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// This file is under the public domain.
#pragma once
#include <bit>
#include <cstddef>
#include <initializer_list>
#include <type_traits>
#include "common/common_types.h"
namespace Common {
// Similar to std::bitset, this is a class which encapsulates a bitset, i.e.
// using the set bits of an integer to represent a set of integers. Like that
// class, it acts like an array of bools:
// BitSet32 bs;
// bs[1] = true;
// but also like the underlying integer ([0] = least significant bit):
// BitSet32 bs2 = ...;
// bs = (bs ^ bs2) & BitSet32(0xffff);
// The following additional functionality is provided:
// - Construction using an initializer list.
// BitSet bs { 1, 2, 4, 8 };
// - Efficiently iterating through the set bits:
// for (int i : bs)
// [i is the *index* of a set bit]
// (This uses the appropriate CPU instruction to find the next set bit in one
// operation.)
// - Counting set bits using .Count() - see comment on that method.
template <typename IntTy>
requires std::is_unsigned_v<IntTy>
class BitSet {
public:
// A reference to a particular bit, returned from operator[].
class Ref {
public:
constexpr Ref(Ref&& other) : m_bs(other.m_bs), m_mask(other.m_mask) {}
constexpr Ref(BitSet* bs, IntTy mask) : m_bs(bs), m_mask(mask) {}
constexpr operator bool() const {
return (m_bs->m_val & m_mask) != 0;
}
constexpr bool operator=(bool set) {
m_bs->m_val = (m_bs->m_val & ~m_mask) | (set ? m_mask : 0);
return set;
}
private:
BitSet* m_bs;
IntTy m_mask;
};
// A STL-like iterator is required to be able to use range-based for loops.
class Iterator {
public:
constexpr Iterator(const Iterator& other) : m_val(other.m_val) {}
constexpr Iterator(IntTy val) : m_val(val) {}
constexpr int operator*() {
// This will never be called when m_val == 0, because that would be the end() iterator
return std::countr_zero(m_val);
}
constexpr Iterator& operator++() {
// Unset least significant set bit
m_val &= m_val - IntTy(1);
return *this;
}
constexpr Iterator operator++(int) {
Iterator other(*this);
++*this;
return other;
}
constexpr bool operator==(Iterator other) const {
return m_val == other.m_val;
}
constexpr bool operator!=(Iterator other) const {
return m_val != other.m_val;
}
private:
IntTy m_val;
};
constexpr BitSet() : m_val(0) {}
constexpr explicit BitSet(IntTy val) : m_val(val) {}
constexpr BitSet(std::initializer_list<int> init) {
m_val = 0;
for (int bit : init)
m_val |= (IntTy)1 << bit;
}
constexpr static BitSet AllTrue(std::size_t count) {
return BitSet(count == sizeof(IntTy) * 8 ? ~(IntTy)0 : (((IntTy)1 << count) - 1));
}
constexpr Ref operator[](std::size_t bit) {
return Ref(this, (IntTy)1 << bit);
}
constexpr const Ref operator[](std::size_t bit) const {
return (*const_cast<BitSet*>(this))[bit];
}
constexpr bool operator==(BitSet other) const {
return m_val == other.m_val;
}
constexpr bool operator!=(BitSet other) const {
return m_val != other.m_val;
}
constexpr bool operator<(BitSet other) const {
return m_val < other.m_val;
}
constexpr bool operator>(BitSet other) const {
return m_val > other.m_val;
}
constexpr BitSet operator|(BitSet other) const {
return BitSet(m_val | other.m_val);
}
constexpr BitSet operator&(BitSet other) const {
return BitSet(m_val & other.m_val);
}
constexpr BitSet operator^(BitSet other) const {
return BitSet(m_val ^ other.m_val);
}
constexpr BitSet operator~() const {
return BitSet(~m_val);
}
constexpr BitSet& operator|=(BitSet other) {
return *this = *this | other;
}
constexpr BitSet& operator&=(BitSet other) {
return *this = *this & other;
}
constexpr BitSet& operator^=(BitSet other) {
return *this = *this ^ other;
}
operator u32() = delete;
constexpr operator bool() {
return m_val != 0;
}
constexpr u32 Count() const {
return std::popcount(m_val);
}
constexpr Iterator begin() const {
return Iterator(m_val);
}
constexpr Iterator end() const {
return Iterator(0);
}
IntTy m_val;
};
} // namespace Common
typedef Common::BitSet<u8> BitSet8;
typedef Common::BitSet<u16> BitSet16;
typedef Common::BitSet<u32> BitSet32;
typedef Common::BitSet<u64> BitSet64;
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