;****************************************************************************
; D2H displays a decimal number in hexadecimal format. Its syntax is:
;
; D2H decimal-value
;
; where "decimal-value" is a decimal value from 0 to 4,294,967,295.
;****************************************************************************
code segment
assume cs:code,ds:code
org 100h
begin: jmp main
helpmsg db "Displays a decimal number in hexadecimal format."
db 13,10,13,10
db "D2H decimal-value",13,10,"$"
errmsg1 db "Syntax: H2D decimal-value",13,10,"$"
errmsg2 db "Invalid digit",13,10,"$"
errmsg3 db "Number too large (cannot exceed 4,294,967,295)"
crlf db 13,10,"$"
ten dw 10 ;Base 10 multiplier
sixteen dw 16 ;Base 16 divisor
loword dw 0 ;Accumulator (low word)
hiword dw 0 ;Accumulator (high word)
;****************************************************************************
; Procedure MAIN
;****************************************************************************
main proc near
cld ;Clear direction flag
mov si,81h ;Point SI to the command line
call scanhelp ;Scan for a "/?" switch
jnc main1 ;Branch if not found
mov ah,09h ;Display help text
mov dx,offset helpmsg
int 21h
jmp exit ;Exit
main1: call findchar ;Find the start of the string
jc error1 ;Error if there is no string
main2: lodsb ;Get the next digit
cmp al,"," ;Ignore commas
je main2
cmp al,20h ;Exit if it's a space, tab,
je main4 ;or end-of-line character
cmp al,09h
je main4
cmp al,0Dh
je main4
cmp al,"0" ;Error if digit is invalid
jb error2
cmp al,"9"
ja error2
xor ah,ah ;Byte to word in AX
sub al,"0" ;Convert ASCII to binary
push ax ;Save result for later
mov ax,loword ;Add the digit to what
mul ten ;we've already accumulated
push dx
mov bx,ax ;Low word
mov ax,hiword
mul ten
jo error3
pop dx
add ax,dx
jc error4
mov cx,ax ;High word
pop ax
add bx,ax
adc cx,0
jc error5
mov loword,bx
mov hiword,cx
jmp main2
main4: mov bx,loword ;Display the number in
mov ax,hiword ;hex format
call bin2hex
exit: mov ax,4C00h ;Return to DOS
int 21h
;
; Error handling routines.
;
error1: mov dx,offset errmsg1
jmp short error
error2: mov dx,offset errmsg2
jmp short error
error3: add sp,2
error4: add sp,2
error5: mov dx,offset errmsg3
error: mov ah,09h
int 21h
jmp exit
main endp
;****************************************************************************
; BIN2HEX displays the number in AX:BX in hexadecimal format.
;****************************************************************************
bin2hex proc near
xor cx,cx
b2h1: xor dx,dx
div sixteen
mov si,ax
mov ax,bx
div sixteen
mov bx,ax
mov ax,si
inc cx
push dx
or ax,ax
jnz b2h1
or bx,ax
jnz b2h1
b2h2: mov ah,02h
pop dx
add dl,"0"
cmp dl,"9"
jbe b2h3
add dl,7
b2h3: int 21h
loop b2h2
mov ah,09h
mov dx,offset crlf
int 21h
ret
bin2hex endp
;****************************************************************************
; FINDCHAR advances SI to the next non-white-space character. On return,
; carry set indicates EOL was encountered; carry clear indicates it was not.
;****************************************************************************
findchar proc near
lodsb ;Get the next character
cmp al,09h ;Loop if tab
je findchar
cmp al,20h ;Loop if space
je findchar
cmp al,2Ch ;Loop if comma
je findchar
dec si ;Point SI to the character
cmp al,0Dh ;Exit with carry set if end
je eol ;of line is reached
clc ;Clear carry and exit
ret
eol: stc ;Set carry and exit
ret
findchar endp
;****************************************************************************
; SCANHELP scans the command line for a /? switch. If the switch is found,
; carry returns set and SI contains the switch offset. If the switch is not
; found, carry returns clear.
;****************************************************************************
scanhelp proc near
push si ;Save SI
scanloop: lodsb ;Get a character
cmp al,0Dh ;Exit if end of line
je scan_exit
cmp al,"?" ;Loop if not "?"
jne scanloop
cmp byte ptr [si-2],"/" ;Loop if not "/"
jne scanloop
add sp,2 ;Clear the stack
sub si,2 ;Adjust SI
stc ;Set carry and exit
ret
scan_exit: pop si ;Restore SI
clc ;Clear carry and exit
ret
scanhelp endp
code ends
end begin
