#Power2.asm
#
#An updated version of the power function
#compute power(x,y) where the result is x^y

.text
main:
  sub $sp, $sp, 24 #make space for arguments and $ra
  li $a0, 3 #set $a0 (x) here
  li $a1, 7 #set $a1 (y) here
  jal pow
  add $sp, $sp, 24  #return the stack pointer to its original value

  #print the result
  move $a0, $v0
  li $v0, 1
  syscall

  #end the program
  li $v0, 10
  syscall

pow:
  sub $sp, $sp, 24 # Set aside space for arguments and ra (24 bytes)
  sw $ra, 20($sp) #store the ra register

  move $v0, $a0  #copy contents of $a0 (the value of x) into $v0

  bgt $a1, 1, powElse  # if y > 1, jump to powElse
  beq $a1, 1, powEnd   # if y == 1, jump to powEnd
  beq $a1, $zero, powIfZero  # if y == 0, return 1

  #end the program if we have a negative value
  li $v0, 10
  syscall

powIfZero:
  li $v0, 1  #copy 1 into the return register
  add $sp, $sp, 24  #revert stack pointer
  jr $ra  #return


  
powElse:
  sw $a1, 24($sp)  #store value of y in caller's space
  sub $a1, $a1, 1  #set up new arguments
  jal pow   #call pow again
  lw $a1, 24($sp)  # revert $a1 to its original value (note this isn't really necessary)
  mul $v0, $v0, $a0  #multiply x and the return value, and store the result as our new 
                     #return value

  # continue with the code from powEnd

powEnd:
  lw $ra, 20($sp)  #restore the ra register
  add $sp, $sp, 24 #revert the stack pointer (pop the stack)
  jr $ra  #return