# comments start with # in column 1
# commands which start with a . (dot) are assembler directives
# which do not generate machine code
.intel_syntax noprefix
.global _main

# put external (system) calls here
.extern _exit 
.extern _getchar
.extern _putchar

.data
# declare variables here		
welcome1: .string "[= Press the letter corrisponding to the option...         =]"
splitter: .string "[-----------------------------------------------------------]"
optiona: .string "[- Option a - enter a string into buffer.                  -]"
optionb: .string "[- Option b - display string to the screen.                -]"
optionc: .string "[- Option c - encode/decode string using rot13 algorithm.  -]" 
optiond: .string "[- Option d - program exits.                               -]"
author: .string  "[=     Author: Anthony Paimany |:| 06037852 |:| 1/2/07     -]"
not1: .string "[- Enter String to be loaded into buffer -]"
not2: .string "[- String loaded into buffer -]"
not3: .string "[- Printing out buffer -]"
choice: .rept 1
		.byte 0
		.endr
buffer: .rept 80 # reserve 80 bytes in memory 
         .byte 0
         .endr

.text
_main:

	lea ebx, splitter
	call wrstring
	call newline
	
	lea ebx, welcome1 
	call wrstring
	call newline
	
	lea ebx, splitter
	call wrstring
	call newline
	
	lea ebx, optiona
	call wrstring
	call newline
	
	lea ebx, optionb
	call wrstring
	call newline

	lea ebx, optionc
	call wrstring
	call newline
	
	lea ebx, optiond
	call wrstring
	call newline
	
	lea ebx, splitter
	call wrstring
	call newline
	
	lea ebx, author
	call wrstring
	call newline
	
	lea ebx, splitter
	call wrstring
	call newline
	
	jmp getoption
	
	
	
	
# programs always end with ...	
exit:
        mov eax, 0
        call _exit


# user-defined subroutines(methods) go here ...

getoption:
	lea ebx, choice
	call getstring
	mov al, choice
	cmp al, 0x61
	je option1
	cmp al, 0x62
	je option2
	cmp al, 0x63
	je option3
	cmp al, 0x64
	je option4
	jmp exit

option1:
	lea ebx, not1
	call wrstring
	call newline
	lea ebx, buffer
	call getstring
	lea ebx, not2
	call wrstring
	call newline
	lea ebx, buffer
	call wrstring
	call newline
	jmp getoption

option2:
	lea ebx, not3
	call wrstring
	call newline
	lea ebx, buffer
	call wrstring
	call newline
	jmp getoption

option3:

option4:
	jmp exit
#subroutine for writting strings
wrstring: 		# ebx contains string pointed to

        mov al, [ebx]       # get character
wh1:    
        cmp al, 0 
        je whe1             # jump if al == 0
whd1:
        push ebx
        push eax
        call _putchar       # display on screen
        add esp, 4
        pop ebx
        inc ebx             # ebx points to next char
        mov al, [ebx]       # get character
        jmp wh1 
whe1:
	ret

newline:
	mov al, 10
	push eax
	call _putchar
	add esp,4
	ret

getstring:	
	push ebx
    call _getchar  # input char
                   # char returned in al
    pop ebx
	
wh2:    
    cmp al, 0x0a   # while not LF do
    je end1        # 
whd2:    
    movb [ebx], al # note movb (see note)
    inc ebx
    push ebx       # point to next location
    call _getchar  # input char
                   # char returned in al
    pop ebx
    jmp wh2 
end1:   
        movb [ebx], 0  # make string null terminated, movb again
		ret



rot13:
       # ls byte of edx contains value to be en/decoded
       # if char >= 0x41 && char <= 0x5a then uppercase
       # if (char+13) > 0x5a then subtract 26
       # if char >= 0x61 && char <= 0x7a then lowercase
       # if (char+13) > 0x7a then subtract 26
       #
       cmpb dl, 0x41
       jl r13l2
       cmpb dl, 0x5a
       ja r13l2
       # uppercase
       addb dl, 13
       cmpb dl, 0x5a
       jle r13l1
       subb dl, 26
r13l1: jmp r13le
r13l2: cmpb dl, 0x61
       jl r13le
       cmpb dl, 0x7a
       ja r13le
       # lowercase
       addb dl, 13
       cmpb dl, 0x7a
       jbe r13le       # b not l, ignore sign bit!
       subb dl, 26
r13le: ret

# end of program