Home >Backend Development >C++ >Why Does `std::pow()` Produce Incorrect Results with Integer Math?

Why Does `std::pow()` Produce Incorrect Results with Integer Math?

Linda Hamilton
Linda HamiltonOriginal
2024-12-26 19:11:10497browse

Why Does `std::pow()` Produce Incorrect Results with Integer Math?

Integer Math with std::pow() Yields Incorrect Results

In the provided code snippet:

int i = 23;
int j = 1;
int base = 10;
int k = 2;
i += j * pow(base, k);
std::cout << i << std::endl;

the expected output should be "123" but instead, "122" is printed.

Reason for Incorrect Output

The issue lies in the use of std::pow(). This function is designed to work with floating-point numbers, which lack infinite precision. Despite this being a potential implementation flaw in g 4.7.2 (MinGW, Windows XP), the root cause is the limited precision of floating-point calculations.

Solution: Integer Power Function

To resolve this issue, an integer power function can be implemented for accurate results with integers. In C 11 and later, this function can be defined as a constexpr, allowing it to potentially compute the result at compile-time if possible:

constexpr int int_pow(int b, int e)
{
    return (e == 0) ? 1 : b * int_pow(b, e - 1);
}

Alternative Tail-Recursive Form

This function can also be implemented in a tail-recursive form, which is more efficient in some circumstances:

constexpr int int_pow(int b, int e, int res = 1)
{
    return (e == 0) ? res : int_pow(b, e - 1, b * res);
}

By using these integer power functions in place of std::pow(), the code will produce the correct output, "123", without the precision issues associated with floating-point calculations.

The above is the detailed content of Why Does `std::pow()` Produce Incorrect Results with Integer Math?. For more information, please follow other related articles on the PHP Chinese website!

Statement:
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn