#Power.asm
#A program to take an int value number to a power using
#recursion.

#int power(int pow, int value)
#{
#  if(pow < 0)
#    System.exit(0);
#  else if(pow == 0)
#    return 1;
#  else
#    return value * pow(value, pow - 1);
#}

.text
main:
  sub $sp, $sp, 24 #make space for arguments and $ra
  
  #set $a0 here (the power)
  li $a0, 3
  #set $a1 here (the value)
  li $a1, 4
  
  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, $a1  #copy contents of $a1 (the value) into $v0

  bgt $a0, 1, powElse
  beq $a0, 1, powEnd
  beq $a0, $zero, powIfZero

powIfZero:
  li $v0, 1
  add $sp, $sp, 24  #revert stack pointer
  jr $ra


  
powElse:
  sw $a0, 24($sp)  #store value in caller's space
  sub $a0, $a0, 1  #set up new arguments
  jal pow  
  lw $a0, 24($sp)
  mul $v0, $v0, $a1

powEnd:
  lw $ra, 20($sp)  #restore the ra register
  add $sp, $sp, 24
  jr $ra