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global atoi, write_ulong
%include "unistd.asm"
section .text
atoi:
mov ecx, 10
xor eax, eax
.loop:
movzx r8d, byte [rdi]
xor r8d, '0'
cmp r8d, ecx ; minor optimization, comparing with a register generates smaller machine code then comparing with an immediate
jnl .return
xor edx, edx
mul rcx
add eax, r8d
inc rdi ; Move ptr to next character
jmp .loop
.return:
ret
write_ulong:
push rdi ; Push fd onto stack
mov rax, rsi
lea rcx, [rsp - 1]
mov byte [rcx], 0
mov rsi, rcx
mov edi, 10 ; Divisor
.loop:
xor edx, edx
div rdi
xor edx, '0'
dec rsi
mov byte [rsi], dl
test rax, rax
jnz .loop
mov rax, SYS_write
pop rdi ; Pop fd from stack
mov rdx, rcx
sub rdx, rsi
syscall
ret
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