Added BitUtils

Summary:
Adds BitUtils to be used later instead of Bitfield.h

##Changelog:
[Internal][Yoga] : Adds BitUtils to be used later instead of Bitfield.h

Reviewed By: astreet

Differential Revision: D18519609

fbshipit-source-id: 8353929543505a7d80d66281adb801d34372beed

yoga/BitUtils.h

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <cstdio>
+#include <cstdint>
+#include "YGEnums.h"
+
+namespace facebook {
+namespace yoga {
+
+namespace detail {
+
+constexpr size_t log2ceilFn(size_t n) {
+  return n < 1 ? 0 : (1 + log2ceilFn(n / 2));
+}
+
+constexpr int mask(size_t bitWidth, size_t index) {
+  return ((1 << bitWidth) - 1) << index;
+}
+
+// The number of bits necessary to represent enums defined with YG_ENUM_SEQ_DECL
+template <typename Enum>
+constexpr size_t bitWidthFn() {
+  static_assert(
+      enums::count<Enum>() > 0, "Enums must have at least one entries");
+  return log2ceilFn(enums::count<Enum>() - 1);
+}
+
+template <typename Enum>
+constexpr Enum getEnumData(int flags, size_t index) {
+  return static_cast<Enum>((flags & mask(bitWidthFn<Enum>(), index)) >> index);
+}
+
+template <typename Enum>
+void setEnumData(uint32_t& flags, size_t index, int newValue) {
+  flags = (flags & ~mask(bitWidthFn<Enum>(), index)) |
+      ((newValue << index) & (mask(bitWidthFn<Enum>(), index)));
+}
+
+template <typename Enum>
+void setEnumData(uint8_t& flags, size_t index, int newValue) {
+  flags = (flags & ~mask(bitWidthFn<Enum>(), index)) |
+      ((newValue << index) & (mask(bitWidthFn<Enum>(), index)));
+}
+
+constexpr bool getBooleanData(int flags, size_t index) {
+  return (flags >> index) & 1;
+}
+
+inline void setBooleanData(uint8_t& flags, size_t index, bool value) {
+  if (value) {
+    flags |= 1 << index;
+  } else {
+    flags &= ~(1 << index);
+  }
+}
+
+} // namespace detail
+} // namespace yoga
+} // namespace facebook