;r0        = value to check
;r1        = offset for ldr/str
;r2        = counting for loops/conditions
;r3        = tmp register for shifting
;r4        = result
main:
    mov r0, #0x44
    mov r1, #0x1000
    mov r2, #0
    mov r3, #0
setup:
    cmp r2, #4 ;just write ABCD to 0x1000 for test
    beq clear
    strb r0, [r1, r2]
    sub r0, r0, #1
    add r2, r2, #1
    b        setup
clear:
    eor r0, r0, r0
    eor r1, r1, r1
    eor r1, r1, r1
    eor r2, r2, r2
    b hex
hex:
    mov r1, #0x1000
    ldrb r0, [r1, r2]
    cmp r0, #0x67
    bgt zero
    cmp r0, #0x3A
    addgt r0, r0, #9
    and r0, r0, #0xF
    b shift
zero:
    mov r0, #0
    b shift
shift:
    lsl r0, r0, r3
    orr r4, r4, r0
    add r2, r2, #1
    add r3, r3, #4
    cmp r2, #4
    bne hex