MODULE fact3;
(*---------------------------------------------------------
File name: fact3.pm
Author: AG, MM
Date: 5/19/05 

Problem: This program computes factorial for the first N items 
on the defined chain.

Example of Execution:
	Enter N?: 10
	N! =  1  2  6 24 120 720 5040 40320 362880 3628800

Cycles:
N shifts + N multiplications.
*)
(*----------------------------------------------------------
		CONFIGURATION
----------------------------------------------------------*)
CONST  MAXCELLS=1024; (* MAXCELLS cells in one line *)

CONFIGURATION chain[0..(MAXCELLS - 1)];
CONNECTION
		left: chain [i] -> chain[(i-1) MOD MAXCELLS];
		right: chain[i] -> chain[(i+1) MOD MAXCELLS];
(*----------------------------------------------------------
		VARIABLES
----------------------------------------------------------*)
VAR 
		LFact, LN: chain OF INTEGER;
		K, RightLimit: INTEGER;
(*----------------------------------------------------------
		MAIN
----------------------------------------------------------*)
BEGIN
	(*reading*)
	WriteString("Enter N?: "); ReadInt(RightLimit); (* Read N *)
	
	(*initializing data *)
	LN:= ID(chain); (* LN = 1 2 3 4 5 6.. *)
	LFact:= LN;     
	
	IF LN <= RightLimit THEN
		FOR K:=1 TO RightLimit DO
			LN:= MOVE.right(LN);	(* Shift LN and multiply it by LFact *)
			LFact:=LFact*LN;
		END; (*WHILE*)
		
		(*printing*)
		WriteString("  N! = " );
		WriteInt(LFact, 2);	(*Only prints the activated cells *)
	END; (*IF *)
END fact3.