nqsort.c

Arithmetic coding source code. A very good software for arithmetic coding.

/*
 * Copyright (c) 1992 The Regents of the University of California.
 * All rights reserved.
 *
 */

/*
 * Qsort routine from J. Bentley & M. D. McIlroy's "Engineering a Sort Function".
 */
#define swapcode(TYPE, parmi, parmj, n) { \
	long i = (n) / sizeof (TYPE); \
	register TYPE *pi = (TYPE *) (parmi); \
	register TYPE *pj = (TYPE *) (parmj); \
	do { \
		register TYPE	t = *pi;	\
		*pi++ = *pj;			\
		*pj++ = t;			\
        } while (--i > 0);	\
}

#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
	es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;

void
swapfunc(char *a, char *b, int n, int swaptype) {
	if(swaptype <= 1) 
		swapcode(long, a, b, n)
	else
		swapcode(char, a, b, n)
}

#define swap(a, b) \
	if (swaptype == 0) { \
		long t = *(long *)(a); \
		*(long *)(a) = *(long *)(b); \
		*(long *)(b) = t; \
	} else \
		swapfunc(a, b, es, swaptype)

#define vecswap(a, b, n) 	if ((n) > 0) swapfunc(a, b, n, swaptype)

char *
med3(char *a, char *b, char *c, int (*cmp)(char * , char *)) {
	return cmp(a, b) < 0 ?
	       (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
              :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
}

#define min(a, b) (a) < (b) ? a : b

void
nqsort(char *a, unsigned int n, int es, int (*cmp)(char *, char *)) {
	char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
	int d, r, swaptype;

	SWAPINIT(a, es);
	if (n < 7) {
		for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
			for (pl = pm; pl > (char *)a && cmp(pl - es, pl) > 0; pl -= es)
				swap(pl, pl - es);
		return;
	}
	pm = (char *)a + (n / 2) * es;
	if (n > 7) {
		pl = (char *)a;
		pn = (char *)a + (n - 1) * es;
		if (n > 40) {
			d = (n / 8) * es;
			pl = med3(pl, pl + d, pl + 2 * d, cmp);
			pm = med3(pm - d, pm, pm + d, cmp);
			pn = med3(pn - 2 * d, pn - d, pn, cmp);
		}
		pm = med3(pl, pm, pn, cmp);
	}
	swap(a, pm);
	pa = pb = (char *)a + es;

	pc = pd = (char *)a + (n - 1) * es;
	for (;;) {
		while (pb <= pc && (r = cmp(pb, a)) <= 0) {
			if (r == 0) {
				swap(pa, pb);
				pa += es;
			}
			pb += es;
		}
		while (pb <= pc && (r = cmp(pc, a)) >= 0) {
			if (r == 0) {
				swap(pc, pd);
				pd -= es;
			}
			pc -= es;
		}
		if (pb > pc)
			break;
		swap(pb, pc);
		pb += es;
		pc -= es;
	}
	pn = a + n * es;
	r = min(pa - (char *)a, pb - pa);
	vecswap(a, pb - r, r);
	r = min(pd - pc, pn - pd - es);
	vecswap(pb, pn - r, r);
	if ((r = pb - pa) > es)
		nqsort(a, r / es, es, cmp);
	if ((r = pd - pc) > es)
		nqsort(pn - r, r / es, es, cmp);
}