Why is this an issue?
Since integers are usually represented in binary form in computers, it is efficient to check if a given number is a power of two by checking if its
unsigned representation has a single bit set.
In C++ such check could be expressed as x & (x-1) == 0. However, the intent of this expression is unclear. Furthermore, it
requires to take special care for the value 0, which would pass the above check, while not having any bit set and not being a power of
two.
This check can be expressed more clearly with the std::has_single_bit function template, introduced in C++20.
This rule reports computations that could be replaced with std::has_single_bit .
Noncompliant code example
void f(unsigned x) {
if ((x > 0) && !(x & (x-1))) { // Noncompliant
// Special algorithm for powers of 2
}
// Normal algorithm
}
Compliant solution
void f(unsigned x) {
if (std::has_single_bit(x)) {
// Special algorithm for powers of 2
}
// Normal algorithm
}
