/* ECP: FILEname=fig11_23.c */
/* 1*/   #define SwapElements( i, j ) \
/* 2*/       {  ElementType Tmp = A[ i ]; A[ i ] = A[ j ]; A[ j ] = Tmp; }

/* 3*/   static int
/* 4*/   Partition( ElementType A[ ], int Low, int High )
/* 5*/   {
/* 6*/       int Center = ( Low + High ) / 2;
/* 7*/       const ElementType Pivot = A[ Center ];
/* 8*/       int i = Low - 1, j = High;

/* 9*/       SwapElements( Center, High );
/*10*/       for( ; ; )
/*11*/       {
/*12*/           while( A[ ++i ] < Pivot )   /* Find A "large" Element */
/*13*/               ;                       /* i < High Is Guaranteed */ 
/*14*/           while( A[ --j ] > Pivot )   /* Find A "small" Element */
/*15*/               if( j == 0 )            /* Don't run off the end! */
/*16*/                   break;

/*17*/           if( i >= j )
/*18*/               break;

/*19*/           /* Invariant: i < j, A[ i ] >= Pivot, A[ j ] <= Pivot */
/*20*/           SwapElements( i, j );
/*21*/       }
/*22*/       SwapElements( i, High );

/*23*/       return i;
/*24*/   }