Prev: Check out
Next: Detecting A20 gate
From: Rod Pemberton on 30 May 2010 05:22
"Rod Pemberton" <do_not_have(a)notreplytome.cmm> wrote in message
news:htta9t$qlm$1(a)speranza.aioe.org...
> "Frank Kotler" <fbkotler(a)myfairpoint.net> wrote in message
> news:htt678$m3i$1(a)speranza.aioe.org...
> > Rod Pemberton wrote:
> > > "Frank Kotler" <fbkotler(a)myfairpoint.net> wrote in message
> > > news:hto6nn$soc$1(a)speranza.aioe.org...
> > >> Naw, we're just printing the bytes in "reversed order" - high nybble
of
> > >> edx first, low nybble of eax last. Since we "get" them al-first,
> > >> Nathan's setting the direction flag to start at the "end" of the
> buffer,
> > >> and work toward the "front".
> > >>
> > >
> > > Sorry, I didn't look at the routine... Can't he just change the
> starting
> > > position and direction of the print on the screen, instead of the
order
> of
> > > the byte processing via DF? I.e., print byte to the right, move left
a
> > > char, print next byte, etc.
> >
> > I guess you could do that. How would you do it?
>
> Me? Direct write to the PC's text screen (mode 3), unless an OS is in my
> way.
>
> For 16-bit, ES set to b800h, BX set to screen location, using ES as
override
> on mov byte to BX. Bust word into nybbles in AL and AH.
>

Sorry, bust word into bytes, then bust bytes into nybbles in AL and AH for
ASCII adjustment and printing.

> For 32-bit, EBX set to screen location, lea to add in B8000h to ebx, mov
> byte to EBX. Bust dword into nybbles in AL, AH, CL, CH.
>

Sorry, bust dword into bytes, then bust bytes into nybbles in AL, AH, CL, CH
for ASCII adjustment and printing.

> Inc/dec BX or EBX as needed. Since byte sized moves, allows you to write
> color info inbetween.
>
> > Another way to deal with the "bytes in wrong order" problem is to store
> > 'em in the buffer "as they come" and do a "revstring" on it before
> > printing.
>
> That works.
>
> > Or push 'em on the stack and pop 'em off in the "right" order.
>
> That works too. And, you don't need a string routine. DAS, DAA is 64-bit
> obsoleted. Did you guys already consider BSWAP or XCHG to reverse the
byte
> order?
>
> > I thought Nathan's approach of using std/cld worked out pretty well...
> >
>
> I vaguely recall some sort of issue with using rep movs in reverse
order...
> RBIL bugslist?
>
>
> Rod Pemberton

RP


 | 
Pages: 1
Prev: Check out
Next: Detecting A20 gate