Re: [patch/rfc 2/4] pcf875x I2C GPIO expander driver

[Jean Delvare <khali@linux-fr.org>]

Hi Bill,

On Fri, 30 Nov 2007 07:04:10 -0600, Bill Gatliff wrote:
> Jean Delvare wrote:
> > !!(value & (1 << offset))
> > is more efficiently written
> > (value >> offset) & 1
> 
> ... but not more efficiently implemented.
> 
> Your version requires code to do the shift on live data at runtime.  
> David's version lets the compiler create the mask once, at compile-time.

I don't understand. How could the compiler create the mask at
compile-time when "offset" is only known at runtime?

Anyway, I just checked and gcc (4.1.2 on x86_86) generates the same
code for both expressions, so there's not much to argue about. David,
feel free to ignore my comment if you prefer your implementation :)

-- 
Jean Delvare