Как я применял Сито из Eratosthenes У меня возникла проблема с std::vector<bool>
: нет доступа к исходным данным.Почему std :: vector <bool> быстрее?
Итак, я решил использовать пользовательскую минималистическую реализацию, где у меня был бы доступ к указателю данных.
#ifndef LIB_BITS_T_H
#define LIB_BITS_T_H
#include <algorithm>
template <typename B>
class bits_t{
public:
typedef B block_t;
static const size_t block_size = sizeof(block_t) * 8;
block_t* data;
size_t size;
size_t blocks;
class bit_ref{
public:
block_t* const block;
const block_t mask;
bit_ref(block_t& block, const block_t mask) noexcept : block(&block), mask(mask){}
inline void operator=(bool v) const noexcept{
if(v) *block |= mask;
else *block &= ~mask;
}
inline operator bool() const noexcept{
return (bool)(*block & mask);
}
};
bits_t() noexcept : data(nullptr){}
void resize(const size_t n, const bool v) noexcept{
block_t fill = v ? ~block_t(0) : block_t(0);
size = n;
blocks = (n + block_size - 1)/block_size;
data = new block_t[blocks];
std::fill(data, data + blocks, fill);
}
inline block_t& block_at_index(const size_t i) const noexcept{
return data[i/block_size];
}
inline size_t index_in_block(const size_t i) const noexcept{
return i % block_size;
}
inline bit_ref operator[](const size_t i) noexcept{
return bit_ref(block_at_index(i), block_t(1) << index_in_block(i));
}
~bits_t(){
delete[] data;
}
};
#endif // LIB_BITS_T_H
Код почти такой же, чем в /usr/include/c++/4.7/bits/stl_bvector.h, но медленнее.
Я попробовал оптимизацию,
#ifndef LIB_BITS_T_H
#define LIB_BITS_T_H
#include <algorithm>
template <typename B>
class bits_t{
const B mask[64] = {
0b0000000000000000000000000000000000000000000000000000000000000001,
0b0000000000000000000000000000000000000000000000000000000000000010,
0b0000000000000000000000000000000000000000000000000000000000000100,
0b0000000000000000000000000000000000000000000000000000000000001000,
0b0000000000000000000000000000000000000000000000000000000000010000,
0b0000000000000000000000000000000000000000000000000000000000100000,
0b0000000000000000000000000000000000000000000000000000000001000000,
0b0000000000000000000000000000000000000000000000000000000010000000,
0b0000000000000000000000000000000000000000000000000000000100000000,
0b0000000000000000000000000000000000000000000000000000001000000000,
0b0000000000000000000000000000000000000000000000000000010000000000,
0b0000000000000000000000000000000000000000000000000000100000000000,
0b0000000000000000000000000000000000000000000000000001000000000000,
0b0000000000000000000000000000000000000000000000000010000000000000,
0b0000000000000000000000000000000000000000000000000100000000000000,
0b0000000000000000000000000000000000000000000000001000000000000000,
0b0000000000000000000000000000000000000000000000010000000000000000,
0b0000000000000000000000000000000000000000000000100000000000000000,
0b0000000000000000000000000000000000000000000001000000000000000000,
0b0000000000000000000000000000000000000000000010000000000000000000,
0b0000000000000000000000000000000000000000000100000000000000000000,
0b0000000000000000000000000000000000000000001000000000000000000000,
0b0000000000000000000000000000000000000000010000000000000000000000,
0b0000000000000000000000000000000000000000100000000000000000000000,
0b0000000000000000000000000000000000000001000000000000000000000000,
0b0000000000000000000000000000000000000010000000000000000000000000,
0b0000000000000000000000000000000000000100000000000000000000000000,
0b0000000000000000000000000000000000001000000000000000000000000000,
0b0000000000000000000000000000000000010000000000000000000000000000,
0b0000000000000000000000000000000000100000000000000000000000000000,
0b0000000000000000000000000000000001000000000000000000000000000000,
0b0000000000000000000000000000000010000000000000000000000000000000,
