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Round an integer up to the closest 2's power.
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#include <limits> | |
#include <type_traits> | |
template <int bit> | |
struct or_shift | |
{ | |
template <typename Int> | |
static constexpr auto apply(Int n) -> Int | |
{ | |
return or_shift<bit / 2>::apply(n | (n >> bit)); | |
} | |
}; | |
template <> | |
struct or_shift<1> | |
{ | |
template <typename Int> | |
static constexpr auto apply(Int n) -> Int | |
{ | |
return n | (n >> 1); | |
} | |
}; | |
template <typename Int, typename R = typename std::make_unsigned<Int>::type> | |
constexpr auto pow2_roundup(Int n) -> R | |
{ | |
return or_shift< | |
std::numeric_limits<R>::digits / 2>::apply(R(n) - 1) + 1; | |
} | |
#include <iostream> | |
#include <iomanip> | |
int main() | |
{ | |
using namespace std; | |
cout | |
<< "0\t" << pow2_roundup(0) << endl | |
<< "1\t" << pow2_roundup(1) << endl | |
<< "2\t" << pow2_roundup(2) << endl | |
<< "3\t" << pow2_roundup(3) << endl | |
<< "143\t" << pow2_roundup(143) << endl | |
<< "max\t" << pow2_roundup(numeric_limits<int>::max()) << endl; | |
} |
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