GetDeskNumber fix, cleanup, and drop support for negative desks.

The function GetDeskNumber would not properly wrap more than once.
For instance the command `GotoDesk 3 0 0` should return a desk between
the minimum desk 0 and the maximum desk 0, but instead this would move
the desk `2` from the current desk, because the wrapping code would
only ever occur once.

In fixing the issue, this also cleans up the logic in the
GetDeskNumber function by better handling all the if cases
and use the modulus function to do the wrapping.

Last, support for negative desks is dropped, since it is not
part of the EWMH spec.

doc/fvwm3_manpage_source.adoc

@@ -7585,8 +7585,8 @@ interpreted as a relative desk number. Two arguments are understood as
 a relative and an absolute desk number. Three arguments specify a
 relative desk and the minimum and maximum of the allowable range. Four
 arguments specify the relative, absolute, minimum and maximum values.
-(Desktop numbers can be negative). If a literal _prev_ is given as the
-single argument, the last visited desk number is used.
+If a literal _prev_ is given as the single argument, the last visited
+desk number is used.
 +
 If _arg1_ is non zero then the next desktop number is the current
 desktop number plus _arg1_.
@@ -7604,8 +7604,9 @@ different desktop.
 +
 The number of active desktops is determined dynamically. Only desktops
 which contain windows or are currently being displayed are active.
-Desktop numbers must be between 2147483647 and -2147483648 (is that
-enough?).
+Desktop numbers must be between 0 and 2147483647 (is that enough?).
+Negative desktop numbers are not supported by the EWMH specifications
+and are no longer supported in fvwm.
 
 *GotoDeskAndPage* screen | prev | _desk_ _xpage_ _ypage_::
 	Switches the current viewport to another desktop and page, similar to

fvwm/virtual.c

@@ -269,7 +269,7 @@ static void _drag_viewport(const exec_context_t *exc, int scroll_speed)
 
 /*
  *
- * Parse arguments for "Desk" and "MoveToDesk" (formerly "WindowsDesk"):
+ * Parse arguments for "GotoDesk" and "MoveToDesk":
  *
  * (nil)       : desk number = current desk
  * n           : desk number = current desk + n
@@ -287,9 +287,7 @@ static void _drag_viewport(const exec_context_t *exc, int scroll_speed)
  */
 static int GetDeskNumber(struct monitor *mon, char *action, int current_desk)
 {
-	int n;
 	int m;
-	int is_relative;
 	int desk;
 	int val[4];
 	int min, max;
@@ -301,93 +299,63 @@ static int GetDeskNumber(struct monitor *mon, char *action, int current_desk)
 	if (MatchToken(action, "next"))
 	{
 		if (current_desk + 1 >= number_of_desktops(mon))
-			return (0);
+			return 0;
 		else
-			return (current_desk + 1);
-	}
-	n = GetIntegerArguments(action, NULL, &(val[0]), 4);
-	if (n <= 0)
-	{
-		return mon->virtual_scr.CurrentDesk;
+			return current_desk + 1;
 	}
-	if (n == 1)
-	{
-		if (is_tracking_shared)
-			return val[0];
-		return current_desk + val[0];
-	}
-	desk = current_desk;
-	m = 0;
-	if (val[0] == 0)
-	{
-		/* absolute desk number */
-		desk = val[1];
-		is_relative = 0;
+
+	switch (GetIntegerArguments(action, NULL, &(val[0]), 4)) {
+		case 2:
+			if (val[0] == 0) {
+				desk = val[1];
+				goto found_desk;
+			}
+		case 1:
+			desk = val[0];
+			if (!is_tracking_shared)
+				desk += current_desk;
+			goto found_desk;
+		case 3:
+			m = 1;
+			break;
+		case 4:
+			m = 2;
+			break;
+		default:
+			return mon->virtual_scr.CurrentDesk;
 	}
-	else
-	{
-		/* relative desk number */
-		desk += val[0];
-		is_relative = 1;
+
+	/* Handle limits. */
+	if (val[m] < val[m + 1]) {
+		min = val[m];
+		max = val[m + 1];
+	} else {
+		/* min > max is nonsense, so swap 'em. */
+		min = val[m + 1];
+		max = val[m];
 	}
-	if (n == 3)
-	{
-		m = 1;
+	if (min < 0) {
+		desk = min;
+		goto found_desk;
 	}
-	if (n == 4)
-	{
-		m = 2;
+
+	/* Return absolute desk number. */
+	if (val[0] == 0 && m == 2) {
+		desk = val[1];
+		if (desk < min)
+			desk = min;
+		if (desk > max)
+			desk = max;
+		goto found_desk;
 	}
-	if (n > 2)
-	{
-		/* handle limits */
-		if (val[m] <= val[m+1])
-		{
-			min = val[m];
-			max = val[m+1];
-		}
-		else
-		{
-			/* min > max is nonsense, so swap 'em. */
-			min = val[m+1];
-			max = val[m];
-		}
-		if (is_relative)
-		{
-			/* Relative moves wrap around.	*/
-			if (desk < min)
-			{
-				desk += (max - min + 1);
-			}
-			else if (desk > max)
-			{
-				desk -= (max - min + 1);
-			}
-		}
-		else if (desk < min)
-		{
-			/* Relative move outside of range, wrap around. */
-			if (val[0] < 0)
-			{
-				desk = max;
-			}
-			else
-			{
-				desk = min;
-			}
-		}
-		else if (desk > max)
-		{
-			/* Move outside of range, truncate. */
-			if (val[0] > 0)
-			{
-				desk = min;
-			}
-			else
-			{
-				desk = max;
-			}
-		}
+
+	desk = (current_desk + val[0]) % (max - min + 1);
+	desk += desk < 0 ? max + 1 : min;
+
+found_desk:
+	if (desk < 0) {
+		fvwm_debug(__func__, "Negative desks are not supported.");
+		return current_desk;
 	}
 
 	return desk;
@@ -2524,6 +2492,8 @@ void CMD_GotoDesk(F_CMD_ARGS)
 		m = monitor_get_current();
 
 	new_desk = GetDeskNumber(m, action, m->virtual_scr.CurrentDesk);
+	if (m->virtual_scr.CurrentDesk == new_desk)
+		return;
 
 	if (is_tracking_shared) {
 		/* Check to see if this monitor is requesting a desktop which