24 bit numbers in memory

[Buck Huffman]

Does anybody know how to copy 24-bit numbers to the video memory
in a reasonably fast manner in real mode.

This code kinda works but if you call it too much it'll crash big
time. Windows kicks my program out, and dos does a "SYSTEM HALTED!"

' Set a Pixel in vesa 24 bit mode.(Kinda Like PSet)
SUB VesaPSet (x, y, BYVAL clr AS DWORD)
DIM offset AS LOCAL DWORD
DIM bank AS LOCAL WORD
offset = (Bpsl * y) + (x * Bpp) + yOffset
bank = (offset \ &H10000) ' * wingran
offset = offset - &H10000 * bank
bank = bank * wingran
IF bank <> curBank THEN
curBank = bank
! mov ax, &H4F05
! mov bx, &H0000
! mov dx, curBank
! call dword VidFunc
END IF

'everything before this is tested and works in the other modes.
'so I'm sure the problem is in here somewhere.
IF offset < 65535 THEN
! add offset, 2
! mov ax, &HA000
! mov di, offset
! mov es, ax
! mov ax, clr
! stosb
! mov cl, 8
! db &H66
! sar ax, cl
! sub offset, 2
! stosw
END IF
END SUB

Can anyone see off hand where the error is, and could anyone help
me to eliminate the backward memory write in a fast and clean way.
Any help would be grately appreciated, this has been bugging me
for days.

All this trouble came from trying to convert this basic code to
assembly.
DEF SEG = &HA000
IF offset& < 65535 THEN
POKE offset&+2, BITS?(clr)
SHIFT RIGHT clr, 8
POKEI offset&, BITS??(clr)
END IF
as you can see this also writes the numbers to memory backwards
and is way too slow. but it does work.

if you need to see more of the code just let me know.


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[This message has been edited by Buck Huffman (edited May 02, 2002).]

[Lance Edmonds]

The nature of those critical errors suggests that your code is going outside the bounds and "stepping" on something it shouldn't outside of the VGA memory region.

ASM is not really my bag, but the first thing is to do is to somehow log the ESI addresses to make sure the target pointer address is not going out of bounds... solve that and you most likely have your solution.

Good luck!

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Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Lance Edmonds]

Oh, you might want to do a !CLD sometime before the !STOSB too, otherwise the expected DI increment could turn into a DI decrement.

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Buck Huffman]

Well, I fiddled around with it and this is what I've come up with
so far. You were right Lance, it was walking on memory areas that
were out of bounds.

' Set a Pixel.(Kinda Like PSet)
SUB VesaPSet (x, y, BYVAL clr AS DWORD)
DIM offset AS LOCAL DWORD
DIM bank AS LOCAL WORD
IF x > xRes OR y > yRes OR x < 0 OR y < 0 THEN EXIT SUB
offset = (Bpsl * y) + (x * Bpp) + yOffset
bank = (offset \ &H10000)
offset = offset - &H10000 * bank
IF curBank <> bank THEN
! mov ax, bank
! mul wingran
! mov dx, ax
! mov ax, &H4F05
! mov bx, &H0000
! call dword VidFunc
curBank = bank ;this is way faster than !mov curBank, ax
END IF
! mov ax, &HA000 ; move video segment
! mov es, ax ; into ES
! cld ; clear direction flag, thanks Lance
! mov di, offset ; pixel location into DI
! DB &H66 ;<-allows 32-bit regs in PB/DOS
! mov ax, clr ; color into EAX
! cmp offset, 65535 ; one byte left in bank
! jz disbyt
! stosw ; put low word to video mem first?
! cmp offset, 65534 ; two bytes left bank
! jb endme
! call nxtbnk ; bank switch routine
endme:
! mov cl, 16 ; number of bits to shift
! DB &H66 ; 32-bit reg
! sar ax, cl ; shift the high word into position
! stosb ; send the stray byte to video
! jmp thatsall
disbyt:
! stosb
! call nxtbnk
! mov cl, 8
! DB &H66
! sar ax, cl
! stosw
! jmp thatsall
nxtbnk:
! mov ax, &H4F05
! mov bx, &H0000
! mov dx, curBank
! add dx, wingran
! mov curBank, dx
! call dword VidFunc ; switch to next bank
! mov ax, &HA000 ; re-load the regs
! mov es, ax
! cld
! mov di, 0
! DB &H66
! mov ax, clr
! retn
thatsall:
END SUB

At least this one works, even though it's only a hair faster than
the basic code, and I added some code to pick up the pixels that
cross over bank boundries(that's what caused the memory address
confusion, along with countless other problems). My asm skills are
terrible. I'm just learning and it's slow going. If anyone out
there can see any way to improve this code, I would most truely
appreciate any help I could get. and if I ever get this thing
working right, I'll try to post the code on this site somewhere.

Thanks


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