0b0000000000000000000000000000000100000000000000000000000000000000,
0b0000000000000000000000000000001000000000000000000000000000000000,
0b0000000000000000000000000000010000000000000000000000000000000000,
0b0000000000000000000000000000100000000000000000000000000000000000,
0b0000000000000000000000000001000000000000000000000000000000000000,
0b0000000000000000000000000010000000000000000000000000000000000000,
0b0000000000000000000000000100000000000000000000000000000000000000,
0b0000000000000000000000001000000000000000000000000000000000000000,
0b0000000000000000000000010000000000000000000000000000000000000000,
0b0000000000000000000000100000000000000000000000000000000000000000,
0b0000000000000000000001000000000000000000000000000000000000000000,
0b0000000000000000000010000000000000000000000000000000000000000000,
0b0000000000000000000100000000000000000000000000000000000000000000,
0b0000000000000000001000000000000000000000000000000000000000000000,
0b0000000000000000010000000000000000000000000000000000000000000000,
0b0000000000000000100000000000000000000000000000000000000000000000,
0b0000000000000001000000000000000000000000000000000000000000000000,
0b0000000000000010000000000000000000000000000000000000000000000000,
0b0000000000000100000000000000000000000000000000000000000000000000,
0b0000000000001000000000000000000000000000000000000000000000000000,
0b0000000000010000000000000000000000000000000000000000000000000000,
0b0000000000100000000000000000000000000000000000000000000000000000,
0b0000000001000000000000000000000000000000000000000000000000000000,
0b0000000010000000000000000000000000000000000000000000000000000000,
0b0000000100000000000000000000000000000000000000000000000000000000,
0b0000001000000000000000000000000000000000000000000000000000000000,
0b0000010000000000000000000000000000000000000000000000000000000000,
0b0000100000000000000000000000000000000000000000000000000000000000,
0b0001000000000000000000000000000000000000000000000000000000000000,
0b0010000000000000000000000000000000000000000000000000000000000000,
0b0100000000000000000000000000000000000000000000000000000000000000,
0b1000000000000000000000000000000000000000000000000000000000000000
};
public:
typedef B block_t;
static const size_t block_size = sizeof(block_t) * 8;
block_t* data;
size_t size;
size_t blocks;
class bit_ref{
public:
block_t* const block;
const block_t mask;
bit_ref(block_t& block, const block_t mask) noexcept : block(&block), mask(mask){}
inline void operator=(bool v) const noexcept{
if(v) *block |= mask;
else *block &= ~mask;
}
inline operator bool() const noexcept{
return (bool)(*block & mask);
}
};
bits_t() noexcept : data(nullptr){}
void resize(const size_t n, const bool v) noexcept{
block_t fill = v ? ~block_t(0) : block_t(0);
size = n;
blocks = (n + block_size - 1)/block_size;
data = new block_t[blocks];
std::fill(data, data + blocks, fill);
}
inline block_t& block_at_index(const size_t i) const noexcept{
return data[i/block_size];
}
inline size_t index_in_block(const size_t i) const noexcept{
return i % block_size;
}
inline bit_ref operator[](const size_t i) noexcept{
return bit_ref(block_at_index(i), mask[index_in_block(i)]);
}
~bits_t(){
delete[] data;
}
};
#endif // LIB_BITS_T_H
(Компиляция с г ++ 4,7 -O3)
Эратосфен алгоритм решета (33.333.333 бит)
std::vector<bool>
19.1s
bits_t<size_t>
19.9s
bits_t<size_t> (with lookup table)
19.7s
т е р + размер (33.333.333 бит) + dtor
std::vector<bool>
120 мс
bits_t<size_t>
150мс
ВОПРОС: Где замедление происходят из ?
«_The код ** ** почти то же самое, чем в /usr/include/c++/4.7/bits/stl_bvector.h_» –
Предположительно компилятором разрешено использовать тот факт, что 'stl_bvector. h' является частью реализации, позволяя ему делать специальные оптимизации. –
'resize' немного страшно - он не сохраняет старые данные и утечки старого выделения. Вы также получили недействительную семантику копирования. –