Subject: Re: [PATCH net-next 1/7] timecounter: provide a macro to initialize the cyclecounter mask field.

From: Richard Cochran <[email-masked]>
Date: Mon, 5 Jan 2015 14:43:27 +0100

On Mon, Jan 05, 2015 at 01:20:57PM +0000, David Laight wrote:
> > +/* simplify initialization of mask field */
> > +#define CYCLECOUNTER_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
> 
> That has me chasing through the C integer promotion rules.
> Better might be:
> 	((bits) < 64 ? (1ULL << (bits)) - 1 : (((1ULL << 63) - 1) << 1) + 1)
> I actually suspect there is a standard definition somewhere?

This is an exact copy of CLOCKSOURCE_MASK, and if wrong, then both are
wrong.  In any case, I can't see any issue here. Is not

	(some_int_type) -1

always equal to

	0xf...(width of type)

for all integer types, when using 2s compliment?

Thanks
Richard