[PATCH] b43-asm, b43-dasm: Add 5 new instructions.

[francesco.gringoli at ing.unibs.it]

On Sep 12, 2011, at 12:35 PM, Michael Büsch wrote:

> On Mon, 12 Sep 2011 12:09:01 +0200
> francesco.gringoli at ing.unibs.it wrote:
> 
>> but trying on a = 0x8000 and b = 0x7fff helped me understanding. a - b = 0x8000 + 2'(0x7fff) = 0x0001 > 0. While 0x8000 < 0x7fff.
> 
> I don't get it.
> Can you write simple pseudocode for your instruction?
Will try for jdn.

> For example, for jls, we have this pseudocode:
> 
> if (xxx < yyy)
>    pc := jjj
> (where xxx and yyy are two's complement)
> 

** jump if difference is negative

0d6 xxx yyy jjj

if ( xxx - yyy < 0 )
	pc := jjj

C-pseudocode for jdn

	short c = xxx - yyy;
	if ( c < 0 )
		goto jjj;

Pay attention: it's not equivalent to

	if( xxx - yyy < 0 )
		goto jjj;

Try this simple code:

int main()
{
	short a = 0x8000;
	short b = 0x7fff;
	short c = a - b;
	printf("%d <=> %d\n", a < b, c < 0);
}

I ' ' think ' ' these instructions are useful and ' ' someone ' ' could use them to check time elapsing in a more efficient way (single instruction rather than a couple.

Regards,
-Francesco

> What does jdX do in C-pseudocode?
> 
> http://bcm-v4.sipsolutions.net/802.11/Microcode
> 
> -- 
> Greetings, Michael.