program Factorial
/******************************************************************************
 * Description:  Computes the factorial of N. Please note that the highest value 
 *               of N that can be processed without overflow is 0007.  
 *               Negative N will return an answer of 1.
 * Input:        N
 * Output:       N!
 ******************************************************************************/

// Initialize
10: 7101   R[1] <- 0001                  
11: 82FF   read R[2]                     
12: 7301   R[3] <- 0001                  

// Multiply, decrement, and loop
13: 1A30   R[A] <- R[3]                  |
14: 1B20   R[B] <- R[2]                  |
15: FF30   R[F] <- PC; goto 30           | function call
16: 13C0   R[3] <- R[C]                  |
17: 2221   R[2] <- R[2] - R[1]           
18: D213   if (R[2] > 0) goto 13         

// Print n!
19: 93FF   write R[3]                    
1A: 0000   halt                          

function multiply
// Input:                R[A] and R[B] (should be passed by value)
// Return address:       R[F]
// Output:               R[C] = R[A] * R[B]
// Temporary variables:  R[1] = 1

30: 7C00   R[C] <- 0000                  
31: 7101   R[1] <- 0001                  
32: CA36   if (R[A] == 0) goto 36        
33: 1CCB   R[C] <- R[C] + R[B]           
34: 2AA1   R[A] <- R[A] - R[1]           
35: C032   goto 32                       
36: EF00   goto R[F]