1 files changed, 167 insertions, 0 deletions
diff --git a/setCase.asm b/setCase.asm
new file mode 100644
index 0000000..ae3014a
--- /dev/null
+++ b/setCase.asm
@@ -0,0 +1,167 @@
+; Version	: 1.00
+; Updated	: 20/8/2021
+; Licence	: GPLv3
+; Set the case of ASCII text to upper or lower case.
+
+default rel	; we always want this.
+extern printf
+
+%define argv0 r12
+%define upper r13 ;make r13 the boolean
+%define scratch r14
+%define file r15
+
+section .rodata
+	Usage db `%s OPTION [filename]\n Option	Description\n-u Make characters uppercase.\n-l Make characters lowercase.\n`,0
+	OpenError: db `Could not open: %s\n`,0
+
+section .text
+    global main
+
+usage:
+	push rbx		;align the stack if not already done
+
+	mov rsi, [argv0]	;get argv[0]
+	lea rdi, [rel Usage]	;copy the usage to rdi
+	xor eax,eax		;al == 0 means no FP args in XMM registers
+	call printf wrt ..plt	;call printf with `wrt ..plt` so dynamic linking works
+
+	pop rbx			;pop rbx off the stack
+
+	mov eax, 1		;exit with value 1
+	ret
+
+
+
+
+stdin:
+	xor edi, edi		; file descriptor = stdin = 0
+	lea rsi, [scratch]	; buffer = address to store the bytes read
+	mov edx, 1		; number of bytes to read
+	xor eax, eax		; syscall for read == 0
+	syscall
+
+	test eax, eax		; If syscall returns 0 in rax, the character is EOF
+	je exit			; if char is EOF: exit
+
+	call process_char
+	jmp stdin
+
+
+process_char:
+	test upper,upper
+	jz lower		;jump to lower if upper is false
+
+	;fall through if uppercase
+
+	cmp byte[scratch],'a'	;check if read char is below 'a'
+	jl skip_modification	;if below 'a', it's not a lowercase char
+
+	cmp byte[scratch],'z'	;check if read char is equal to or below z
+	ja skip_modification	;if not equal or above, it's not a lowercase char
+
+	sub byte[scratch], 32	;subtract 32 from ASCII char to capitalise it
+	jmp skip_modification	;skip lowercase
+
+lower:
+	cmp byte[scratch],'A'	;check if read char is below 'A'
+	jl skip_modification	;if below 'A', it's not a uppercase char
+
+	cmp byte[scratch],'Z'	;check if read char is equal to or below 'Z'
+	ja skip_modification	;if not equal or above, it's not a lowercase char
+
+	add byte[scratch], 32	;add 32 to ASCII char to make it lowercase
+
+skip_modification:
+	mov edi, 1		; file descriptor = stdout
+	lea rsi, [scratch]	; buffer = address to write to console
+	mov edx, 1		; number of bytes to write
+	mov eax, 1		; SYSCALL number for writing to STDOUT
+	syscall			; make the syscall
+
+	ret	 		; read the next char
+
+
+
+
+file_error:
+	push rbx		;align the stack if not already done
+
+	mov rsi, scratch	;get argv[2]
+	lea rdi, [rel OpenError];copy the filename to rdi
+	xor eax,eax		;al == 0 means no FP args in XMM registers
+	call printf wrt ..plt	;call printf with `wrt ..plt` so dynamic linking works
+
+	pop rbx			;pop rbx off the stack
+
+	mov eax, 1		;exit with value 1
+	ret
+
+open_file:
+	add rsi, 8		;get pointer-to-pointer to argv[2]
+	mov scratch,[rsi]	;get pointer to argv[2] and copy it to scratch
+
+	mov eax, 2		;syscall sys_open
+	mov rdi, scratch	;place pointer to filename string in rdi
+	xor esi, esi		;O_RDONLY
+	xor edx, edx		;don't need a mode
+	syscall
+
+	test eax, eax
+	js file_error		;if nonzero, sys_open failed
+
+	mov file, rax		;store fp in file
+
+read_file:
+	mov rdi, file		;file descriptor = rax from sys_open above
+	lea rsi, [scratch]	;read into scratch
+	mov edx, 1		;number of bytes to read
+	xor eax, eax		;syscall for read == 0
+	syscall
+
+	test eax, eax		;If syscall returns 0 in rax, the character is EOF
+	je close_file		;if char is EOF, close the file and exit
+
+	call process_char
+	jmp read_file
+
+
+
+
+
+main:
+mov argv0, rsi		;save argv[0] for later
+
+cmp edi, 2
+jl usage		;show usage if not enough args are provided
+
+check_args:
+	add rsi, 8	;get pointer-to-pointer to argv[1]
+
+	mov scratch, [rsi] ;get pointer to argv[1] and copy it to scratch
+	cmp byte[scratch], '-'
+	jne usage	;show usage if there is no argument (missing -)
+
+
+	xor upper, upper ;assume lowercase by default
+
+	cmp byte[scratch+1], 'u'
+	jne false	;fall through if argv[1][1] == 'u' and thus set upper boolean to true
+	mov upper,1
+false:
+
+	cmp edi, 3
+	jl stdin	;go to stdin mode if no filename is provided
+	jg usage	;go to usage if more that 3 args are provided
+
+	jmp open_file	;jump to file opening
+
+
+close_file:
+	mov rdi, file		;fp to close
+	mov eax, 3		;sys_close
+	syscall
+
+exit:
+	xor eax, eax
+	ret