ak3-labs-asm/lab1_v2.S

.syntax unified
.cpu cortex-m4
.thumb

.macro BKPT_WRITE addr_src
    mov r1, \addr_src
    mov r0, 0x4
    bkpt 0xAB
.endm

#define A 0x0321
#define B 0x7005
#define C 0x0050

.section .text

lab1_v2:
    push.n {lr}

    bl calculate_formula_v2
    bl int_to_str

    pop.n {pc}

calculate_formula_v2:
    ldr r0, =A
    ldr r1, =B
    ldr r2, =C

    cmp r0, r1
    bgt gret
    blt less

    same: @ default
    add r2, r0, r2, lsr #3
    add r0, r2, r1
    b finish

    gret:
    rsb r0, r0, #192
    sub r0, r0, r1
    add r0, r2, r0, lsl #2
    b finish

    less:
    orr r1, r1, r2
    mul r0, r0, r1

    finish:
    mov r10, r0
    mov pc, lr

int_to_str:
    mov r3, sp

    @ write newline + NULL terminator
    mov r5, #0x000A
    strh r5, [r3, #-2]!

    @ --- handmade modulo ---
    mov r4, #10

    iterate:
    mov  r1, r0       @ save orig to r1
    udiv r0, r0, r4   @ orig/10 and overwrite old orig value
    mul  r2, r0, r4   @ orig/10*10, place separately
    subs r5, r1, r2   @ orig - orig/10*10 => modulo (and update flags)

    beq check_if_pending_digits_exist
    proceed_with_conversion:

    add r5, #48           @ int -> char (only digits, so it's fine)
    strb r5, [r3, #-1]!   @ write next char to RAM
    b iterate

    check_if_pending_digits_exist:
    cmp r0, #0
    bne proceed_with_conversion

    BKPT_WRITE r3

    mov pc, lr