<int16_t>(-123, 50));
 }
 
+TEST(MathUtilTest, AlmostEqualFloats) {
+  float f1 = 7.33907556533813f;

[vmpstr, 2015/10/19 18:58:38]

nit: f1 -> first_value, f2 -> second_value (or something more descriptive)

+  float f2 = 7.33907508850098f;
+
+  EXPECT_TRUE(f1 != f2);
+
+  int max_precision = std::numeric_limits<float>::digits10 - 1;
+
+  // Check with all possible precisions, the almost equal floats (differing by
+  // by small magnitude of epsilon) are same.
+  for (int i = 1; i <= max_precision; ++i) {
+    float f3 = MathUtil::RoundToFixedPrecision(f1, i);

[vmpstr, 2015/10/19 18:58:38]

nit: f3 -> rounded_first_value, f2 -> rounded_second_value (or something more
descriptive)

+    float f4 = MathUtil::RoundToFixedPrecision(f2, i);
+    EXPECT_TRUE(f3 == f4);
+  }
+
+  // Check with different precisions, different values are returned.
+  for (int i = 1; i <= max_precision; ++i) {
+    for (int j = i + 1; j <= max_precision; ++j) {
+      float f3 = MathUtil::RoundToFixedPrecision(f1, i);
+      float f4 = MathUtil::RoundToFixedPrecision(f1, j);
+      EXPECT_FALSE(f3 == f4);
+    }
+  }
+
+  // Different floats differing by some magnitude of epsilon.
+  float f5 = f1 + (10 * std::numeric_limits<float>::epsilon());
+  EXPECT_TRUE(f1 != f5);
+  EXPECT_TRUE(MathUtil::RoundToFixedPrecision(f1, 2) ==
+              MathUtil::RoundToFixedPrecision(f5, 2));
+
+  // Check different floats.
+  float f6 = 7.3f;
+  float f7 = 7.4f;
+  for (int i = 1; i <= max_precision; ++i) {
+    float f8 = MathUtil::RoundToFixedPrecision(f6, i);
+    float f9 = MathUtil::RoundToFixedPrecision(f7, i);
+    EXPECT_FALSE(f8 == f9);
+  }
+}
+
 }  // namespace
 }  // namespace cc