15 Aug
2001
15 Aug
'01
3:03 p.m.
Sean 'Captain Napalm' Conner skrev:
It was thus said that the Great Iggy Drougge once
stated:
>
> Jeffrey S. Sharp skrev:
>
> >I've always thought that one of the more simple assembly languages would
> >be a great 'first language' for someone wanting to learn how to program.
> >Who's with me?
>
> Most assemblers haven't got a PRINT statement, so, no, I don't think so.
Depends upon the environment. Under AmigaOS you have
RawDoFmt(), which is
part of Exec and available to Assembly language programmers (and it works
similar to C's printf()). Under MS-DOS you have INT 21h, funtion 9, which
prints a text string (ended by a `$'). But all you really need is a way to
print out characters, leaving printing of numeric values as a programming
exercise. In fact, writing a printf()-like routine (no formatting, just
stuff like `%d' and `%s') is fairly simple (6809 code):
Now I'm glad I spent some time in PCDragon's debugger this evening! =)
**********************************************
* PRINTF - a printf()-esque routine.
* Entry: X - ASCIIZ string
* U - user data stack
* Exit: X - end of string
* U - adjusted as data is used
* A - 0
***********************************************
PRFT50 LDA ,X+ ; get next character after %
CMPA #'% ; %?
BEQ PRTF20 ; if so, print it
CMPA #'d ; print a decimal number?
BNE PRTF51
PULU D ; get value
BSR DECOUT ; print it
BRA PRINTF ; continue
PRTF51 CMPA #'x ; print hex number?
BNE PRTF52
PULU D ; get value
BSR HEXOUT ; print hex value
BRA PRINTF
PRTF52 CMPA #'s ; print string?
BNE PRTF20
PSHS X ; save current string
PULU X ; get new string
BSR PRINTF ; print it (oooh! recursion!)
PULS X ; get old string
BRA PRINTF
PRTF10 CMPA #'% ; print data?
BEQ PRFT50 ; if so, handle
PRTF20 JSR CHROUT ; print character
PRINTF LDA ,X+ ; get next character
BNE PRTF10 ; if not NUL, continue
RTS
Now all that's left is writing CHROUT (or assume the system has such a
routine), DECOUT and HEXOUT (HEXOUT is trivial, DECOUT may make some work).
It's all a part of learning.
But you've just served to prove my thesis. A PRINT statement like this will
only scare the newbies away. I remember when I was just getting interested in
computers, nearly ten years ago, when a computer magazine (the great DMz) had
a feature on programming languages (you don't see features like that often
nowadays). Along with a short description of each language, there was an
example program which prompted the user for some data, formatted it and
printed it on the screen. We all know what that would look like in BASIC, most
would be able to whip up a C or Pascal program to the same effect, but the
(m68k) assembly program occupied the entire right column of the page it was
printed on. That certainly instilled a certain kind of respect for assembly
into my young, impressionable mind.
It was only a month or two ago, when a mate showed me how to make a silly
little raster flash effect on a C64 in a few lines of assembly that it finally
dawned upon me that it might not be all about black magic.
No matter how easy it might be to make a PRINT statement in 6809 assembly,
it's still a whole lot of lines compared to PRINT"HELLO WORLD!".
--
En ligne avec Thor 2.6a.
Iggy tipsar: Vill du l?sa en PDF-fil, men saknar l?sare, skicka den till
pdf2txt(a)adobe.com, du f?r den tillbaka som ren ASCII till din epostadress.