FTL: Pull Flags into namespace
Bug: 185536303
Test: Build
Change-Id: Ia9aafc78565414815dfc14732ce85b06fa96e17b
diff --git a/include/ftl/flags.h b/include/ftl/flags.h
new file mode 100644
index 0000000..70aaa0e
--- /dev/null
+++ b/include/ftl/flags.h
@@ -0,0 +1,225 @@
+/*
+ * Copyright 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <ftl/enum.h>
+#include <ftl/string.h>
+
+#include <bitset>
+#include <cstdint>
+#include <iterator>
+#include <string>
+#include <type_traits>
+
+// TODO(b/185536303): Align with FTL style.
+
+namespace android::ftl {
+
+/* A class for handling flags defined by an enum or enum class in a type-safe way. */
+template <typename F>
+class Flags {
+ // F must be an enum or its underlying type is undefined. Theoretically we could specialize this
+ // further to avoid this restriction but in general we want to encourage the use of enums
+ // anyways.
+ static_assert(std::is_enum_v<F>, "Flags type must be an enum");
+ using U = std::underlying_type_t<F>;
+
+public:
+ constexpr Flags(F f) : mFlags(static_cast<U>(f)) {}
+ constexpr Flags() : mFlags(0) {}
+ constexpr Flags(const Flags<F>& f) : mFlags(f.mFlags) {}
+
+ // Provide a non-explicit construct for non-enum classes since they easily convert to their
+ // underlying types (e.g. when used with bitwise operators). For enum classes, however, we
+ // should force them to be explicitly constructed from their underlying types to make full use
+ // of the type checker.
+ template <typename T = U>
+ constexpr Flags(T t, std::enable_if_t<!is_scoped_enum_v<F>, T>* = nullptr) : mFlags(t) {}
+
+ template <typename T = U>
+ explicit constexpr Flags(T t, std::enable_if_t<is_scoped_enum_v<F>, T>* = nullptr)
+ : mFlags(t) {}
+
+ class Iterator {
+ using Bits = std::uint64_t;
+ static_assert(sizeof(U) <= sizeof(Bits));
+
+ public:
+ constexpr Iterator() = default;
+ Iterator(Flags<F> flags) : mRemainingFlags(flags.mFlags) { (*this)++; }
+
+ // Pre-fix ++
+ Iterator& operator++() {
+ if (mRemainingFlags.none()) {
+ mCurrFlag = 0;
+ } else {
+ // TODO: Replace with std::countr_zero in C++20.
+ const Bits bit = static_cast<Bits>(__builtin_ctzll(mRemainingFlags.to_ullong()));
+ mRemainingFlags.reset(static_cast<std::size_t>(bit));
+ mCurrFlag = static_cast<U>(static_cast<Bits>(1) << bit);
+ }
+ return *this;
+ }
+
+ // Post-fix ++
+ Iterator operator++(int) {
+ Iterator iter = *this;
+ ++*this;
+ return iter;
+ }
+
+ bool operator==(Iterator other) const {
+ return mCurrFlag == other.mCurrFlag && mRemainingFlags == other.mRemainingFlags;
+ }
+
+ bool operator!=(Iterator other) const { return !(*this == other); }
+
+ F operator*() const { return F{mCurrFlag}; }
+
+ // iterator traits
+
+ // In the future we could make this a bidirectional const iterator instead of a forward
+ // iterator but it doesn't seem worth the added complexity at this point. This could not,
+ // however, be made a non-const iterator as assigning one flag to another is a non-sensical
+ // operation.
+ using iterator_category = std::input_iterator_tag;
+ using value_type = F;
+ // Per the C++ spec, because input iterators are not assignable the iterator's reference
+ // type does not actually need to be a reference. In fact, making it a reference would imply
+ // that modifying it would change the underlying Flags object, which is obviously wrong for
+ // the same reason this can't be a non-const iterator.
