MIPS Assembly

factorial.asm

.data ## Data declaration section
	## String to be printed:
	prompt: .asciiz "Enter a non-negative number:\n"
	result: .asciiz "\nThe factorial is: "

.text
main:  
	li $v0, 4
	la $a0, prompt
	syscall

	li $v0,5    #Read the number(n)
	syscall

	move $a1, $v0    # n to $t2
	jal fact #perform the calculation
	
	li $v0, 4
	la $a0, result
	syscall
	
	li  $v0, 1          # service 1 is print integer
    	move $a0, $v1  	    # load desired value into argument register $a0, using pseudo-op
    	syscall
    	
    	li $v0, 10      # end program
    	syscall
	
fact: 
	bgt $a1, 1, fatcr #factorial case
	
	#base case
	move $v1, $a1 # $v1 is the temp val holding the previous calculation
	jr $ra
			
fatcr: 
	sub $sp, $sp, 8 #allocate space in the stack to save return addresses and function parameters
	sw $ra, , 0($sp) #save return address
	sw $a1, 4($sp) #save n
			
	add $a1, $a1, -1 # decrement n to pass to the next function call
	
	jal fact #perform the recursion call
	
	lw $a1, 4($sp) #restore n
	mul $v1, $a1, $v1 # n * fact(n-1)
				
	lw $ra, 0($sp) #restore return address
	add $sp, $sp, 8 #clean up the stack
					
	jr $ra