include/llvm/ADT/Bitset.h

//=== llvm/ADT/Bitset.h - constexpr std::bitset -----------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Defines a std::bitset like container that can be used in constexprs.
// That constructor and many of the methods are constexpr. std::bitset doesn't
// get constexpr methods until C++23. This class also provides a constexpr
// constructor that accepts an initializer_list of bits to set.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_BITSET_H
#define LLVM_ADT_BITSET_H

#include <llvm/ADT/STLExtras.h>
#include <array>
#include <climits>
#include <cstdint>

namespace llvm {

/// This is a constexpr reimplementation of a subset of std::bitset. It would be
/// nice to use std::bitset directly, but it doesn't support constant
/// initialization.
template <unsigned NumBits>
class Bitset {
  typedef uintptr_t BitWord;

  enum { BITWORD_SIZE = (unsigned)sizeof(BitWord) * CHAR_BIT };

  static_assert(BITWORD_SIZE == 64 || BITWORD_SIZE == 32,
                "Unsupported word size");

  static constexpr unsigned NumWords = (NumBits + BITWORD_SIZE-1) / BITWORD_SIZE;
  std::array<BitWord, NumWords> Bits{};

protected:
  constexpr Bitset(const std::array<BitWord, NumWords> &B)
      : Bits{B} {}

public:
  constexpr Bitset() = default;
  constexpr Bitset(std::initializer_list<unsigned> Init) {
    for (auto I : Init)
      set(I);
  }

  Bitset &set() {
    std::fill(std::begin(Bits), std::end(Bits), -BitWord(0));
    return *this;
  }

  constexpr Bitset &set(unsigned I) {
    Bits[I / BITWORD_SIZE] |= BitWord(1) << (I % BITWORD_SIZE);
    return *this;
  }

  constexpr Bitset &reset(unsigned I) {
    Bits[I / BITWORD_SIZE] &= ~(BitWord(1) << (I % BITWORD_SIZE));
    return *this;
  }

  constexpr Bitset &flip(unsigned I) {
    Bits[I / BITWORD_SIZE] ^= BitWord(1) << (I % BITWORD_SIZE);
    return *this;
  }

  constexpr bool operator[](unsigned I) const {
    BitWord Mask = BitWord(1) << (I % BITWORD_SIZE);
    return (Bits[I / BITWORD_SIZE] & Mask) != 0;
  }

  constexpr bool test(unsigned I) const { return (*this)[I]; }

  constexpr size_t size() const { return NumBits; }

  bool any() const {
    return llvm::any_of(Bits, [](BitWord I) { return I != 0; });
  }
  bool none() const { return !any(); }
  size_t count() const {
    size_t Count = 0;
    for (auto B : Bits)
      Count += llvm::popcount(B);
    return Count;
  }

  constexpr Bitset &operator^=(const Bitset &RHS) {
    for (unsigned I = 0, E = Bits.size(); I != E; ++I) {
      Bits[I] ^= RHS.Bits[I];
    }
    return *this;
  }
  constexpr Bitset operator^(const Bitset &RHS) const {
    Bitset Result = *this;
    Result ^= RHS;
    return Result;
  }

  constexpr Bitset &operator&=(const Bitset &RHS) {
    for (unsigned I = 0, E = Bits.size(); I != E; ++I)
      Bits[I] &= RHS.Bits[I];
    return *this;
  }
  constexpr Bitset operator&(const Bitset &RHS) const {
    Bitset Result = *this;
    Result &= RHS;
    return Result;
  }

  constexpr Bitset &operator|=(const Bitset &RHS) {
    for (unsigned I = 0, E = Bits.size(); I != E; ++I) {
      Bits[I] |= RHS.Bits[I];
    }
    return *this;
  }
  constexpr Bitset operator|(const Bitset &RHS) const {
    Bitset Result = *this;
    Result |= RHS;
    return Result;
  }

  constexpr Bitset operator~() const {
    Bitset Result = *this;
    for (auto &B : Result.Bits)
      B = ~B;
    return Result;
  }

  bool operator==(const Bitset &RHS) const {
    return std::equal(std::begin(Bits), std::end(Bits), std::begin(RHS.Bits));
  }

  bool operator!=(const Bitset &RHS) const { return !(*this == RHS); }

  bool operator < (const Bitset &Other) const {
    for (unsigned I = 0, E = size(); I != E; ++I) {
      bool LHS = test(I), RHS = Other.test(I);
      if (LHS != RHS)
        return LHS < RHS;
    }
    return false;
  }
};

} // end namespace llvm

#endif