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 arrayint* temp=new int[r-p+1];// Merge in sorted form the 2 arrayswhile ( i2 <= mid && i3 <= r )if ( input[i2] < input[i3] )temp[i1++] = input[i2++];elsetemp[i1++] = input[i3++];// Merge the remaining elements in left arraywhile ( i2 <= mid )temp[i1++] = input[i2++];// Merge the remaining elements in right arraywhile ( i3 <= r )temp[i1++] = input[i3++];// Move from temp array to master arrayfor ( 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 inputvoid 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);}}