#include <stdio.h>
#include <malloc.h>
#include "gene.h"
#include "ga_random.h"


/***************************************************************************
 * FUNCTION: red_surrogate_cross
 *
 * DESCRIBE: Performs a 2 point, reduced surrogate form of crossover
 *           on two (parent) rules to form two new (child) rules.  
 *
 *           Reduced Surrogate crossover first identifies all positions
 *           in which the parent strings differ. Crossover points are 
 *           only allowed to occur in these positions.
 *
 * INPUT PARAMETERS: Two gene strings;
 *                   The length of these strings;
 *
 * RETURN VALUE: number of bits which differ in 2 input buffers
 *
 * RESULT: The two input arrays are filled with the children of
 *         crossover (if crossover occured)
 *
 * CALLS:
 *	(ga_random.h) randomain
 ****************************************************************************/
int
red_surrogate_cross ( buf1, buf2, length )
GENE_DATA             buf1[], buf2[];
int                   length;
{
 static char first_time = 1;	/* Flag for first time in this routine */
 static int *diff;		        /* Array of differing positions */
 int xpoint1;		            /* Index into diff of 1st crossover point */
 int xpoint2;		            /* Index into diff of 2nd crossover point */
 int xtemp;            	        /* Temporary for swap of xpoints */
 GENE_DATA temp;	            /* Temporary for swap of parent material */
 int numdiff;		            /* Number of differing positions */
 int i;                         

 if (first_time) 
    {
    diff = (int *) malloc ( length * sizeof(int) );
    first_time = 0;
    }

/* Find all differing positions */

 numdiff = 0;
 for (i=0; i < length; i++) 
     if (buf1[i] != buf2[i]) 
        diff[numdiff++] = i;

/*
 * If there is only one difference between parents,
 * a cross will only result in a duplicate...
 * so don't bother
 */

 if (numdiff <= 1)
    return (numdiff);


/*
 * Note that after crossover,
 * buf1 & buf2 will instead contain children 
 */

#define swap(X)	{   temp  = buf1[X]; \
		          buf1[X] = buf2[X]; \
	              buf2[X] = temp; }



/* Select two crossover indices into diff */

 xpoint1 =  randomain ( numdiff-1, 0 );
 xpoint2 =  randomain ( numdiff-1, 0 );




 /* make sure xpoint1 is less than xpoint2 */

 if (xpoint2 < xpoint1) 
    {
       xtemp = xpoint1;
     xpoint1 = xpoint2; 
     xpoint2 = xtemp;
    }

 /* careful not to alter xpoint out of array bounds */
 else
 if (xpoint2 == xpoint1)
	{ if (xpoint1==0)
	      xpoint2 = 1;
      else
	      xpoint1--;
    }

 else
 /* xpoint1 < xpoint2 */
     ;




/* Crossover; we'll try to exchange the smaller set of chromosomes */

 /* between crossover points, inclusive */
 if ( numdiff > 2*((xpoint2 - xpoint1)+1) ) 
	{
     for (i=xpoint1; i <= xpoint2; i++)
	     swap(diff[i]);
    }
 /* outside of crossover points, inclusive */
 else 
    {
     for (i=0; i <= xpoint1; i++)
	     swap( diff[i] );
     for (i=xpoint2; i < numdiff; i++)
	     swap( diff[i] );
    }

 return (numdiff); 
}