diff -r cd9fd0986555 config.def.h
--- a/config.def.h	Mon May 19 20:29:57 2008 +0100
+++ b/config.def.h	Wed May 21 13:04:59 2008 +0200
@@ -19,6 +19,7 @@
 Rule rules[] = {
 	/* class      instance    title       tags ref      isfloating */
 	{ "Gimp",     NULL,       NULL,       NULL,         True },
+	{ "Firefox",  NULL,       NULL,       1 << 8,       True },
 };
 
 /* layout(s) */
diff -r cd9fd0986555 dwm.c
--- a/dwm.c	Mon May 19 20:29:57 2008 +0100
+++ b/dwm.c	Wed May 21 13:04:59 2008 +0200
@@ -51,6 +51,7 @@
 #define LENGTH(x)       (sizeof x / sizeof x[0])
 #define MAXTAGLEN       16
 #define MOUSEMASK       (BUTTONMASK|PointerMotionMask)
+#define TAGMASK         ((int)((1LL << LENGTH(tags) + 1) - 1))
 
 /* enums */
 enum { CurNormal, CurResize, CurMove, CurLast };        /* cursor */
@@ -68,7 +69,7 @@
 	long flags;
 	unsigned int bw, oldbw;
 	Bool isbanned, isfixed, isfloating, isurgent;
-	Bool *tags;
+	unsigned int tags;
 	Client *next;
 	Client *prev;
 	Client *snext;
@@ -107,7 +108,7 @@
 	const char *class;
 	const char *instance;
 	const char *title;
-	const char *tag;
+	unsigned int tags;
 	Bool isfloating;
 } Rule;
 
@@ -198,7 +199,7 @@
 int screen, sx, sy, sw, sh;
 int bx, by, bw, bh, blw, wx, wy, ww, wh;
 int mx, my, mw, mh, tx, ty, tw, th;
-int seltags = 0;
+unsigned int seltags = 0;
 int (*xerrorxlib)(Display *, XErrorEvent *);
 unsigned int numlockmask = 0;
 void (*handler[LASTEvent]) (XEvent *) = {
@@ -218,7 +219,7 @@
 Atom wmatom[WMLast], netatom[NetLast];
 Bool otherwm, readin;
 Bool running = True;
-Bool *tagset[2];
+unsigned int tagset[] = {1, 1}; /* after start, first tag is selected */
 Client *clients = NULL;
 Client *sel = NULL;
 Client *stack = NULL;
@@ -231,14 +232,15 @@
 
 /* configuration, allows nested code to access above variables */
 #include "config.h"
-#define TAGSZ (LENGTH(tags) * sizeof(Bool))
+
+/* check if all tags will fit into a unsigned int bitarray. */
+static char tags_is_a_sign_that_your_IQ[sizeof(int) * 8 < LENGTH(tags) ? -1 : 1];
 
 /* function implementations */
 
 void
 applyrules(Client *c) {
 	unsigned int i;
-	Bool matched = False;
 	Rule *r;
 	XClassHint ch = { 0 };
 
@@ -250,18 +252,15 @@
 		&& (!r->class || (ch.res_class && strstr(ch.res_class, r->class)))
 		&& (!r->instance || (ch.res_name && strstr(ch.res_name, r->instance)))) {
 			c->isfloating = r->isfloating;
-			if(r->tag) {
-				c->tags[idxoftag(r->tag)] = True;
-				matched = True;
-			}
+			c->tags |= r->tags & TAGMASK;
 		}
 	}
 	if(ch.res_class)
 		XFree(ch.res_class);
 	if(ch.res_name)
 		XFree(ch.res_name);
-	if(!matched)
-		memcpy(c->tags, tagset[seltags], TAGSZ);
+	if(!c->tags)
+		c->tags = tagset[seltags];
 }
 
 void
@@ -501,13 +500,13 @@
 	for(c = stack; c && !isvisible(c); c = c->snext);
 	for(i = 0; i < LENGTH(tags); i++) {
 		dc.w = textw(tags[i]);
-		if(tagset[seltags][i]) {
+		if(tagset[seltags] & 1 << i) {
 			drawtext(tags[i], dc.sel, isurgent(i));
-			drawsquare(c && c->tags[i], isoccupied(i), isurgent(i), dc.sel);
+			drawsquare(c && c->tags & 1 << i, isoccupied(i), isurgent(i), dc.sel);
 		}
 		else {
 			drawtext(tags[i], dc.norm, isurgent(i));
-			drawsquare(c && c->tags[i], isoccupied(i), isurgent(i), dc.norm);
+			drawsquare(c && c->tags & 1 << i, isoccupied(i), isurgent(i), dc.norm);
 		}
 		dc.x += dc.w;
 	}
@@ -861,7 +860,7 @@
 	Client *c;
 
