chromium/third_party/grpc/src/src/core/lib/gprpp/bitset.h

// Copyright 2021 gRPC authors.
//
// 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.

#ifndef GRPC_SRC_CORE_LIB_GPRPP_BITSET_H
#define GRPC_SRC_CORE_LIB_GPRPP_BITSET_H

#include <grpc/support/port_platform.h>

#include <stddef.h>
#include <stdint.h>

#include <type_traits>

#include "src/core/lib/gpr/useful.h"

namespace grpc_core {

// Given a bit count as an integer, vend as member type `Type` a type with
// exactly that number of bits. Undefined if that bit count is not available.
template <size_t kBits>
struct UintSelector;

template <>
struct UintSelector<8> { … };
template <>
struct UintSelector<16> { … };
template <>
struct UintSelector<32> { … };
template <>
struct UintSelector<64> { … };

// An unsigned integer of some number of bits.
Uint;

// Given the total number of bits that need to be stored, choose the size of
// 'unit' for a BitSet... We'll use an array of units to store the total set.
// For small bit counts we are selective in the type to try and balance byte
// size and performance
// - the details will likely be tweaked into the future.
// Once we get over 96 bits, we just use uint64_t for everything.
constexpr size_t ChooseUnitBitsForBitSet(size_t total_bits) { … }

// A BitSet that's configurable.
// Contains storage for kTotalBits, stored as an array of integers of size
// kUnitBits. e.g. to store 72 bits in 8 bit chunks, we'd say BitSet<72, 8>.
// Since most users shouldn't care about the size of unit used, we default
// kUnitBits to whatever is selected by ChooseUnitBitsForBitSet
template <size_t kTotalBits,
          size_t kUnitBits = ChooseUnitBitsForBitSet(kTotalBits)>
class BitSet { … };

// Zero-size specialization of BitSet.
// Useful for generic programming.
// Make a compile time error out of get/set type accesses, and hard-codes
// queries that do make sense.
template <>
class BitSet<0> { … };

}  // namespace grpc_core

#endif  // GRPC_SRC_CORE_LIB_GPRPP_BITSET_H