Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 135 insertions, 0 deletions

diff --git a/mfbt/TypedEnumBits.h b/mfbt/TypedEnumBits.h
new file mode 100644
index 0000000000..b431d90e02
--- /dev/null
+++ b/mfbt/TypedEnumBits.h
@@ -0,0 +1,135 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS allows using a typed enum as bit flags.
+ */
+
+#ifndef mozilla_TypedEnumBits_h
+#define mozilla_TypedEnumBits_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/IntegerTypeTraits.h"
+
+namespace mozilla {
+
+/*
+ * The problem that CastableTypedEnumResult aims to solve is that
+ * typed enums are not convertible to bool, and there is no way to make them
+ * be, yet user code wants to be able to write
+ *
+ *   if (myFlags & Flags::SOME_PARTICULAR_FLAG)              (1)
+ *
+ * There are different approaches to solving this. Most of them require
+ * adapting user code. For example, we could implement operator! and have
+ * the user write
+ *
+ *   if (!!(myFlags & Flags::SOME_PARTICULAR_FLAG))          (2)
+ *
+ * Or we could supply a IsNonZero() or Any() function returning whether
+ * an enum value is nonzero, and have the user write
+ *
+ *   if (Any(Flags & Flags::SOME_PARTICULAR_FLAG))           (3)
+ *
+ * But instead, we choose to preserve the original user syntax (1) as it
+ * is inherently more readable, and to ease porting existing code to typed
+ * enums. We achieve this by having operator& and other binary bitwise
+ * operators have as return type a class, CastableTypedEnumResult,
+ * that wraps a typed enum but adds bool convertibility.
+ */
+template <typename E>
+class CastableTypedEnumResult {
+ private:
+  const E mValue;
+
+ public:
+  explicit constexpr CastableTypedEnumResult(E aValue) : mValue(aValue) {}
+
+  constexpr operator E() const { return mValue; }
+
+  template <typename DestinationType>
+  explicit constexpr operator DestinationType() const {
+    return DestinationType(mValue);
+  }
+
+  constexpr bool operator!() const { return !bool(mValue); }
+};
+
+#define MOZ_CASTABLETYPEDENUMRESULT_BINOP(Op, OtherType, ReturnType)        \
+  template <typename E>                                                     \
+  constexpr ReturnType operator Op(const OtherType& aE,                     \
+                                   const CastableTypedEnumResult<E>& aR) {  \
+    return ReturnType(aE Op OtherType(aR));                                 \
+  }                                                                         \
+  template <typename E>                                                     \
+  constexpr ReturnType operator Op(const CastableTypedEnumResult<E>& aR,    \
+                                   const OtherType& aE) {                   \
+    return ReturnType(OtherType(aR) Op aE);                                 \
+  }                                                                         \
+  template <typename E>                                                     \
+  constexpr ReturnType operator Op(const CastableTypedEnumResult<E>& aR1,   \
+                                   const CastableTypedEnumResult<E>& aR2) { \
+    return ReturnType(OtherType(aR1) Op OtherType(aR2));                    \
+  }
+
+MOZ_CASTABLETYPEDENUMRESULT_BINOP(|, E, CastableTypedEnumResult<E>)
+MOZ_CASTABLETYPEDENUMRESULT_BINOP(&, E, CastableTypedEnumResult<E>)
+MOZ_CASTABLETYPEDENUMRESULT_BINOP(^, E, CastableTypedEnumResult<E>)
+MOZ_CASTABLETYPEDENUMRESULT_BINOP(==, E, bool)
+MOZ_CASTABLETYPEDENUMRESULT_BINOP(!=, E, bool)
+
+template <typename E>
+constexpr CastableTypedEnumResult<E> operator~(
+    const CastableTypedEnumResult<E>& aR) {
+  return CastableTypedEnumResult<E>(~(E(aR)));
+}
+
+#define MOZ_CASTABLETYPEDENUMRESULT_COMPOUND_ASSIGN_OP(Op)        \
+  template <typename E>                                           \
+  E& operator Op(E& aR1, const CastableTypedEnumResult<E>& aR2) { \
+    return aR1 Op E(aR2);                                         \
+  }
+
+MOZ_CASTABLETYPEDENUMRESULT_COMPOUND_ASSIGN_OP(&=)
+MOZ_CASTABLETYPEDENUMRESULT_COMPOUND_ASSIGN_OP(|=)
+MOZ_CASTABLETYPEDENUMRESULT_COMPOUND_ASSIGN_OP(^=)
+
+#undef MOZ_CASTABLETYPEDENUMRESULT_COMPOUND_ASSIGN_OP
+
+#undef MOZ_CASTABLETYPEDENUMRESULT_BINOP
+
+namespace detail {
+template <typename E>
+struct UnsignedIntegerTypeForEnum : UnsignedStdintTypeForSize<sizeof(E)> {};
+}  // namespace detail
+
+}  // namespace mozilla
+
+#define MOZ_MAKE_ENUM_CLASS_BINOP_IMPL(Name, Op)                       \
+  inline constexpr mozilla::CastableTypedEnumResult<Name> operator Op( \
+      Name a, Name b) {                                                \
+    typedef mozilla::CastableTypedEnumResult<Name> Result;             \
+    typedef mozilla::detail::UnsignedIntegerTypeForEnum<Name>::Type U; \
+    return Result(Name(U(a) Op U(b)));                                 \
+  }                                                                    \
+                                                                       \
+  inline Name& operator Op##=(Name& a, Name b) { return a = a Op b; }
+
+/**
+ * MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS generates standard bitwise operators
+ * for the given enum type. Use this to enable using an enum type as bit-field.
+ */
+#define MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(Name)                           \
+  MOZ_MAKE_ENUM_CLASS_BINOP_IMPL(Name, |)                                     \
+  MOZ_MAKE_ENUM_CLASS_BINOP_IMPL(Name, &)                                     \
+  MOZ_MAKE_ENUM_CLASS_BINOP_IMPL(Name, ^)                                     \
+  inline constexpr mozilla::CastableTypedEnumResult<Name> operator~(Name a) { \
+    typedef mozilla::CastableTypedEnumResult<Name> Result;                    \
+    typedef mozilla::detail::UnsignedIntegerTypeForEnum<Name>::Type U;        \
+    return Result(Name(~(U(a))));                                             \
+  }
+
+#endif  // mozilla_TypedEnumBits_h