Use std::bitset to implement EnumBitSet

Summary: This diff changes EnumBitSet to use `std::bitset` internally, which means we are not restricted to 64 enum values anymore.

Reviewed By: arnaudvenet

Differential Revision: D51668589

fbshipit-source-id: 614f35f489eb7e925dbc9739c562f4d9641e4ad3

include/sparta/utils/EnumBitSet.h

@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <cstdint>
+#include <bitset>
 #include <initializer_list>
 #include <type_traits>
 
@@ -19,7 +19,7 @@ namespace sparta {
  * `EnumBitSet<Enum>` can be used to store an OR-combination of enum values,
  * where `Enum` is an enum class type.
  *
- * `Enum` underlying values must be unsigned integers between 0 and 63. `Enum`
+ * `Enum` underlying values must be unsigned integers. `Enum`
  * must have a `_Count` member containing the maximum value.
  */
 template <typename Enum>
@@ -29,36 +29,33 @@ class EnumBitSet final {
   static_assert(
       std::is_unsigned_v<std::underlying_type_t<Enum>>,
       "The underlying type of Enum must be an unsigned arithmetic type");
-  static_assert(static_cast<std::underlying_type_t<Enum>>(Enum::_Count) < 64u,
-                "Enum::_Count must be less than 64");
+  static_assert(static_cast<std::underlying_type_t<Enum>>(Enum::_Count) >= 0,
+                "Enum::_Count must contain the maximum value");
+  static_assert(
+      static_cast<std::underlying_type_t<Enum>>(Enum::_Count) < 512u,
+      "Enum::_Count is too large, consider using a sparse set instead");
 
  public:
   using EnumType = Enum;
   using EnumUnderlyingT = std::underlying_type_t<Enum>;
 
  private:
-  using IntT = std::conditional_t<
-      static_cast<EnumUnderlyingT>(Enum::_Count) < 8u,
-      std::uint8_t,
-      std::conditional_t<static_cast<EnumUnderlyingT>(Enum::_Count) < 32u,
-                         std::uint32_t,
-                         std::uint64_t>>;
+  using BitSetT = std::bitset<static_cast<EnumUnderlyingT>(Enum::_Count) + 1>;
 
-  static constexpr IntT enum_to_bit(Enum value) {
-    return static_cast<IntT>(1)
-           << static_cast<IntT>(static_cast<EnumUnderlyingT>(value));
+  static constexpr BitSetT enum_to_bit(Enum value) {
+    return BitSetT{}.set(static_cast<EnumUnderlyingT>(value), true);
   }
 
  public:
   EnumBitSet() = default;
 
   /* implicit */ constexpr EnumBitSet(Enum value)
-      : value_(enum_to_bit(value)) {}
+      : value_{enum_to_bit(value)} {}
 
   /* implicit */ constexpr EnumBitSet(std::initializer_list<Enum> set)
-      : value_(0u) {
+      : value_{} {
     for (auto value : set) {
-      value_ |= enum_to_bit(value);
+      value_.set(static_cast<EnumUnderlyingT>(value), true);
     }
   }
 
@@ -118,48 +115,38 @@ class EnumBitSet final {
 
   constexpr EnumBitSet operator~() const { return EnumBitSet(~value_); }
 
-  explicit constexpr operator bool() const { return value_ != 0; }
+  explicit operator bool() const { return value_.any(); }
 
-  constexpr bool operator!() const { return value_ == 0; }
+  bool operator!() const { return value_.none(); }
 
-  constexpr bool operator==(EnumBitSet set) const {
-    return value_ == set.value_;
-  }
+  bool operator==(const EnumBitSet& set) const { return value_ == set.value_; }
 
-  constexpr bool operator!=(EnumBitSet set) const {
-    return value_ != set.value_;
-  }
+  bool operator!=(EnumBitSet set) const { return value_ != set.value_; }
 
-  constexpr bool test(Enum value) const {
-    return (value_ & enum_to_bit(value)) == enum_to_bit(value);
+  bool test(Enum value) const {
+    return value_[static_cast<EnumUnderlyingT>(value)];
   }
 
   constexpr EnumBitSet& set(Enum value, bool on = true) {
-    if (on) {
-      value_ |= enum_to_bit(value);
-    } else {
-      value_ &= ~enum_to_bit(value);
-    }
+    value_.set(static_cast<EnumUnderlyingT>(value), on);
     return *this;
   }
 
-  constexpr bool empty() const { return value_ == 0; }
+  bool empty() const { return value_.none(); }
 
-  constexpr void clear() { value_ = 0; }
+  constexpr void clear() { value_.reset(); }
 
-  constexpr bool is_subset_of(EnumBitSet set) const {
+  bool is_subset_of(EnumBitSet set) const {
     return (value_ | set.value_) == set.value_;
   }
 
-  constexpr bool has_single_bit() const {
-    return (value_ && !(value_ & (value_ - 1)));
-  }
+  bool has_single_bit() const { return value_.count() == 1; }
 
  private:
-  explicit constexpr EnumBitSet(IntT value) : value_(value) {}
+  explicit constexpr EnumBitSet(BitSetT value) : value_(std::move(value)) {}
 
  private:
-  IntT value_ = 0;
+  BitSetT value_ = 0;
 };
 
 } // namespace sparta