.text
main:
    li  $a0, 0x214D # $a0 = 0, change this to test different values

    jal hexasc      # call hexasc
    nop         # delay slot filler (just in case)

    move    $a0, $v0    # $a0 = $v0, copy return value to argument register

    li  $v0, 11     # syscall with v0 = 11 will print out
    syscall         # ascii character in a0 to the Run I/O window

    li  $v0, 10     # system exit code
    syscall         # terminates execution, no garbage memory will be executed

hexasc:
    # $a0 = $a0 & 0xF
    # if ($a0 >= 0 && $a0 <= 9 && $a0 is int)
    #   $v0 = 0x30 + $a0
    # else if ($a0 >= 10 && $a0 <= 15)
    #   $v0 = 0x37 + $a0
    # else $v0 = 0

    addi    $t0, $0, 15         # $t0 = 15 (upper bound)
    addi    $t1, $0, 9          # $t1 = 9 (bound between numbers and letters)
    andi    $a0, $a0, 0xF           # 28 zeros concatinated with the last 4 bits of $a0

    bltz    $a0, out_of_domain      # branch to out_of_domain, if $a0 < 0
    bgt     $a0, $t0, out_of_domain     # branch to out_of_domain, if $a0 > 15
    bgt     $a0, $t1, gt9           # branch to gt9, if $a0 > 9

    addi    $v0, $a0, 0x30          # convert $a0 to ascii code for 0-9
    jr  $ra

out_of_domain:
    move $v0, $0    # $v0 = 0 (ascii for NUL)
    jr $ra

gt9:
    addi $v0, $a0, 0x37 # convert $a0 to ascii code for A-F
    jr $ra