Question

Write a MIPS assembly language procedure that simulates/implements the multiplication of two unsigned integers. The procedure receives the mulitiplicand and the multiplier and returns the product. IT CANNOT USE A MULTIPLY INSTRUCTION! Write a MIPS assembly language program that demonstrates your multiplication procedure. Your program should ask the user for two integers to multiply. You can assume that the input integers are positive. Adhere to the procedure call convention.

Answer 1

Lines of procedure without using Mult function:

.data

promptStart: .asciiz "This prrogram does AxB without using mult"
getA: .asciiz "Please enter the first number(multiplicand): "
getB: .asciiz "Please enter the second number(multiplier): "

space: .asciiz " "

result: .asciiz "The product, using my program is: "
endLine: .asciiz "\n"
.text
main:
#"welcome" screen
li $v0,4 # code for print_string
la $a0,promptStart # point $a0 to prompt string
syscall # print the prompt

li $v0,4 # code for print_string
la $a0,endLine # point $a0 to prompt string
syscall # print the prompt

#prompt for multiplicand
li $v0,4 # code for print_string
la $a0,getA # point $a0 to prompt string
syscall # print the prompt

#acquire multiplicand
li $v0,5 # code for read_int
syscall # get an int from user --> returned in $v0
move $s0,$v0 # move the resulting int to $s0

move $s4,$s0 #copy of multiplicand to use in multu

#prompt for multiplier
li $v0,4 # code for print_string
la $a0,getB # point $a0 to prompt string
syscall # print the prompt

#acquire multiplier
li $v0,5 # code for read_int
syscall # get an int from user --> returned in $v0
move $s1,$v0 # move the resulting int to $s0

move $s5,$s1 #copy of multiplier to use in multu

jal MyMult
j print

MyMult:
#$s2 -> lw product, $s1 -> hw multiplier, $s0 -> multiplicand
beq $s1, $0, done # if multiplier=0--> mult gives 0
beq $s0, $0, done
move $t0, $0 #initialize 'counter'= 31
add $t0, $t0, 31
move $s2, $0 #initialize product = 0

loopOut:
beq $t0, $0, done #loop check

andi $t1, $s1, 1 #Stores LSB(MSB?) of $s1 in $t1
bne $t1, $0, loopIn #check if LSB is equal to 1
srl $s1, $s1, 1
srl $s2, $s2, 1 #right shift product & multiplier
add $t0, $t0,-1 # counter = counter -1
j loopOut

loopIn:
addu $s2, $s2, $s0 #Lw product($s2/$s1)+= multiplicand($s0)
sltu $t2, $s2, $s0 #catch carry-out(0 or 1) and stores in $t2

srl $s1, $s1, 1
srl $s2, $s2, 1 #right shift pro-plier..how to save LSB of $s2?

#add carry-out $t2 to LSB of product $s2
addu $s2, $s2, $t0 #Is this right?

addu $t0, $t0,-1 # counter = counter -1
j loopOut

done:
jr $ra

print:
# print result string
li $v0,4 # code for print_string
la $a0,result # point $a0 to string
syscall # print the result string

# print out the result
li $v0,1 # code for print_int
move $a0,$s2 # put result in $a0
syscall # print out result

li $v0,4 # code for print_string
la $a0,space # point $a0 to string
syscall # print the result string

li $v0,1 # code for print_int
move $a0,$s1 # put result in $a0
syscall # print out result

# print the line feed
li $v0,4 # code for print_string
la $a0,endLine # point $a0 to string
syscall # print the linefeed

I hope you got your answer.