Truly amazing

Robert Prins

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Apr 20, 2021, 10:03:25 AM4/20/21

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Just came across this one:

C4 1C 9F AB 47 47 EB F9

Save as a .COM file and run it, even in DOSBox-X. (Do a CLS before you start it)

Comparable to a gem like "+[>,]+[<.-]" in that language that usually has an '*'
in it's name. ;)

Robert
--
Robert AH Prins
robert(a)prino(d)org
The hitchhiking grandfather - https://prino.neocities.org/indez.html
Some REXX code for use on z/OS - https://prino.neocities.org/zOS/zOS-Tools.html

wolfgang kern

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Apr 20, 2021, 11:03:39 AM4/20/21

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On 20.04.2021 17:55, Robert Prins wrote:
> Just came across this one:
>
> C4 1C 9F AB 47 47 EB F9
>
> Save as a .COM file and run it, even in DOSBox-X. (Do a CLS before you
> start it)
>
> Comparable to a gem like "+[>,]+[<.-]" in that language that usually has
> an '*' in it's name. ;)
>
> Robert

I can't recommend to do this!

endless:
LES BX,[SI] ;SI=?? may depend on environment
LAHF ;who knows what's in the flags ?
STOSW ;WRITE to ES:DI (try to use cc-flags for color)
INC DI dup2 ;stosw does this also
JMP $-7 ;endless or until crash

BX isn't used.
And if SI doesn't point to the screen-seg it writes to another 64KB block.
__
wolfgang

Kerr-Mudd,John

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Apr 21, 2021, 7:28:09 AM4/21/21

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On Tue, 20 Apr 2021 14:52:58 GMT, wolfgang kern
<now...@nospicedham.never.at> wrote:

> On 20.04.2021 17:55, Robert Prins wrote:
>> Just came across this one:
>>
>> C4 1C 9F AB 47 47 EB F9
>>
>> Save as a .COM file and run it, even in DOSBox-X. (Do a CLS before
>> you start it)
>>
>> Comparable to a gem like "+[>,]+[<.-]" in that language that usually
>> has an '*' in it's name. ;)
>>
>> Robert
>
> I can't recommend to do this!
>
> endless:
> LES BX,[SI] ;SI=?? may depend on environment
> LAHF ;who knows what's in the flags ?
> STOSW ;WRITE to ES:DI (try to use cc-flags for color)
> INC DI dup2 ;stosw does this also

skips next scrn char

> JMP $-7 ;endless or until crash
>
> BX isn't used.

except to set es.

> And if SI doesn't point to the screen-seg it writes to another 64KB
> block. __
> wolfgang
>
>

I presume it's meant to put stripes down the screen; but al is 0 at start;
aha! I see the jmp goes to 101, which becomes SBB al,9F

I thought a .COM file at startup has bx=0x0000,si=0x0100,di=0xFFFE,
es=ds=cs;
LES must somehow pick up the Screen seg.

OK it's a mini 'Matrix' tribute. Nice.

--
Bah, and indeed, Humbug.

wolfgang kern

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Apr 26, 2021, 8:45:38 AM4/26/21

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On 21.04.2021 13:12, Kerr-Mudd,John wrote:
> On Tue, 20 Apr 2021 14:52:58 GMT, wolfgang kern
> <now...@nospicedham.never.at> wrote:
>
>> On 20.04.2021 17:55, Robert Prins wrote:
>>> Just came across this one:
>>>
>>> C4 1C 9F AB 47 47 EB F9
>>>
>>> Save as a .COM file and run it, even in DOSBox-X. (Do a CLS before
>>> you start it)
>>>
>>> Comparable to a gem like "+[>,]+[<.-]" in that language that usually
>>> has an '*' in it's name. ;)
>>>
>>> Robert
>>
>> I can't recommend to do this!
>>
>> endless:
>> LES BX,[SI] ;SI=?? may depend on environment
>> LAHF ;who knows what's in the flags ?
>> STOSW ;WRITE to ES:DI (try to use cc-flags for color)
>> INC DI dup2 ;stosw does this also
> skips next scrn char
>
>> JMP $-7 ;endless or until crash
>>
>> BX isn't used.
> except to set es.
>
>> And if SI doesn't point to the screen-seg it writes to another 64KB
>> block.

> I presume it's meant to put stripes down the screen; but al is 0 at start;
> aha! I see the jmp goes to 101, which becomes SBB al,9F

yeah, I saw it but forgot to mention where AL get its value.

> I thought a .COM file at startup has bx=0x0000,si=0x0100,di=0xFFFE,
> es=ds=cs;
> LES must somehow pick up the Screen seg.

if DS:SI points to CS:0100 then ES:BX read as AB9f:1cc4 which is at the
end of in the graphics-RAM range (nothing to see in text mode) but it
overwrites part of the VideoBIOS (it may be RAM-mapped and writable).

> OK it's a mini 'Matrix' tribute. Nice.

I cannot try such here.
__
wolfgang