From b4b6364c2fc4b14a0aaac406891c3880243a9733 Mon Sep 17 00:00:00 2001
From: Charles <sircharlesaze@gmail.com>
Date: Sat, 23 Nov 2019 02:54:37 +0100
Subject: refactored mandatory functions, to respect c calling convention

---
 ft_strcmp.s | 50 +++++++++++++++++++++++++-------------------------
 1 file changed, 25 insertions(+), 25 deletions(-)

(limited to 'ft_strcmp.s')

diff --git a/ft_strcmp.s b/ft_strcmp.s
index da8bc1c..5be82a5 100644
--- a/ft_strcmp.s
+++ b/ft_strcmp.s
@@ -12,33 +12,33 @@
 
 global _ft_strcmp
 
+; int ft_strcmp(const char *s1, const char *s2);
 _ft_strcmp:
-	mov rax, rdi  
-	mov rbx, rsi 
-	xor rcx, rcx
+	push r12
+	push r13
+	push rcx
+	mov r12, rdi  ; s1
+	mov r13, rsi  ; s2
+	mov rcx, -1   ; index
 	FT_STRCMP_LOOP:
-		cmp byte [rax + rcx], 0
-		je FT_STRCMP_LOOP_END
-		cmp byte [rbx + rcx], 0
-		je FT_STRCMP_LOOP_END
-		mov dl, byte [rax + rcx]
-		cmp dl, byte [rbx + rcx]
-		jne FT_STRCMP_LOOP_END
 		inc rcx
-		jmp FT_STRCMP_LOOP
+		cmp byte [r12 + rcx], 0   ; check and of s1
+		je FT_STRCMP_LOOP_END
+		mov dl, byte [r12 + rcx]
+		cmp dl, byte [r13 + rcx]  ; s1[rcx] == s2[rcx]
+		je FT_STRCMP_LOOP
 	FT_STRCMP_LOOP_END:
-		mov dl, byte [rax + rcx]
-		cmp dl, byte [rbx + rcx]
-		jl FT_STRCMP_S1_LOWER
-		mov rdx, rax
-		xor rax, rax
-		mov al, [rdx + rcx]
-		sub al, [rbx + rcx]
-		ret
-		FT_STRCMP_S1_LOWER:
-		mov rdx, rax
-		xor rax, rax
-		mov al, [rbx + rcx]
-		sub al, [rdx + rcx]
-		neg eax  
+
+	xor rax, rax
+	mov al, byte [r12 + rcx]
+	sub al, byte [r13 + rcx]
+	jnc FT_STRCMP_END  ; jump end if no substraction overflow
+
+	neg al   ; negate al to cancel overflow
+	neg eax  ; negate the whole int since the function returns that type
+
+	FT_STRCMP_END:
+	pop rcx
+	pop r13
+	pop r12
 	ret
-- 
cgit