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// Copyright 2022 The Dawn & Tint Authors
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#ifndef SRC_TINT_UTILS_CONTAINERS_BITSET_H_
#define SRC_TINT_UTILS_CONTAINERS_BITSET_H_
#include <stdint.h>
#include "src/tint/utils/containers/vector.h"
namespace tint {
/// Bitset is a dynamically sized, vector of bits, packed into integer words.
/// Bits can be individually read and written using the index operator.
///
/// Bitset will fit at least `N` bits internally before spilling to heap allocations.
template <size_t N = 0>
class Bitset {
/// The integer word type used to hold the bits
using Word = size_t;
/// Number of bits per word
static constexpr size_t kWordBits = sizeof(Word) * 8;
/// Number of words required to hold the number of bits
static constexpr size_t NumWords(size_t num_bits) {
return ((num_bits + kWordBits - 1) / kWordBits);
}
public:
/// Constructor
Bitset() = default;
/// Destructor
~Bitset() = default;
/// Accessor for a single bit
struct Bit {
/// The word that contains the bit
Word& word;
/// A word with a single bit set, which masks the targetted bit
Word const mask;
/// Assignment operator
/// @param value the new value for the bit
/// @returns this Bit so calls can be chained
const Bit& operator=(bool value) const {
if (value) {
word = word | mask;
} else {
word = word & ~mask;
}
return *this;
}
/// Conversion operator
/// @returns the bit value
operator bool() const { return (word & mask) != 0; }
};
/// @param new_len the new size of the bitmap, in bits.
void Resize(size_t new_len) {
vec_.Resize(NumWords(new_len));
// Clear any potentially set bits that are in the top part of the word
if (size_t high_bit = new_len % kWordBits; high_bit > 0) {
vec_.Back() &= (static_cast<Word>(1) << high_bit) - 1;
}
len_ = new_len;
}
/// @return the number of bits in the bitset.
size_t Length() const { return len_; }
/// Index operator
/// @param index the index of the bit to access
/// @return the accessor for the indexed bit
Bit operator[](size_t index) {
auto& word = vec_[index / kWordBits];
auto mask = static_cast<Word>(1) << (index % kWordBits);
return Bit{word, mask};
}
/// Const index operator
/// @param index the index of the bit to access
/// @return bool value of the indexed bit
bool operator[](size_t index) const {
const auto& word = vec_[index / kWordBits];
auto mask = static_cast<Word>(1) << (index % kWordBits);
return word & mask;
}
/// @returns true iff the all bits are unset (0)
bool AllBitsZero() const {
for (auto word : vec_) {
if (word) {
return false;
}
}
return true;
}
private:
Vector<size_t, NumWords(N)> vec_;
size_t len_ = 0;
};
} // namespace tint
#endif // SRC_TINT_UTILS_CONTAINERS_BITSET_H_