Compile-Time

constexpr Prime Sieve

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Asked at Maven Securities

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xxxxxx xxxxxx xxxx xxxxx xxxxxx xx xxx xxxxxxx xxxxxxx xxxxxxxxxxxxxx: xxxx xxxx xxxx xxx xxxxxx xxx xxx xxx xxxxxxxx xx xxx xxxxxxxxxx. xxx xxxxx xx xxxxxxxxxxxx xx xxx xxxxxxx xxxxx xxx xxxx, xxxxx xxxxxx xx xxxxx xx xx xxxxxxxxx, xxx xxxxxx xx xxxxxx xxx x++xx xxxxxxxx xxxxxxxxxx xxxxxxxx xxxxxxx.

xxxxxxxxx xxx xxxxxxxx xxxxxxxxx:

xxxxx_xxxxxx_xxxxx<x>(): x xxxxxxxxx xxx::xxxx_x, xxx xxxxxx xx xxxxxx xxxxxxxx xxxx xxxx x.
xxxxxx_xxxxx<x>(): x xxxxxxxxx xxxxxxxx xxxxxxxxx xxx::xxxxx<xxxx xxxx, xxxxx_xxxxxx_xxxxx<x>()> xxxxxxx xxxxxxx xxxxx xxxxxx xx xxxxxxxxx xxxxx. xxxx xxx xxxxxx xxxx: xxx xxxxx xx xxxxx xx x xxxxxxx-xxxx xxxx xx xxxx xxx xxxxxxxx xxxxxxxx, xxxxx xx xxx xxx xxxxx xxxxx xxxxx xxx xxxx xx xxxxxxxxx xxxx xxx xxxxx (xxx xxxxxxxx xxxxx xxxx xx).

xxxx xxxx xxxx xx xxxxxxxx xxxxxxxxxxx (x xxxxxx xxxx xxxxxxxxxxx x xxxxxxxxx xxxxxxxx xxxx xxxxxx_xxxxx<xxxx>(), xxx xxx xxxxxxxxx xxxxxxxx xxxxxxx xxxxxx_xxxxxxx) xxx xx xxxxx xxxxxxx xxxxx: xxx xxxxxxx xxxxxx xxxx xxxxxxxxx xxxxx_xxxxxx_xxxxx<xxxxxx>() xx xxxxxxx, xxxxx xx xxxxxxxx-xxxxxxxxxx xxxx xxxxxx xxxxx.

xxxxxxxx

[]{ xxxx x = xxxxxx_xxxxx<xx>(); xxxxxx xxx::xxxxxx<xxxx xxxx>(x.xxxxx(), x.xxx()); }()
// [x, x, x, x, xx, xx, xx, xx, xx, xx]

xxxxxx_xxxx<xxxx xxxx>(xxxxx_xxxxxx_xxxxx<xxx>())
// xx

xxxxxxxxxxx

(x xx x xx xxxxxx). xxxxxx_xxxxx<x>() xx xxxxxxxxxxxx xx xx (x = xxxxx); xxx xxxxx xxxxx xx xxxxx xxx xx xx (x = xxxxxx).
xxx xx xxxxxx xxxxx: xxxxx xxxxxxxx xxx xxxxxxxxx xx xxx xxxx xxxxxx xxx xxxxxxxx'x xxxxxxxx xxxxxxxxx xxx xxx (x = xxxx) xxxxxxxxx xxxx xxx xxxxxxxxxx xxxx xx xxxxxxx.
xx xxxxxxxxxx xxxxxx xxxxxx xxxxxx: x xxxxx xxx::xxxxx<xxxx, x> xx xxxxx xx xxxx xx xxxxxxxx xxxxxxxxxx xx xxxxx xxxxx.
xxxxx_xxxxxx_xxxxx<x>() == x xxx xxxxxx_xxxxx<x>() xx xx xxxxx xxxxx; xxxx xxxx xxxxxxx.

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Language: C++primes_below

#include <array>
#include <cstddef>

// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...

template <std::size_t N>
constexpr std::size_t count_primes_below() {
    // ...
    return 0;
}

template <std::size_t N>
constexpr std::array<long long, count_primes_below<N>()> primes_below() {
    std::array<long long, count_primes_below<N>()> primes{};
    // ...
    return primes;
}

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