.text
    .global sort_by_age

sort_by_age:
    push {r4, r5, r6, r7, r8, r9, lr}

    mov r4, r0 // N
    mov r5, r1 // *persons

    mov r6, #0 // i
    mov r7, #1 // j

    b loop

loop:
    cmp r6, r4
    beq finish

    add r7, r6, #1 // j = i + 1
    mov r8, r6 // index_min = i
    b sorting

finish:
    pop {r4, r5, r6, r7, r8, r9, lr}
    bx lr

sorting:
    cmp r7, r4
    beq swap

    mov r0, #48
    mul r0, r0, r7
    add r0, #4
    ldrb r2, [r5, r0] // persons[j].age

    mov r1, #48
    mul r1, r1, r8
    add r1, #4
    ldrb r3, [r5, r1] // persons[index_min].age

    cmp r2, r3
    movlt r8, r7

    add r7, #1

    b sorting

loop_end:
    add r6, #1

    b loop

swap:
    cmp r8, r6
    beq loop_end

    mov r9, #0 //helper
    b loop_swap

loop_swap:
    cmp r9, #48
    beq loop_end

    mov r0, #48
    mul r0, r0, r6
    add r0, r9

    mov r1, #48
    mul r1, r1, r8
    add r1, r9

    ldrb r2, [r5, r0]
    ldrb r3, [r5, r1]
    strb r2, [r5, r1]
    strb r3, [r5, r0]

    add r9, #4
    b loop_swap