SingleSource/Benchmarks/Shootout/heapsort.c

/* -*- mode: c -*-
 * $Id$
 * http://www.bagley.org/~doug/shootout/
 */

#include <stdlib.h>
#include <math.h>
#include <stdio.h>
#define heapsort benchmark_heapsort

#define IM 139968
#define IA   3877
#define IC  29573

double
gen_random(double max) {
    static long last = 42;
    return( max * (last = (last * IA + IC) % IM) / IM );
}

void
heapsort(int n, double *ra) {
    int i, j;
    int ir = n;
    int l = (n >> 1) + 1;
    double rra;

    for (;;) {
	if (l > 1) {
	    rra = ra[--l];
	} else {
            rra = ra[ir];
	    ra[ir] = ra[1];
	    if (--ir == 1) {
		ra[1] = rra;
		return;
	    }
	}

	i = l;
	j = l << 1;
	while (j <= ir) {
	    if (j < ir && ra[j] < ra[j+1]) { 
              ++j; 
            }
	    if (rra < ra[j]) {
		ra[i] = ra[j];
		j += (i = j);
	    } else {
		j = ir + 1;
	    }
	}
	ra[i] = rra;
    }
}

int
main(int argc, char *argv[]) {
#ifdef SMALL_PROBLEM_SIZE
#define LENGTH 800000
#else
#define LENGTH 8000000
#endif
    int N = ((argc == 2) ? atoi(argv[1]) : LENGTH);
    double *ary;
    int i;
    
    /* create an array of N random doubles */
    ary = (double *)malloc((N+1) * sizeof(double));
    for (i=1; i<=N; i++) {
	ary[i] = gen_random(1);
    }

    heapsort(N, ary);

    printf("%f\n", ary[N]);

    free(ary);
    return(0);
}