Assembly - Recursive function that recursively returns the factorial of various numbers

recursive_function.s

#Recursive Function

#PURPOSE - Given a number, this program computes the factorial.
# For example, the factorial of 3 is 3*2*1, or 6.
# The factorial of 4 is 4*3*2*1

# This program shows how to call a function recursively

.section  .data

#This program has no global data

.section .text
.globl  _start
.globl factorial  #this is unneeded  unless we want to share this function among other programs

_start:
pushl $4			#The factorial takes one argument - the number we want a factorial of.
				#So it gets pushed

call  factorial			#run the factorial function'
addl  $4,  5esp			#Scrubs the parameter that was pushed on the stack
#movl  %eax, %ebx		#factorial returns the answer in %eax, but we want it in %ebx to send it as 				#our status

movl  $1,  %eax		#call the kernel's exit function

#The actual function
.type   factorial, @function
factorial:
push1  %ebp			#standard function stuff = we have to restore %ebp to its prior state vefore 				#returning, so we have to push it.
movl   %esp, %ebp		#This is because we don't want to modify the stack pointer so we use 					#%ebp

movl  8(%ebp), %eax		#This moves the first argument to %eax, 4(%ebp) holds the return 					#address, and 8(%ebp) holds the first parameter
cmpl  $1, 5eax			#If the number is 1, that is our base case, and we simply return 
				#1 is already in %eax as the return value
je  end_factorial
decl  %eax			#otherwise, decrease the value
pushl  %eax			#push it for our call to factorial
call  factorial			#call factorial
movl  8(%ebp), %ebx		#multiply that by the result of the last call to factorial in %eax
				#The answer is stored in 5eax, which is good since that's where return 
				#values go
end_factorial:



movl  %ebp, %esp		#standard function return stuff - we have to restore %ebp and %esp
				#to where they were before the function started #return from the function
				#(this pops the return value, too)
ret