Re: [TRIVIAL patch] 2.6.2-rc2 Remove compile warnings from timer.o

[Andrew Morton <akpm@osdl.org>]

Darren Williams <dsw@gelato.unsw.edu.au> wrote:
>
> 
> To allow the ia64 simulator to run correctly on slower machines
> the value of HZ has been defined as 32, this has introduced a compiler
> warning (not that much of issue):
> kernel/timer.c: In function `second_overflow':
> kernel/timer.c:589: warning: right shift count is negative
> kernel/timer.c:592: warning: right shift count is negative
> 
> I asked if the value of HZ could be increased for the simulator in 
> include/asm-ia64/param.h, 
> which was rejected for reasons below.

Well we really should be able to support values lower than 32 anyway - just
from a quality-of-code point of view.

I do recall once spying a piece of code which would cause a div-by-zero if
HZ was set to less than 50.  These things happen.

>      ltemp = time_freq + pps_freq;
> +    
> +#if (SHIFT_SCALE <= (SHIFT_USEC + SHIFT_HZ))
>      if (ltemp < 0)
>  	time_adj -= -ltemp >>
>  	    (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
>      else
>  	time_adj += ltemp >>
>  	    (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
> +	    
> +#else	/* (SHIFT_SCALE > (SHIFT_USEC + SHIFT_HZ)) */
> +    if (ltemp < 0)
> +	time_adj -= -ltemp >> SHIFT_SCALE;
> +    else
> +	time_adj += ltemp >> SHIFT_SCALE;
> +	    
> +#endif /* (SHIFT_SCALE > (SHIFT_USEC + SHIFT_HZ)) */

You should lose the ifdefs.  Just do:

	if (SHIFT_SCALE <= (SHIFT_USEC + SHIFT_HZ)) {
		if (ltemp < 0)
			time_adj -= -ltemp >>
				(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
		else
			time_adj += ltemp >>
				(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
	}
	...

because

a) It is not revolting and

b) The compiler checks the unused code for you, then throws it away.