Re: [PATCH 2/6] b43: N-PHY: add RSSI functions: poll and set 2055 vcm

[Michael Buesch <mb@bu3sch.de>]

On Monday 11 January 2010 01:27:48 Larry Finger wrote:
> On 01/10/2010 04:32 PM, Michael Buesch wrote:
> > On Sunday 10 January 2010 23:13:20 Rafał Miłecki wrote:
> >> +		buf[0] += (s8)(((s[0] & 0x3F) << 2) >> 2);
> >> +		buf[1] += (s8)((((s[0] >> 8) & 0x3F) << 2) >> 2);
> >> +		buf[2] += (s8)(((s[1] & 0x3F) << 2) >> 2);
> >> +		buf[3] += (s8)((((s[1] >> 8) & 0x3F) << 2) >> 2);
> > 
> > I suggest buf[3] += (s8)((((s[1] >> 8) & 0x3F) << 2) >> 2) << 2) >> 2) << 2) >> 2) << 2) >> 2) << 2) >> 2) << 2) >> 2) << 2) >> 2)
> > ;)
> > No, seriously, why shift left and then shift right? Is this a translation error?
> > I _guess_ it's some mistranslation of the sign extension going on.
> > Or alternatively a compiler going insane on sign extension.
> > 
> > The question is: Do we want these integers to be signextended or not?
> > 
> > What we currently do is this:
> > buf[3] += (s8)((s[1] >> 8) & 0x3F);
> > 
> > which will always result in a positive 8bit integer, as far as I can see.
> > Which smells fishy.
> 
> We do want sign extension of the signed 6-bit quantities into an 8-bit word. The
> translation is correct. Do you know of a better way to extend the signs?

Well, I think you got the parenthesis and cast wrong then.
I think what we want is the following:

+		buf[3] += (s8)(((s[1] >> 8) & 0x3F) << 2) >> 2;

The code is different and the specs, too.

-- 
Greetings, Michael.