+ using reference = F;
+ using difference_type = void;
+ using pointer = void;
+
+ private:
+ std::bitset<sizeof(Bits) * 8> mRemainingFlags;
+ U mCurrFlag = 0;
+ };
+
+ /*
+ * Tests whether the given flag is set.
+ */
+ bool test(F flag) const {
+ U f = static_cast<U>(flag);
+ return (f & mFlags) == f;
+ }
+
+ /* Tests whether any of the given flags are set */
+ bool any(Flags<F> f) const { return (mFlags & f.mFlags) != 0; }
+
+ /* Tests whether all of the given flags are set */
+ bool all(Flags<F> f) const { return (mFlags & f.mFlags) == f.mFlags; }
+
+ Flags<F> operator|(Flags<F> rhs) const { return static_cast<F>(mFlags | rhs.mFlags); }
+ Flags<F>& operator|=(Flags<F> rhs) {
+ mFlags = mFlags | rhs.mFlags;
+ return *this;
+ }
+
+ Flags<F> operator&(Flags<F> rhs) const { return static_cast<F>(mFlags & rhs.mFlags); }
+ Flags<F>& operator&=(Flags<F> rhs) {
+ mFlags = mFlags & rhs.mFlags;
+ return *this;
+ }
+
+ Flags<F> operator^(Flags<F> rhs) const { return static_cast<F>(mFlags ^ rhs.mFlags); }
+ Flags<F>& operator^=(Flags<F> rhs) {
+ mFlags = mFlags ^ rhs.mFlags;
+ return *this;
+ }
+
+ Flags<F> operator~() { return static_cast<F>(~mFlags); }
+
+ bool operator==(Flags<F> rhs) const { return mFlags == rhs.mFlags; }
+ bool operator!=(Flags<F> rhs) const { return !operator==(rhs); }
+
+ Flags<F>& operator=(const Flags<F>& rhs) {
+ mFlags = rhs.mFlags;
+ return *this;
+ }
+
+ inline Flags<F>& clear(Flags<F> f = static_cast<F>(~static_cast<U>(0))) {
+ return *this &= ~f;
+ }
+
+ Iterator begin() const { return Iterator(*this); }
+
+ Iterator end() const { return Iterator(); }
+
+ /*
+ * Returns the stored set of flags.
+ *
+ * Note that this returns the underlying type rather than the base enum class. This is because
+ * the value is no longer necessarily a strict member of the enum since the returned value could
+ * be multiple enum variants OR'd together.
+ */
+ U get() const { return mFlags; }
+
+ std::string string() const {
+ std::string result;
+ bool first = true;
+ U unstringified = 0;
+ for (const F f : *this) {
+ if (const auto flagName = flag_name(f)) {
+ appendFlag(result, flagName.value(), first);
+ } else {
+ unstringified |= static_cast<U>(f);
+ }
+ }
+
+ if (unstringified != 0) {
+ constexpr auto radix = sizeof(U) == 1 ? Radix::kBin : Radix::kHex;
+ appendFlag(result, to_string(unstringified, radix), first);
+ }
+
+ if (first) {
+ result += "0x0";
+ }
+
+ return result;
+ }
+
+private:
+ U mFlags;
+
+ static void appendFlag(std::string& str, const std::string_view& flag, bool& first) {
+ if (first) {
+ first = false;
+ } else {
+ str += " | ";
+ }
+ str += flag;
+ }
+};
+
+// This namespace provides operator overloads for enum classes to make it easier to work with them
+// as flags. In order to use these, add them via a `using namespace` declaration.
+namespace flag_operators {
+
+template <typename F, typename = std::enable_if_t<is_scoped_enum_v<F>>>
+inline Flags<F> operator~(F f) {
+ return static_cast<F>(~to_underlying(f));
+}
+
+template <typename F, typename = std::enable_if_t<is_scoped_enum_v<F>>>
+Flags<F> operator|(F lhs, F rhs) {
+ return static_cast<F>(to_underlying(lhs) | to_underlying(rhs));
+}
+
+} // namespace flag_operators
+} // namespace android::ftl