prime_floor

auto eve::prime_floor = functor<prime_floor_t>

inlineconstexpr

Header file

#include <eve/module/combinatorial.hpp>

Callable Signatures

namespace eve
{
   constexpr auto prime_floor(unsigned_value auto x) -> decltype(x) noexcept; //1
   template < integral_value T,  floating_scalar_value U>
   constexpr as_wide_as_t<U, T> prime_floor(T x, as<U>)             noexcept; //2
   template < integral_value T,  unsigned_scalar_value U>
   constexpr as_wide_as_t<U, T> prime_floor(T x, as<U>)             noexcept; //2
}

Parameters

• n: unsigned argument. If n is greater than 104'729, or less than 2 returns 0.

Return value

1. The greatest prime less or equal to n.
2. Same, but the element of the result type is deduced from U.

External references

• Wikipedia: Prime number

Example

// revision 1
#include <eve/module/combinatorial.hpp>
#include <iostream>
 
eve::wide<std::uint32_t> wu([](auto i, auto )->std::uint32_t{ return i;});
eve::wide n{2u, 6u, 6542u, 15u, 1u, 200000u, 10000u, 1000u};
 
int main(){
   std::cout << "<- wu = " << wu << "\n";
   std::cout << "<- n  = " << n << "\n";
 
   std::cout << "-> prime_floor(wu)= " << eve::prime_floor(wu) << "\n";
   std::cout << "-> prime_floor(n) = " << eve::prime_floor(n) << "\n";
   std::cout << "note 0 answer meaning 'out of implemented range'\n";
}