#Copyright 2021 by John Bowman
#Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), 
#to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, 
#and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
#The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
#THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
#FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
#WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

#This program performs multiplication by implementing the Russian peasant's algorithm

#Developed using MARS 4.5 MIPS Assembler and Runtime Simulator

.data
lblFirst: .asciiz "Enter a number: "
lblSecond: .asciiz "Enter another number: "
lblResult: .asciiz "The product of the two numbers is: "

.text
#Ask for first number
li $v0, 4
la $a0, lblFirst
syscall

#Receive first number from console
li $v0, 5
syscall

#Fetch return value and store in $t0
move $t0, $v0

#Ask for second number
li $v0, 4
la $a0, lblSecond
syscall

#Receive second number from console
li $v0, 5
syscall

#Fetch return value and store in $t1
move $t1, $v0

#Initialize variables for branching tests
addi $t2,$zero,2
addi $t5,$zero,1

loop:
  beqz $t0, exit #When $t0 equals zero, terminate loop
    divu $t0,$t2
    mfhi $t3 #Fetch remainder
    beq $t3, $t5, incrementProduct #increment product if remainder is equal to 1
    
    continueLoop:
      sll $t1,$t1,1 #Double $t1 by two
      srl $t0,$t0,1 #Divide $t2 by two
  j loop

incrementProduct:
  add $t4, $t4, $t1
  j continueLoop

exit:
  #Print result description
  li $v0, 4
  la $a0, lblResult
  syscall

  #Print result
  li $v0, 1
  la $a0, ($t4)
  syscall
     
  #Terminate program
  li $v0, 10
  syscall