From baf4910870a6e8999802b9a4a22eabd4142a34e3 Mon Sep 17 00:00:00 2001
From: Bond_009 <bond.009@outlook.com>
Date: Thu, 1 Dec 2022 22:30:22 +0100
Subject: Move all Advent of Codes into one repo

---
 utils/utils.asm | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 utils/utils.asm

(limited to 'utils/utils.asm')

diff --git a/utils/utils.asm b/utils/utils.asm
new file mode 100644
index 0000000..5b65f15
--- /dev/null
+++ b/utils/utils.asm
@@ -0,0 +1,43 @@
+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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