lib/qsort.c

/*
 * Code adapted from uClibc-0.9.30.3
 *
 * It is therefore covered by the GNU LESSER GENERAL PUBLIC LICENSE
 * Version 2.1, February 1999
 *
 * Wolfgang Denk <wd@denx.de>
 */

/* This code is derived from a public domain shell sort routine by
 * Ray Gardner and found in Bob Stout's snippets collection.  The
 * original code is included below in an #if 0/#endif block.
 *
 * I modified it to avoid the possibility of overflow in the wgap
 * calculation, as well as to reduce the generated code size with
 * bcc and gcc. */

#include <linux/types.h>
#if 0
#include <assert.h>
#else
#define assert(arg)
#endif

void qsort(void  *base,
	   size_t nel,
	   size_t width,
	   int (*comp)(const void *, const void *))
{
	size_t wgap, i, j, k;
	char tmp;

	if ((nel > 1) && (width > 0)) {
		assert(nel <= ((size_t)(-1)) / width); /* check for overflow */
		wgap = 0;
		do {
			wgap = 3 * wgap + 1;
		} while (wgap < (nel-1)/3);
		/* From the above, we know that either wgap == 1 < nel or */
		/* ((wgap-1)/3 < (int) ((nel-1)/3) <= (nel-1)/3 ==> wgap <  nel. */
		wgap *= width;			/* So this can not overflow if wnel doesn't. */
		nel *= width;			/* Convert nel to 'wnel' */
		do {
			i = wgap;
			do {
				j = i;
				do {
					register char *a;
					register char *b;

					j -= wgap;
					a = j + ((char *)base);
					b = a + wgap;
					if ((*comp)(a, b) <= 0) {
						break;
					}
					k = width;
					do {
						tmp = *a;
						*a++ = *b;
						*b++ = tmp;
					} while (--k);
				} while (j >= wgap);
				i += width;
			} while (i < nel);
			wgap = (wgap - width)/3;
		} while (wgap);
	}
}