 	for(c = clients; c; c = c->next)
-		if(c->tags[t])
+		if(c->tags & 1 << t)
 			return True;
 	return False;
 }
@@ -886,19 +885,14 @@
 	Client *c;
 
 	for(c = clients; c; c = c->next)
-		if(c->isurgent && c->tags[t])
+		if(c->isurgent && c->tags & 1 << t)
 			return True;
 	return False;
 }
 
 Bool
 isvisible(Client *c) {
-	unsigned int i;
-
-	for(i = 0; i < LENGTH(tags); i++)
-		if(c->tags[i] && tagset[seltags][i])
-			return True;
-	return False;
+	return c->tags & tagset[seltags];
 }
 
 void
@@ -945,7 +939,6 @@
 	XWindowChanges wc;
 
 	c = emallocz(sizeof(Client));
-	c->tags = emallocz(TAGSZ);
 	c->win = w;
 
 	/* geometry */
@@ -980,7 +973,7 @@
 	if((rettrans = XGetTransientForHint(dpy, w, &trans) == Success))
 		for(t = clients; t && t->win != trans; t = t->next);
 	if(t)
-		memcpy(c->tags, t->tags, TAGSZ);
+		c->tags = t->tags;
 	else
 		applyrules(c);
 	if(!c->isfloating)
@@ -1396,11 +1389,6 @@
 	if(!dc.font.set)
 		XSetFont(dpy, dc.gc, dc.font.xfont->fid);
 
-	/* init tags */
-	tagset[0] = emallocz(TAGSZ);
-	tagset[1] = emallocz(TAGSZ);
-	tagset[0][0] = tagset[1][0] = True;
-
 	/* init bar */
 	for(blw = i = 0; LENGTH(layouts) > 1 && i < LENGTH(layouts); i++) {
 		w = textw(layouts[i].symbol);
@@ -1460,14 +1448,11 @@
 
 void
 tag(const char *arg) {
-	unsigned int i;
-
 	if(!sel)
 		return;
-	for(i = 0; i < LENGTH(tags); i++)
-		sel->tags[i] = (arg == NULL);
-	sel->tags[idxoftag(arg)] = True;
+	sel->tags = arg ? 1 << idxoftag(arg) & TAGMASK : TAGMASK;
 	arrange();
+
 }
 
 unsigned int
@@ -1575,27 +1560,25 @@
 
 void
 toggletag(const char *arg) {
-	unsigned int i, j;
+	int i;
 
 	if(!sel)
 		return;
 	i = idxoftag(arg);
-	sel->tags[i] = !sel->tags[i];
-	for(j = 0; j < LENGTH(tags) && !sel->tags[j]; j++);
-	if(j == LENGTH(tags))
-		sel->tags[i] = True; /* at least one tag must be enabled */
+	if(sel->tags ^ 1 << i)
+		sel->tags ^= 1 << i;
 	arrange();
 }
 
 void
 toggleview(const char *arg) {
-	unsigned int i, j;
+	int i;
 
+	if(!sel)
+		return;
 	i = idxoftag(arg);
-	tagset[seltags][i] = !tagset[seltags][i];
-	for(j = 0; j < LENGTH(tags) && !tagset[seltags][j]; j++);
-	if(j == LENGTH(tags))
-		tagset[seltags][i] = True; /* at least one tag must be viewed */
+	if(sel->tags ^ 1 << i)
+		sel->tags ^= 1 << i;
 	arrange();
 }
 
@@ -1622,7 +1605,6 @@
 		focus(NULL);
 	XUngrabButton(dpy, AnyButton, AnyModifier, c->win);
 	setclientstate(c, WithdrawnState);
-	free(c->tags);
 	free(c);
 	XSync(dpy, False);
 	XSetErrorHandler(xerror);
@@ -1771,8 +1753,7 @@
 void
 view(const char *arg) {
 	seltags ^= 1; /* toggle sel tagset */
-	memset(tagset[seltags], (NULL == arg), TAGSZ);
-	tagset[seltags][idxoftag(arg)] = True;
+	tagset[seltags] = arg ? 1 << idxoftag(arg) & TAGMASK : TAGMASK;
 	arrange();
 }