From 2fb43126152646435f72bc1242d36533bf3231ae Mon Sep 17 00:00:00 2001
From: Kwarde <kevin@kwarde.com>
Date: Sun, 6 Jul 2025 11:15:58 +0200
Subject: [PATCH] Adds strcpy()

---
 src/string.asm | 33 +++++++++++++++++++++++++++
 src/tests.asm  | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/src/string.asm b/src/string.asm
index 9205533..011f110 100644
--- a/src/string.asm
+++ b/src/string.asm
@@ -2,6 +2,7 @@
 
 section .text
 	global	strlen
+	global	strcpy
 
 ;----- strlen(*str[]) -----;
 ; Gets the length of given string
@@ -19,3 +20,35 @@ strlen:
 	not	rax
 	dec	rax
 	ret
+
+;----- strcpy(*dest[], *src[], maxLength) -----;
+; Copies one string (src) into the other (dest), overwriting dest
+; NOTE: maxLength must never exceed size of dest[]. 
+; Return value: Pointer to dest
+; Used registers:
+;	rax*	(ret) Pointer to dest[]
+;	rdi	(arg) Pointer to dest[]
+;	rsi	(arg) Pointer to src[]
+;	rdx	(arg) Max amount of characters to copy / size of dest[] <!>Must never be greater than size of dest[]!
+;	rcx*	Counter for movsb
+;	r8*	Backup for rdi
+strcpy:
+	mov	r8, rdi
+	mov	rdi, rsi
+	call	strlen
+	mov	rcx, rdx
+	cmp	rcx, rax
+	je	.decMaxLen ;rcx-1 for EOS
+	ja	.setMaxLen ;set rcx to strlen(src)
+	jmp	.copy
+	.decMaxLen:
+	dec	rcx
+	jmp	.copy
+	.setMaxLen:
+	mov	rcx, rax
+	.copy:
+	mov	rdi, r8
+	rep	movsb
+	mov	byte [rdi], EOS
+	mov	rax, r8
+	ret
diff --git a/src/tests.asm b/src/tests.asm
index 0ce111b..bece942 100644
--- a/src/tests.asm
+++ b/src/tests.asm
@@ -7,12 +7,20 @@ extern	print
 extern	puts
 ; string.asm
 extern	strlen
+extern	strcpy
 ; convert.asm
 
 section .rodata
 	TEST_print		equ	1
 	TEST_puts		equ	1
 	TEST_strlen		equ	1
+	TEST_strcpy		equ	1
+
+	str1			db	"Hello, world!",EOS
+	str2			db	"Hello, World!",EOS
+	str3			db	"Hello world!",EOS
+	str4			db	"Howdy environment!",EOS
+	str5			db	"The quick brown fox jumps over the lazy dog",EOS
 
 	; print()
 	msgPrint		db	"TEST print()",NL,EOS
@@ -24,9 +32,18 @@ section .rodata
 	strlenStr1		db	"Hello",EOS
 	strlenStr2		db	"Hello, world!",NL,EOS
 
+	; strcpy()
+	msgStrcpy		db	"TEST strcpy()",NL,EOS
+	strcpy1			db	TAB,"strcpy(strBuff1, str1, 12): ",NL,TAB,TAB,EOS
+	strcpy2			db	TAB,"strcpy(strBuff1, str1, 13): ",NL,TAB,TAB,EOS
+	strcpy3			db	TAB,"strcpy(strBuff1, str1, 32): ",NL,TAB,TAB,EOS
+	strcpy4			db	TAB,"strcpy(strBuff1, str5, 32): ",NL,TAB,TAB,EOS
+
 section .data
 
 section .bss
+	strBuff1		resb	32
+	strBuff2		resb	4
 
 section .text
 	global _start
@@ -63,6 +80,51 @@ _start:
 	call	strlen
 %endif
 
+;---
+;--- strcpy()
+;---
+%if TEST_strcpy
+	lea	rdi, [rel msgStrcpy]
+	call	print
+
+	; TEST 1
+	lea	rdi, [rel strcpy1]
+	call	print
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str1]
+	mov	rdx, 12
+	call	strcpy
+	mov	rdi, rax
+	call	puts
+	; TEST 2
+	lea	rdi, [rel strcpy2]
+	call	print
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str1]
+	mov	rdx, 13
+	call	strcpy
+	mov	rdi, rax
+	call	puts
+	; TEST 3
+	lea	rdi, [rel strcpy3]
+	call	print
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str1]
+	mov	rdx, 32
+	call	strcpy
+	mov	rdi, rax
+	call	puts
+	; TEST 4
+	lea	rdi, [rel strcpy4]
+	call	print
+	lea	rdi, [rel strBuff1]
+	lea	rsi, [rel str5]
+	mov	rdx, 32
+	call	strcpy
+	mov	rdi, rax
+	call	puts
+%endif
+
 ;---
 ;--- exit()
 ;---