qtst.c

/*
 * $ cc -O3 -Wall -pedantic -Wextra qtst.c -o qtst
 * $ time ./qtst

     real	0m39,543s
     user	0m37,288s
     sys	0m0,732s
 */

#include <stdio.h>
#include <float.h>
#include <stdlib.h>

#define N 50000000

#define DMIN DBL_MAX
#define DMAX DBL_MIN

static int
cmpfunc(const void *x, const void *y)
{
	double xx = *(double*)x, yy = *(double*)y;
	if (xx < yy) return -1;
	if (xx > yy) return  1;
	return 0;
}

int
main()
{
	size_t i;
	double *arr;

	arr = malloc(N * sizeof(double));
	if (!arr) {
		fprintf(stderr, "Can't allocate memory\n");
		return EXIT_FAILURE;
	}

	for (i=0; i<N; i++) {
		double f = (double)rand() / RAND_MAX;
		/* DMIN + f * (DMAX - DMIN) */ 
		arr[i] = DMIN + f * DMAX - f * DMIN;
	}

	for (i=0; i<10; i++) {
		qsort(arr, N, sizeof(double), cmpfunc);
	}

	free(arr);
	return EXIT_SUCCESS;
}