power.s

	#PURPOSE:  Program to illustrate how functions work
	#          This program will compute the value of
	#          2^3 + 5^2
	#

	#Everything in the main program is stored in registers,
	#so the data section doesn't have anything.
	.section .data 

	.section .text

	.globl _start
_start:
	pushl $3                  #push second argument
	pushl $2                  #push first argument
	call  power               #call the function
	addl  $8, %esp            #move the stack pointer back

	pushl %eax                #save the first answer before
	                          #calling the next function

	pushl $2                  #push second argument
	pushl $5                  #push first argument
	call  power               #call the function
	addl  $8, %esp            #move the stack pointer back

	popl  %ebx                #The second answer is already
	                          #in %eax.  We saved the 
	                          #first answer onto the stack,
	                          #so now we can just pop it
	                          #out into %ebx

	addl  %eax, %ebx          #add them together
	                          #the result is in %ebx
	
	movl  $1, %eax            #exit (%ebx is returned)
	int   $0x80

	#PURPOSE:  This function is used to compute
	#          the value of a number raised to
	#          a power.
	#
	#INPUT:    First argument - the base number
	#          Second argument - the power to 
	#                            raise it to
	#
	#OUTPUT:   Will give the result as a return value
	#
	#NOTES:    The power must be 1 or greater
	#
	#VARIABLES: 
	#          %ebx - holds the base number
	#          %ecx - holds the power
	#
	#          -4(%ebp) - holds the current result
	#
	#          %eax is used for temporary storage
	#
	.type power, @function
power:
	pushl %ebp           #save old base pointer
	movl  %esp, %ebp     #make stack pointer the base pointer
	subl  $4, %esp       #get room for our local storage

	movl  8(%ebp), %ebx  #put first argument in %ebx
	movl  12(%ebp), %ecx #put second argument in %ecx

	movl  %ebx, -4(%ebp) #store current result

power_loop_start:
	cmpl  $1, %ecx       #if the power is 1, we are done
	je    end_power
	movl  -4(%ebp), %eax #move the current result into %eax
	imull %ebx, %eax     #multiply the current result by
	                     #the base number
	movl  %eax, -4(%ebp) #store the current result 

	decl  %ecx           #decrease the power
	jmp   power_loop_start #run for the next power

end_power:
	movl -4(%ebp), %eax  #return value goes in %eax
	movl %ebp, %esp      #restore the stack pointer
	popl %ebp            #restore the base pointer
	ret