绑定自下而上合并排序

Question

以下代码来自：http://www.geeksforgeeks.org/iterative-merge-sort/

/* Iterative mergesort function to sort arr[0...n-1] */
void mergeSort(int arr[], int n)
{
   int curr_size;  // For current size of subarrays to be merged
                   // curr_size varies from 1 to n/2
   int left_start; // For picking starting index of left subarray
                   // to be merged

   // Merge subarrays in bottom up manner.  First merge subarrays of
   // size 1 to create sorted subarrays of size 2, then merge subarrays
   // of size 2 to create sorted subarrays of size 4, and so on.
   for (curr_size=1; curr_size<=n-1; curr_size = 2*curr_size)
   {
       // Pick starting point of different subarrays of current size
       for (left_start=0; left_start<n-1; left_start += 2*curr_size)
       {
           // Find ending point of left subarray. mid+1 is starting 
           // point of right
           int mid = left_start + curr_size - 1;

           int right_end = min(left_start + 2*curr_size - 1, n-1);

           // Merge Subarrays arr[left_start...mid] & arr[mid+1...right_end]
           merge(arr, left_start, mid, right_end);
       }
   }
}

我不明白为什么right_end应该在（n-1）之间取（left_start + 2 * curr_size - 1）的min。

我认为right_end应该是left_start + 2 * curr_size - 1而不是n-1。