;=============================================================================================================================================
;																	ordin.asm
;This program is designed to calculate the ascii difference between 2 letters
;																	Algorithm
;D1: Get the letter
;D2: Get the second one
;D3: Calculate and show the difference
;D4: Show signature and exit
;(C)I don't take any responsibility for the use of this program
;															Zedr0n -- connection closed
;=============================================================================================================================================
;=============================================================================================================================================
; Macros
;=============================================================================================================================================
crlf    macro
    mov ah,02h
    mov dl,0Dh
    int 21h
    mov dl,0Ah
    int 21h	
        endm
print   macro    message
    mov ah,09h
    mov dx,offset &message&
    int 21h
        endm
readsym macro	data
    mov ah,01h
    int 21h
	mov byte ptr &data&,al
		endm
;============================================================================================================================================
; .Com declaration
;============================================================================================================================================
.model tiny
.data
signature       db      0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,
                        db      "                     ---------------------------------  ",0Dh,0Ah,
                        db      "                     \  Zedr0n - connection closed   / ",0Dh,0Ah,
                        db      "                      \         02.11.2001          /  ",0Dh,0Ah,
                        db      "                       ----------------------------- ",0Dh,0Ah,
                        db      0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,0Dh,0Ah,
                        db      '$'
welcome1	db	"Enter the first letter: $"
welcome2	db	"Enter the second letter: $"
result		db	"The difference is $"
First	db	?
Second	db	?
.code
.386
org 100h
start:
;============================================================================================================================================
; Code segment
;============================================================================================================================================
D1:
    print welcome1
    readsym First
    crlf
D2:
	print welcome2
	readsym Second
	crlf
D3:
    xor eax,eax
    xor ebx,ebx
    xor edx,edx
    mov al,First
    mov bl,Second
    sub al,bl
    call hexdec
    call output
    xor ah,ah
    int 16h
D4:
    mov ah,9h
    mov dx,offset signature
    int 21h
    ret
;=============================================================================================================================================
; Procedures
;=============================================================================================================================================
;=============================================================================================================================================
; Convert hexadecimal in eax to decimal in edx
;=============================================================================================================================================
hexdec proc
	mov edx,eax
	mov    esi,offset divtab              ;pointer subtract values
	mov     edi,offset numbuff              ;output buffer
	mov     cx,10                   ;5 digits
sublop: xor     al,al                   ;clear counter
sblop:  cmp     edx,[esi]               ;number < subractor ?
        jb      tolow                   ;yeah
        sub     edx,[esi]               ;noo, subtract
        add     al,1                    ;incrase times subtracted
        jmp     sblop                   ;subtract again
tolow:  add     al,30h                  ;make ascii
        stosb                           ;store in buffer
        add     esi,4                    ;next subtractor
        loop    sublop                  ;do it
        mov     al,0                    ;null terminate buffer
        stosb
        mov esi,offset numbuff
        ret
divtab: 	                   ;subractor values
        dd 1000000000
        dd  100000000
        dd   10000000
        dd    1000000
        dd     100000	 
        dd      10000           
        dd       1000
        dd        100
        dd         10
        dd          1
numbuff db  34 dup(0)                ;number buffer
hexdec endp
;=============================================================================================================================================
; Outputs buffer with ascii, where si points to buffer  
;=============================================================================================================================================
output proc
strip:
        lodsb                           ;load byte
        cmp     al,'0'                  ;any leading zeroes ?
        jne     nozero                  ;noo
        jmp     strip                   ;yeahh, check next
nozero: 
	dec     esi                      ;adjust that back one byte
	lodsb
out:
	mov dl,al
	mov ah,02h
	int 21h
	lodsb
	cmp al,0
	jnz out
	ret
output endp
;=============================================================================================================================================
; Macros
;=============================================================================================================================================
print	macro	message
	mov ah,09h
	mov dx,offset &message&
	int 21h
		endm

crlf	macro 
	mov ah,02h
	mov dl,0Dh
	int 21h
	mov dl,0Ah
	int 21h
		endm

end start