Adds fwrite()

src/file.asm

@@ -1,5 +1,6 @@
 %include "src/constants.asm"
 
+extern	strlen
 extern	umask_get
 
 section .rodata
@@ -51,6 +52,7 @@ section .text
 	global	fopen
 	global	fclose
 	global	fexist
+	global	fwrite
 
 ;----- fopen(*file[], char mode) -----;
 ; Opens a file
@@ -146,7 +148,7 @@ fopen:
 	add	rsp, SIZE_QWORD
 	ret
 
-;----- fclose(file) -----;
+;----- fclose(*filePointer) -----;
 ; Closes an opened file
 ; Return value: 0 if file closed. Negative error number if an error occured
 ; Used registers:
@@ -167,11 +169,12 @@ fclose:
 
 ;----- fexist(*file[]) -----;
 ; Checks if given file exists (attempts to open the file)
-; Return value: 0- File closed succesfully. -errno (negative error number) if an error occured
+; Return value: 1- File exists. 0- File does not exist or is a directory
 ; Used registers:
 ;	rax*	(ret)
 ;	rdi	(arg) Pointer to string holding (path+)file name
 fexist:
+	;sub	rsp, SIZE_QWORD
 	mov	rsi, 'r'
 	call	fopen
 	test	rax, rax
@@ -183,4 +186,35 @@ fexist:
 	.not_exist:
 	xor	rax, rax
 	.quit:
+	;add	rsp, SIZE_QWORD
+	ret
+
+;--- fwrite(*filePointer, *data[]) -----;
+; Writes data to given file
+; Return value: Length of given string(data[]), 0 if nothing was written (eg invalid file or file not writable, or data[] is empty)
+; Used registers:
+;	rax*	(ret)
+;	rdi	(arg) Pointer to file
+;	rsi	(arg) Data to write
+;	r8*	Backs up rdi
+;	r9*	Backs up rsi
+fwrite:
+	sub	rsp, SIZE_QWORD
+	xor	rax, rax
+	cmp	rdi, 3
+	jl	.quit
+	mov	r8, rdi
+	mov	r9, rsi
+
+	mov	rdi, rsi
+	call	strlen
+
+	mov	rdx, rax
+	mov	rax, NR_write
+	mov	rdi, r8
+	mov	rsi, r9
+	syscall
+
+	.quit:
+	add	rsp, SIZE_QWORD
 	ret