### 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.

### Reversing char array without splitting the array to tokens

I was reading about strdup, a C++ function and suddenly an idea came to my mind if this can be leveraged to aid in reversing a character array without splitting the array into words and reconstructing it again by placing spaces and removing trailing spaces. Again, I wanted an array to be passed as a function argument and an array size to be passed implicitly with the array to the function. Assumed, a well-formed char array has been passed into the function. No malformed array checking is done inside the function. So, the function signature and definition are like below: Below is the call from the client code to reverse the array without splitting tokens and reconstructing it. Finally, copy the reversed array to the destination.  For GNU C++, we should use strdup instead _strdup . On run, we get the following output: Demo code

### Close a Window Application from another application.

This is just a demo application code to show how the WM_CLOSE message can be sent to the target process which has a titled window to close the application. To achieve this, either we can use SendMessage or PostMessage APIs to send required Windows messages to the target application. Though both the APIs are dispatching WM_XXXXX message to target application two APIs has some differences, these are as below: 1. SendMessage () call is a blocking call but PostMessage is a non-blocking call(Asynchronous) 2. SendMessage() APIs return type is LRESULT (LONG_PTR) but PostMessage() APIs return type is BOOL(typedef int). In Short, SendMessage () APIs return type depends on what message has been sent to the Windowed target process. For the other one, it's always a non-zero value, which indicates the message has been successfully placed on the target process message queue. Now let's see how can I close a target windowed application "Solitaire & Casual Games" from my custom-

### XOR (Exclusive OR) for branchless coding

The following example shows the array reversing using the  XOR operator . No need to take any additional variable to reverse the array.   int main(int argc, _TCHAR* argv[]) { char str[] = "I AM STUDENT"; int length = strlen(str); for(int i = 0; i < ((length/2)); i++) { str[i] ^= str[length - (1+i)]; str[length - (1+i)] ^= str[i]; str[i] ^= str[length - (1+i)]; } cout << str << endl; return 0; } The above example is one of the uses of XOR but XOR comes in handy when we can do branchless coding  methods like butterfly switch etc. Sometimes this is very effective in speeding up the execution.  Let's see one of the uses of XOR in branchless coding. I am taking a simple example of Y = | X |.  Yes, I am generating abs of a supplied number. So, my function signature/definition in C++ looks like below: int absoluteBranch( int x) {     if (x < 0 ) {         return -x;     }     else {         retur