Dos box - division 64 bit by 64 bit

[uni.stop]

Hello,
I'm new here and I don't know if it is the right place to post my problem.

How can I implement 64 bit by 64 bit division in Assembly 8086?
I have already enabled extendeed registers with .386 directive.

Thanks!

[dedndave]

well - when you multiply a 32-bit value by another 32-bit value, you end up with as many as 64 bits
the opposite holds true when you divide - sort of   :P

but - the easy answer is to use the FPU
80-bit reals (extended reals) have 64-bits of precision

Ray has a nice tutorial to get you started, as well as a lib and some examples...

http://www.ray.masmcode.com/

[nidud]

deleted

[jcfuller]

Am I missing something here?
The topic says dosbox so I would assume 16bit assembly ???

James

[Gunther]

James,

Am I missing something here?
The topic says dosbox so I would assume 16bit assembly ???

the entire thing is a bit more tricky, because the thread is inside the 64 bit forum. Let's see what the thread starter has to say.

Gunther

[dedndave]

you can use 32-bit instructions in 16-bit code   :P

the real question is - what size is the divisor
larger dividends/quotients is easy enough

[nidud]

deleted

[dedndave]

Code Select Expand

    mov     rax,qwDividend
    xor     rdx,rdx
    div     qwDivisor

:P

[MichaelW]

This seems like an unreasonably difficult assignment for anyone new to programming. The Microsoft RTL function that does this was apparently coded in inline assembly in a naked function, using ~70 32-bit instructions.

[dedndave]

long division is a good assembler exercise   :P