TITLE Assignment7              (Assignment7.asm)

; This program takes a string and deturmines weather or not it is a palendrome.
; 

INCLUDE Irvine16.inc

.data
Prompt BYTE "Please enter a possible Palendrome: ",0	;prompt message
IsPalendrome BYTE "Yes that is a palendrome!",0		;messaage if a palendrome is found
NotPalendrome BYTE "No that is not a palendrome.",0	;message if it is not a palendrome
UserInput BYTE 79 dup(0) ;create a buffer for user input with one digit more than max size so that it always ends with 0 null

.code
main PROC
	mov ax,@data
	mov ds,ax

PROMPTUSER:
	mov dx, OFFSET Prompt	;Move the offset of the prompt message into dx
	call WriteString	;print the message

;Read user input
	mov cx, 78		;move the maximum allowed characters into cx
	mov dx, OFFSET UserInput	;move the offset of the userinput buffer to dx
	call ReadString			;read the user input
;check user input
	mov si, OFFSET UserInput	;put the offset of UserInput into si
	mov bx, [si]			; move th efirst character of UserInput into bx
	cmp bx, 0	;If the string is empty (starts with 0 null)
	je ENDPROG	;end the program	

;print the string back to the user
	mov dx, OFFSET UserInput	;move the offset of the input string into dx
	call WriteString		;print the string

;Check for trivial case of 1 character string
	mov si, OFFSET UserInput	;Place the offset of the UserInput string into ax
	mov bx, [si + 1]		;get the second byte of the userinput string/array
	cmp bx, 0 ;Check if the string is only 1 digit long (second byte is 0 null)
	je NOTP		;announce hat we do not have a palendrome

;Check if we have a palendrome
	mov dx, OFFSET UserInput ;move the offset of the user input into dx
	call Check		;call the Check subroutine
	cmp ax, 0		;compare ax to 0 (0 is not a palendrome, 1 is)
	je NOTP			;Not a palendrome, announce it.
ISP:
	mov dx, OFFSET IsPalendrome ;Move the offset of the IsPalendrome message to dx
	call WriteString		;Print the message
	jmp PROMPTUSER			;prompt again
NOTP:
	mov dx, OFFSET NotPalendrome	;Move the offset of the NotPalendrome message to dx
	call WriteString		;Print the message
	jmp PROMPTUSER			;Prompt again
ENDPROG:
	exit				;end the program
main ENDP

.data
CloneA BYTE 79 dup(0) ;place to store striped string
CloneB BYTE 79 dup(0) ;place to store reversed string

.code
Check PROC uses dx si bx
;takes the offset of a string in dx
;return 0 if the string is not a palendrome
;returns 1 id the string is a palnedrome
;returns are stored in ax

;Uppercase all characters
	mov cx, LENGTHOF CloneA		;Put the length of cloneA into the counter (cx)
	mov si, dx			;mov the offset of UserInput as passed through dx into si
CaseLoop:
	AND byte ptr [si], 11011111b	;uppercase all lowercase characters, we do not care about non alpha characters
	inc si				;incriment to next element in string
	loop CaseLoop			;loop again

;Strip out unnecessary characters
	mov si, dx			;mov the offset of UserInput as passed through dx into si
	mov di, OFFSET CloneA		;mov the offset of CloneA into di
StripLoop:
	mov ax, [si]	;move the first element of UserInput into ax
	cmp ax, 0	;compare ax to null0
	je EndStrip	;if the element is 0 end the stripping
	cmp ax, 'A'	;compare the element to 'A'
	jb NEXT		;if the element is a character lower than A on the ascii scale jump to next
	cmp ax, 'Z'	;compare the element to 'Z'
	ja NEXT		;if the element is above Z on the ascii scale jump to next
	mov ax, [si]	;place the element into the CloneA string
	mov [di], ax	;"		"
	inc di		;incriment to next element of CloneA
NEXT:
	inc si		;incriment to next element of UserInput
	jmp StripLoop	;Re-Loop
EndStrip:

;copy the string in reverse from CloneA into CloneB
	mov cx, LENGTHOF CloneA ;Set the counter to the length of CloneA
	mov ax, OFFSET CloneA	;Set ax to the offset of CloneA
	add ax, LENGTHOF CloneA ;add the Lengthof cloneA to ax so we start at the end of it
	mov si, ax		;move the value in ax to si
	mov di, OFFSET CloneB	;set x to the beginning of CloneB
ReverseLoop:
	mov ax, si
	cmp ax, 0 ;compare ax to 0
	je NextLoop ;if ax is 0 jump to the next loop
	mov dx, [si] ;mov the element of UserInput into dx
	mov [di], dx ;move dx into the element of bx
	inc di		;incriment to the next element in bx
NextLoop:
	dec si		;decriment to the next element of ax
	loop ReverseLoop	;next loop

;Compare strings

;print the 2 strings so I can confirm a hit or miss for testing purposes
	mov dx, OFFSET CloneA
	call WriteString
	mov dx, OFFSET CloneB
	call WriteString

	mov si, OFFSET CloneA	;Place the offset of CloneA into dx
	mov di, OFFSET CloneB	;place the offset if CloneB into bx
	mov ax, 1		;mov 1 into ax (for return)
CompLoop:
	mov bx, [si]	;move the current element of CloneA into bx
	mov dx, [di]	;move the current element of CloneB into dx
	cmp bx, dx	;compare dx and bx
	jne NEQUAL	;if the characters are nto equal we have no palendrome, return 0
	inc si		;incriment to next character of CloneA
	inc di		;incriment to next character of CloneB
	loop CompLoop	;Reloop
	ret		;return 1 when finished
NEQUAL:
	mov ax, 0	;set ax to 0
	ret		;return
Check ENDP
END