Skip to main content

Power of Two

 In this post will be discussing how to calculate if a number is a power of two or not. As an example, 8 is a power of two but the number 10 is not.

There are many ways we can solve this.

First, we will take an approach which is simple and iterative. In this case, we will calculate the power of two one by one and check with the supplied number. The below code illustrates it.

bool isPowerofTwo(unsigned num)
{
auto y = 1;
while (0 != y)
{
if (num == y) return true;
if (num < y) return false;
y <<= 1;
}

return false;
}

Second, assuming, the number is a 32-bit number, this is also an iterative solution. In this scenario, iterating all bits and counting the set bits. Any number which is a power of 2 will have only one bit set and the rest will be zeros. As an example, 8 in binary representation is 1000. Using this observation, we can implement an iterative solution.

bool isPowerofTwo(unsigned num)
{
auto one_count = 0;
for (auto index = 0; index < 32; ++index) {
if ( num & 1) ++one_count;
num >>= 1;
}
return one_count == 1;
}

So, from the client code, the above code returns true for the number 8388608.
std::cout << "Is 8,388,608 power of two? Ans:- " << std::boolalpha << isPowerofTwo(8388608) << "\n";

Though the above solution works, however, both solutions are not efficient as it's looping through.

So, we can use a trick, as we know if a number is a power of two, in that case, only one bit will be set. Hence, here is the third solution and it's the most optimized one:

bool isPowerOfTwo(unsigned num) 
{
       return (num & (num - 1)) == 0;
}

Let the number be 8 and its bit representation is 1000 and (num - 1) = 7. 7's bit representation is 0111. The bitwise '&' result is 0000 = 0. Hence, 8 is a power of two.


Labels:

Comments

Post a Comment

Popular posts from this blog

A simple approach to generate Fibonacci series via multi-threading

T his is a very simple approach taken to generate the Fibonacci series through multithreading. Here instead of a function, used a function object. The code is very simple and self-explanatory.  #include <iostream> #include <mutex> #include <thread> class Fib { public:     Fib() : _num0(1), _num1(1) {}     unsigned long operator()(); private:     unsigned long _num0, _num1;     std::mutex mu; }; unsigned long Fib::operator()() {     mu.lock(); // critical section, exclusive access to the below code by locking the mutex     unsigned long  temp = _num0;     _num0 = _num1;     _num1 = temp + _num0;     mu.unlock();     return temp; } int main() {     Fib f;          int i = 0;     unsigned long res = 0, res2= 0, res3 = 0;     std::cout << "Fibonacci series: ";     while (i <= 15) {         std::thread t1([&] { res = f(); }); // Capturing result to respective variable via lambda         std::thread t2([&] { res2 = f(); });         std::thread t3(
Post a Comment
Read more

Variadic template class to add numbers recursively during compilation

 The idea of having a class to add numbers (variable parameters) during compilation time recursively. Also wanted to restrict types to a single type while sending parameters to class member function. That said, if we mix int, float and double types to add function shall result in compilation error. How do we achieve this. The below is the code which actually helps to achieve this: <code> #include < fmt/format.h > template < typename T> class MyVarSumClass{     private :         T _sum = 0 ;     public :         template < typename ... TRest>         T add(T num, TRest... nums){             static_assert (std::conjunction<std::is_same<TRest, T>...>{}); /* Assert fails                if types are different */             _sum += num;             return add(nums...); // Next parameter packs gets picked recursively         }         // Base case         T add(T num){             _sum += num;             return _sum;         } }; int main() {     My
Post a Comment
Read more

A concept to a product (Kimidori [ 黄緑]) - Part 2

In the previous part , we have seen KIMIDORI [ 黄緑] detect if a URL is malicious. In this part, we will see the details that KIMIDORI [ 黄緑] fetches out of the URL provided. As an example, provided a safe URL, https://www.azuresys.com/, and let's see what it brings out: As we can see, the link is safe and the link is active, which means we can just click on the link to open it on IE.  Now it's time to look into the URL report (still under development):  We have URLs IP, Location, and HTTP Status code. The Report part is a sliding window, the Show Report button shows as well as hides the report. Show / Hide Report is a toggle button. Let's see if we get the same details for any bad (phishing / malicious) URL: Took an URL example from a phishing link and tested it. The tool detected it as not a good link (Screen Shot Below) & link does not activate unlike a safe URL: Now let's see the report part for more details including domain registration details: It looks like it&
Post a Comment
Read more