A86 Assembler - Re: newbie: MUL product

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Re: newbie: MUL product

João Jerónimo

2007-07-09, 9:57 pm

Rob Hoelz wrote:
> Here's some code to move the product in DX:AX to EBX. (I'm a newbie as
> well, so feel free to point out errors in my code)
>
> ; This is using NASM syntax
>
> movzx ebx, dx
> sal ebx, 16
> and eax, 0xffff ; Not sure if this is needed
> or ebx, eax

I usually do as follows:
mov bx, dx
shl ebx, 16
mov bx, ax

Zero extends are usually slower than simple copies, and simple shifts are,
I think, faster than arithmetic shifts.

Besides, my version is only 3 instructions long... :-)

JJ

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