From 08389a5bb23c9217f236532268c5b5db3745d0b0 Mon Sep 17 00:00:00 2001
From: Kwarde <kevin@kwarde.com>
Date: Wed, 9 Jul 2025 23:44:40 +0200
Subject: [PATCH] Adds strcmp() (note: much different than strcmp in C)

---
 src/string.asm | 41 +++++++++++++++++++++++
 src/tests.asm  | 91 ++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 129 insertions(+), 3 deletions(-)

diff --git a/src/string.asm b/src/string.asm
index 44305f0..6f27b48 100644
--- a/src/string.asm
+++ b/src/string.asm
@@ -5,6 +5,7 @@ section .text
 	global	strcpy
 	global	strcat
 	global	strclr
+	global	strcmp
 
 ;----- strlen(*str[]) -----;
 ; Gets the length of given string
@@ -102,3 +103,43 @@ strclr:
 	cld
 	rep	stosb
 	ret
+
+;----- strcmp(*str1[], *str2[]) -----;
+; Compares str2 against str1
+; Return values:
+;	0			Two strings are the same, OR str1 or str2 is empty
+;	Length of str1		str2 is longer than str1, but no difference was found in between str1 and str2 -up to the point str1 ended-
+;	Anything else		Position (index+1) where str1 and str2 differ
+; Used registers:
+;	rax*	(ret)
+;	rdi	Pointer to str1
+;	rsi	Pointer to str2
+;	rcx*	Counter for scasb
+;	rdx*	Length of str1
+;	r8* 	Backup for rdi
+strcmp:
+	mov	rax, -1
+	cmp	byte [rdi], EOS
+	je	.equal
+	cmp	byte [rsi], EOS
+	je	.equal
+
+	mov	r8, rdi
+	call	strlen
+	mov	rcx, rax
+	mov	rdx, rax
+	mov	rdi, r8
+	cld
+	repe	cmpsb
+	je	.equal
+	mov	rax, rdx
+	sub	rax, rcx
+	jmp	.quit
+
+	.equal:
+	cmp	byte [rsi], EOS
+	jne	.quit
+	mov	rax, -1
+
+	.quit:
+	ret
diff --git a/src/tests.asm b/src/tests.asm
index 3d84e6f..388f0af 100644
--- a/src/tests.asm
+++ b/src/tests.asm
@@ -13,6 +13,7 @@ extern	strlen
 extern	strcpy
 extern	strcat
 extern	strclr
+extern	strcmp
 ; convert.asm
 extern	dec2str
 extern	udec2str
@@ -30,6 +31,7 @@ section .rodata
 	TEST_strclr		equ	1
 	TEST_islower		equ	1
 	TEST_isupper		equ	1
+	TEST_strcmp		equ	1
 
 	str1			db	"Hello, world!",EOS
 	str2			db	"Hello, World!",EOS
@@ -96,7 +98,7 @@ section .rodata
 	strclr1b		db	TAB,"print(strBuff1[3]): ",NL,TAB,TAB,EOS
 	strclr2			db	TAB,"strcat(strBuff1, str5, 32)",NL,TAB,"strclr(strbuff1, 2)",NL,TAB,"print(strbuff1[3]): ",NL,TAB,TAB,EOS
 
-	;islower()
+	; islower()
 	msgIslower		db	NL,"TEST islower()",NL,EOS
 	islower1		db	TAB,"islower(str1[0]): %d",NL,EOS
 	islower2		db	TAB,"islower(str1[1]): %d",NL,EOS
@@ -104,7 +106,7 @@ section .rodata
 	islower4		db	TAB,"islower('D'): %d",NL,EOS
 	islower5		db	TAB,"islower('!'): %d",NL,EOS
 
-	;isupper()
+	; isupper()
 	msgIsupper		db	NL,"TEST isupper()",NL,EOS
 	isupper1		db	TAB,"isupper(str1[0]): %d",NL,EOS
 	isupper2		db	TAB,"isupper(str1[1]): %d",NL,EOS
@@ -112,6 +114,15 @@ section .rodata
 	isupper4		db	TAB,"isupper('D'): %d",NL,EOS
 	isupper5		db	TAB,"isupper('!'): %d",NL,EOS
 
+	; strcmp()
+	msgStrcmp		db	NL,"TEST strcmp()",NL,EOS
+	strcmp1			db	TAB,"strcmp(str1, str1): %d",NL,EOS
+	strcmp2			db	TAB,"strcmp(str1, str2): %d",NL,EOS
+	strcmp3			db	TAB,"- strcpy(strBuff1, str1)",NL,TAB,"- strcat(strBuff1, str2)",NL,TAB,"> strBuff1: %s",NL,TAB,"> str1: %s",NL,TAB,"strcmp(str1, strBuff1): %d",NL,EOS
+	strcmp4			db	TAB,"strcmp(strBuff1, str1): %d",NL,EOS
+	strcmp5			db	TAB,"- strclr(strBuff1, 32)",NL,TAB,"strcmp(strBuff1, str1): %d",NL,TAB,"strcmp(str1, strBuff1): %d",NL,EOS
+	strcmp6			db	TAB,"strcmp(str1, str5): %d",NL,EOS
+
 section .data
 
 section .bss
@@ -408,9 +419,11 @@ _start:
 	lea	rdi, [rel strBuff1]
 	mov	rsi, 2
 	call	strclr
+	;lea	rdi, [rel strBuff1] ;will add output for this later < works as expected tho
+	;call	puts
 	lea	rdi, [rel strBuff1]
 	add	rdi, 3
-	call puts
+	call	puts
 %endif
 
 ;---
@@ -499,6 +512,78 @@ _start:
 	call	printf
 %endif
 
+;---
+;--- strcmp()
+;---
+%if TEST_strcmp
+	lea	rdi, [rel msgStrcmp]
+	call	printf
+
+	; TEST 1
+	lea	rdi, [rel str1]
+	lea	rsi, [rel str1]
+	call	strcmp
+	lea	rdi, [rel strcmp1]
+	mov	rsi, rax
+	call	printf
+
+	; TEST 2
+	lea	rdi, [rel str1]
+	lea	rsi, [rel str2]
+	call	strcmp
+	lea	rdi, [rel strcmp2]
+	mov	rsi, rax
+	call	printf
+
+	; TEST 3
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str1]
+	call	strcpy
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str2]
+	call	strcat
+	lea	rdi, [rel str1]
+	lea	rsi, [rel strBuff1]
+	call	strcmp
+	lea	rdi, [rel strcmp3]
+	lea	rsi, [rel strBuff1]
+	lea	rdx, [rel str1]
+	mov	rcx, rax
+	call	printf
+
+	; TEST 4
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str1]
+	call	strcmp
+	lea	rdi, [rel strcmp4]
+	mov	rsi, rax
+	call	printf
+
+	; TEST 5
+	lea	rdi, [rel strBuff1]
+	mov	rsi, 32
+	call	strclr
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str1]
+	call	strcmp
+	mov	rbx, rax
+	lea	rdi, [rel str1]
+	lea	rsi, [rel strBuff1]
+	call	strcmp
+	lea	rdi, [rel strcmp5]
+	mov	rsi, rbx
+	mov	rdx, rax
+	call	printf
+
+	; TEST 6
+	lea	rdi, [rel str1]
+	lea	rsi, [rel str5]
+	call	strcmp
+	lea	rdi, [rel strcmp6]
+	mov	rsi, rax
+	call	printf
+%endif
+
 ;---
 ;--- exit()
 ;---