lab2: add int_to_str implementation

lab1_v2.S

@@ -2,26 +2,50 @@
 .cpu cortex-m4
 .thumb
 
-.section .data
-    test_string: .asciz "Hello"
+.macro BKPT_WRITE addr_src
+    mov r1, \addr_src
+    mov r0, 0x4
+    bkpt 0xAB
+.endm
 
 .section .text
 
 lab1_v2:
-    sub sp, #6
-    ldr r0, =test_string
-    mov r1, #5
+    push.n {lr}
 
-    copy_loop:
-    ldrb r2, [r0, r1]
-    strb r2, [sp, r1]
-    subs r1, #1
-    bpl copy_loop
+    mov r0, #2073
+    bl int_to_str
 
-    mov r1, sp
-    mov r0, 0x04
-    bkpt 0xAB
+    pop.n {pc}
 
-    add sp, #6
+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
+
+    finish:
+    BKPT_WRITE r3
 
     mov pc, lr