ValuePool (#1534)

Summary:


| | Before | After | Δ |
| `sizeof(yoga::Style)` | 208B  | 144B | -64B/-31% |
| `sizeof(yoga::Node)` | 640B  | 576B | -64B/-10% |
| `sizeof(YogaLayoutableShadowNode) ` |  920B | 856B | -64B/-7% |
| `sizeof(YogaLayoutableShadowNode) + sizeof(YogaStylableProps)` | 1296B  | 1168B | -128B/-10% |
| `sizeof(ViewShadowNode)`  |  920B | 856B | -64B/-7% |
| `sizeof(ViewShadowNode) + sizeof(ViewShadowNodeProps)` | 2000B  | 1872B | -128B/-6% |

Differential Revision: D52223122

tests/SmallValueBufferTest.cpp

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gtest/gtest.h>
+#include <yoga/style/SmallValueBuffer.h>
+
+namespace facebook::yoga {
+
+constexpr size_t kBufferSize = 4;
+
+TEST(SmallValueBuffer, copy_assignment_with_overflow) {
+  std::array<uint16_t, kBufferSize + 1> handles;
+
+  SmallValueBuffer<kBufferSize> buffer1;
+  for (size_t i = 0; i < kBufferSize + 1; ++i) {
+    handles[i] = buffer1.push(static_cast<uint32_t>(i));
+  }
+
+  SmallValueBuffer<kBufferSize> buffer2 = buffer1;
+  for (size_t i = 0; i < kBufferSize + 1; ++i) {
+    EXPECT_EQ(buffer2.get32(handles[i]), i);
+  }
+
+  auto handle = buffer1.push(42u);
+  EXPECT_EQ(buffer1.get32(handle), 42);
+
+  EXPECT_THROW({ buffer2.get32(handle); }, std::logic_error);
+}
+
+TEST(SmallValueBuffer, push_32) {
+  auto magic = 88567114u;
+
+  SmallValueBuffer<kBufferSize> buffer;
+  auto handle = buffer.push(magic);
+  EXPECT_EQ(buffer.get32(handle), magic);
+}
+
+TEST(SmallValueBuffer, push_overflow) {
+  uint32_t magic1 = 88567114u;
+  uint32_t magic2 = 351012214u;
+  uint32_t magic3 = 146122128u;
+  uint32_t magic4 = 2171092154u;
+  uint32_t magic5 = 2269016953u;
+
+  SmallValueBuffer<kBufferSize> buffer;
+  EXPECT_EQ(buffer.get32(buffer.push(magic1)), magic1);
+  EXPECT_EQ(buffer.get32(buffer.push(magic2)), magic2);
+  EXPECT_EQ(buffer.get32(buffer.push(magic3)), magic3);
+  EXPECT_EQ(buffer.get32(buffer.push(magic4)), magic4);
+  EXPECT_EQ(buffer.get32(buffer.push(magic5)), magic5);
+}
+
+TEST(SmallValueBuffer, push_64) {
+  uint64_t magic = 88567114ull;
+
+  SmallValueBuffer<kBufferSize> buffer;
+  auto handle = buffer.push(magic);
+  EXPECT_EQ(buffer.get64(handle), magic);
+}
+
+TEST(SmallValueBuffer, push_64_overflow) {
+  uint64_t magic1 = 1401612388342512ull;
+  uint64_t magic2 = 118712305386210ull;
+  uint64_t magic3 = 752431801563359011ull;
+  uint64_t magic4 = 118138934255546108ull;
+  uint64_t magic5 = 237115443124116111ull;
+
+  SmallValueBuffer<kBufferSize> buffer;
+  EXPECT_EQ(buffer.get64(buffer.push(magic1)), magic1);
+  EXPECT_EQ(buffer.get64(buffer.push(magic2)), magic2);
+  EXPECT_EQ(buffer.get64(buffer.push(magic3)), magic3);
+  EXPECT_EQ(buffer.get64(buffer.push(magic4)), magic4);
+  EXPECT_EQ(buffer.get64(buffer.push(magic5)), magic5);
+}
+
+TEST(SmallValueBuffer, push_64_after_32) {}
+
+TEST(SmallValueBuffer, push_32_after_64) {}
+
+TEST(SmallValueBuffer, get32_oob) {}
+
+TEST(SmallValueBuffer, get64_oob) {}
+
+TEST(SmallValueBuffer, replace_32_with_32) {}
+
+TEST(SmallValueBuffer, replace_32_with_64) {}
+
+TEST(SmallValueBuffer, replace_64_with_32) {}
+
+TEST(SmallValueBuffer, replace_64_with_64) {}
+
+} // namespace facebook::yoga