Pow for integral values

Question

I need a version powfor integers. I have 2 problems that I need to solve with pow:

• If the result is larger than my integral type, I need to pinch to numeric_limits::max()
• I need to deal with 41.99999 rounding to 42, not to 41

Does C ++ provide some kind of built-in solution here, or am I forcing to write my own function:

template <typename T>
enable_if_t<is_integral_v<T>, T> mypow(const T base, unsigned int exp) {
    T result = exp == 0U ? base : 1;

    while(exp-- > 1U) {
        if(numeric_limits<T>::max() / result <= base) return numeric_limits<T>::max();
        result *= base;
    }
    return result;
}

Answer 1

Does C ++ provide some kind of built-in solution here

No, the standard library does not have a whole pow.

or i'm stuck writing my own function

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template<class I>
I int_pow_no_overflow(I base, I exp)
{
    double max = std::numeric_limits<I>::max();
    double result = std::round(std::pow(base, exp));
    return result >= max
        ? max
        : result;
}

.

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Answer 2

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#include <type_traits>
#include <iostream>
#include <cmath>
#include <limits>

using namespace std;

template <typename T>
enable_if_t< is_integral<T>::value, T> 
mypow(T base, unsigned int exp) 
{
    T result = T(1);
    bool sign = (base < 0);

    if (sign) base = -base;

    T temp = result;
    while(exp-- != 0) 
    {
        temp *= base;
        if (temp < result)
        {
            return (sign) ? numeric_limits<T>::min() 
                          : numeric_limits<T>::max();
        }
        result = temp;
    }
    return (sign && (exp & 1)) ? -result : result;
}

template <typename T>
enable_if_t< !is_integral<T>::value, int> 
mypow(const T& base, unsigned int exp) 
{
    T result = T(1);
    int i_base = int(floor(base + .5));
    bool sign = (i_base < 0);

    if (sign) i_base = -i_base;

    int temp = result;
    while(exp-- != 0) 
    {
        temp *= i_base;
        if (temp < result)
        {
            return (sign) ? numeric_limits<int>::min() : numeric_limits<int>::max();
        }
        result = temp;
    }
    return (sign && (exp & 1)) ? -result : result;
}

, .

  template<typename T>
   enable_if_t< is_integral<T>::value, T> 
   mypow(T x, unsigned int y) { return T(floor(pow(x, y) + .5)); }

   template<typename T>
   enable_if_t< !is_integral<T>::value, int> 
   mypow(T x, unsigned int y) { return int(floor(pow(floor(x + .5), y) + .5)); }