int_to_string.asm

.data
.balign 4
strbuf: .skip 25
.set strbuf_sz, . - strbuf

.balign 4
newline: .ascii "\n"
.set newline_sz, . - newline

.text
.global _start

; TODO: possibly a div10 macro??

.macro mod aa, bb
mod_\@:
    cmp \aa, \bb
    subge \aa, \bb
    bge mod_\@
.endm

; in:
;   r0 = in_ptr
;   r1 = len
; out: n/a
string_reverse:
    add r1, r0
    sub r1, #1
string_reverse_loop:
    cmp r1, r0
    bxlt lr
    ldrb r2, [r0]
    ldrb r3, [r1]
    strb r3, [r0], #1
    strb r2, [r1], #-1
    b string_reverse_loop

; in:
;   r0 = int
;   r1 = buf
; out: n/a
int_to_string:
    mov r2, r1
    mov r3, #0
    ldr r4, =429496730
    cmp r0, #0
    bge int_to_string_convert
    mov r3, #45 ; add minus symbol if < 0
    neg r0, r0
int_to_string_convert:
    mov r5, #48 ; '0'
    mov r6, r0
    mod r6, #10
    add r5, r6
    strb r5, [r1], #1
    umull r5, r6, r0, r4
    mov r0, r6
    cmp r0, #0
    bgt int_to_string_convert
    cmp r3, #0
    beq int_to_string_done
    strb r3, [r1], #1
int_to_string_done:
    push {lr}
    mov r0, r2
    sub r1, r2
    bl string_reverse
    pop {lr}
    bx lr

_start:
    mov r0, #100
    mov r1, #100
    mul r0, r1
    ldr r1, =strbuf
    ldr r2, =strbuf_sz
    bl int_to_string

    mov r0, #1
    ldr r1, =strbuf
    ldr r2, =strbuf_sz
    mov r7, #4
    swi #0

    mov r0, #1
    ldr r1, =newline
    ldr r2, =newline_sz
    mov r7, #4
    swi #0

    mov r0, #0
    mov r7, #1
    swi #0