Merkkijono

; the whole text section fits in one 64-byte cache line :D

section .text
global _start
_start:

xor eax, eax
lea rsi, [rel buff]
push 10
pop rdx

exit:
xor edi, edi
syscall

cld
xchg eax, edi
xor ecx, ecx

atoi:
xchg eax, ecx
imul dl
add cl, al
push rsi ; gotta keep that 16 byte align
lodsb
push rsi
sub al, '0'
jnc atoi

pop rdi
pop rsi
mov [rsi], dl ; handle space or null after input number
mov al, 'a'

L1:
    cmp [rsi], dl
    stosb
    movsb
    jne L1
inc eax
loop L1

mov edx, edi
sub edx, esi ; mod 2^32 difference < 2^16
mov al, 1
mov edi, eax
syscall

push 60
pop rax
jmp exit

section .bss
buff:   resb 0x21000

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED