Caesar cipher encrypting a single character in MIPS

Question

I\'m having some problems in creating a program to encrypt a message. At this point i\'m just trying to input a char and the output should be the char+5 positions in the alphabe

Answer 1

If you are using MIPS, the code should be like this:

    .text
main:
    li $v0, 8                 # read_string
    la $a0, textbuf           # adresses of char at $a0
    li $a1, 2                 # length to read at $a1
    syscall

    la $t0, textbuf
    lb $v0, 0($t0)            # char ASCII (I GUESS IT SHOULD)
    move $t0, $v0             # moves char(ASCII) to $t0
    li $s0, 90
    li $s1, 65
    bgt $t0, $s0, le_string   # checks if char(ASCII) > 90
    nop                       # avoid instruction after branch begin executed even if jump is taken
    blt $t0, $s1, le_string   # checks if char(ASCII) < 65
    nop                       # avoid instruction after branch begin executed even if jump is taken

    li $s2, 5
    li $s3, 26
    add $t0, $t0, $s2         # char=char+5
    ble $t0, $s0, nowrap_char # checks if encrypted char <= 90
    nop                       # avoid instruction after branch begin executed even if jump is taken
    sub $t0, $t0, $s3         # wrap the char
nowrap_char:
le_string:
    move $t2, $t0             # moves encrypted char to $t2

    la $t0, textbuf
    li $v0, 4                 # print_string
    sb $t2, 0($t0)            # put the encrypted char
    la $a0, textbuf
    syscall

    li $v0, 10                # exit
    syscall

    .data
textbuf:
    .space 2