Multiply Two 64 bit Numbers Using 32 Bit Words

I am trying to multiply two 64 bit unsigned numbers using only 32 bit words. I understand how to multiply two 32 bit unsigned numbers but I cant figure out how to get the 64 bit number into two 32 bit words. Can someone give me an idea. Here is my 32 bit multiplication program. Any help would greatly be appreciated as I am new to the spim assembly language.

## $t1 ­ mask
## $t2 ­ multiplier (and right_hand_sum).
## $t3 ­ left_hand_sum.
## $t4 ­ multiplicand.
## $t5 - clear.
## $t6 - rightmost bit of left_hand_sum.
## $t7 - rightmost bit of right_hand_sum.
## $t8 - counter

## $v0 ­ syscall parameter / return values.
## $a0 ­ syscall parameters.
## $a1 ­ syscall parameters.

.text
.globl __start
__start:

## read the two integers
      li $v0, 5             # load multiplicand.
      syscall
      move $t4, $v0

      li $v0, 5             # load multiplier.
      syscall
      move $t2, $v0

      lw $t1, mask
      lw $t5, clear      
      
      li $t8, 32
continue:      
      
      beqz $t8, end


      and $t7, $t1, $t2
      beqz $t7, shift
      add $t3, $t3, $t4

shift:      and $t6, $t3, $t1      # store rightmost bit og l_sum in $t6
      and $t2, $t2, $t5      # clear rightmost bit of r_sum
      or $t2, $t2, $t6      # move stored right bit of l_sum to rightmost position of r_sum
      ror $t2, $t2, 1            # rotate r_sum
      srl $t3, $t3, 1            # shift l_sum right
                        # Use sra for twos complement numbers
      addiu $t8, $t8, -1
      b continue

      
end:      sw $t2, r_sum
      sw $t3, l_sum

      li $v0, 10
      syscall
.data
      r_sum: .word 0
      l_sum: .word 0

      mask:  .word 0x00000001
      clear: .word 0xFFFFFFFE