hamming.s

.globl main

.data
DNA1:
    .asciiz "GAGCCTACTAACGGGAT"
DNA2:
    .asciiz "CATCGTAATGACGGCCT"

.text
main:
    li $v0, 11              # print char 
    move $s0, $zero         # set s0 = 0, the char counter
    move $s1, $zero         # set s1 = 0, the diff char counter
    la $a1, DNA1            # load DNA1 in a1
    la $a2, DNA2            # load DNA2 in a2
    li $t0, 1               # load any non-zero number in t0
    jal loop_string
    
loop_string:
    add $t0, $a1, $s0       # address of byte to examine next (first char + char counter)
    add $t2, $a2, $s0
    lb $t1, 0($t0)          # load *(first char + char counter) in t1
    lb $t3, 0($t2)
    beq $t1, $zero, exit    # exit if null character is met
    bne $t1, $t3, increment # increment diff char counter if the chars are different
    addi $s0, $s0, 1        # increment char counter by 1
    j loop_string

increment:
    addi $s1, $s1, 1        # inrement diff char counter by 1
    addi $s0, $s0, 1        # increment char counter by 1
    jal loop_string

exit:
    move $a0, $s1           # print the diff curr counter
    li $v0, 1               # print int
    syscall
    li $v0, 10              # exit
    syscall