An Implementation of Merge Sort in C

Following C code is the implementation of merge sort, with the time complexity of O(nlogn). It was used in my current project to sort 148 million integers. At first I used bubbled sort, which took me hours to have the 148M integers sorted, because the time
complexity of bubble sort is O(n^2). After replacing the sorting algorithm with merge sort, the time of sorting reduced to less than 10 mins. Amazing improvement! Although I have heard of the importance of sorting/searching algorithm for years, it was the
first time I realize the magic of algorithms.

The merge sort below was found in Internet. Sorry that I forgot to record the hyperlink of the webpage. Only a few changes were made by me.

void Merge(int* input, long p, long r)
{
long mid = floor((p + r) / 2);
long i1 = 0;
long i2 = p;
long i3 = mid + 1;

// Temp array
int* temp=new int[r-p+1];

// Merge in sorted form the 2 arrays
while ( i2 <= mid && i3 <= r )
if ( input[i2] < input[i3] )
temp[i1++] = input[i2++];
else
temp[i1++] = input[i3++];

// Merge the remaining elements in left array
while ( i2 <= mid )
temp[i1++] = input[i2++];

// Merge the remaining elements in right array
while ( i3 <= r )
temp[i1++] = input[i3++];

// Move from temp array to master array
for ( int i = p; i <= r; i++ )
input[i] = temp[i-p];

delete [] temp;
}

// inputs:
//	p - the start index of array input
//	r - the end index of array input
void Merge_sort(int* input, long p, long r)
{
if ( p < r )
{
long mid = floor((p + r) / 2);
Merge_sort(input, p, mid);
Merge_sort(input, mid + 1, r);
Merge(input, p, r);
}
}