/* File: tweak_quick.c
   Tweaking Quicksort for better performance
*/

#include <assert.h>
#include <stdio.h>
#include "sorting.h"

index partition(data A[], index low, index high) {
   data x, temp ;
   index i, j ;
   
   i = low - 1;  
   j = high + 1;
   x = A[low] ;
  
   while (1) {
      /* Find an element less than x */
      do {
         j = j - 1;
      } while (A[j] > x) ; 
      
      /* Find an element greater than x */
      do {
         i = i + 1;
      } while (A[i] < x);
                                
      if (i < j) {
         temp = A[j] ;
         A[j] = A[i] ;
         A[i] = temp ;
      } else {
         return j;
      }
    }
}


void quicksort(data A[], index low, index high) {
   index q ;

#ifndef NDEBUG
   printf("Quicksort: low = %d, high = %d\n", low, high) ;   
#endif

   if (high - low <= 15) {
      insertion_sort(A, low, high) ;
      return ;
   }
   
   q = partition(A, low, high) ;
   assert(q < high) ;

   quicksort(A, low, q) ;
   quicksort(A, q + 1, high) ;
}