Re: [PATCH] lfsr: a simple binary Galois linear feedback shift register

[Waiman Long]

On 04/01/2015 03:53 AM, Peter Zijlstra wrote:
> On Tue, Mar 31, 2015 at 01:28:09PM -0400, Waiman Long wrote:
> > +static __always_inline u32 lfsr_taps(int bits)
> > +static inline u32 lfsr(u32 val, int bits)
> > +{
> > +	u32 bit = val&  1;
> > +
> > +	/*
> > +	 * LFSR doesn't work with a start state of 0, so force it to a
> > +	 * non-zero value (bits) as the next state.
> > +	 */
> > +	if (val == 0)
> > +		return bits;
> Arguably this should be a debug/warn instead of a silent modification.

Since it is used in conjunction with hashing, it is possible that 
hashing can produce a value of 0. Do we really want to have a warning 
for that? Alternatively, we can pass in some flag to decide if a warning 
should be issued.

> > +	val>>= 1;
> > +	if (bit)
> > +		val ^= lfsr_taps(bits);
> > +	return val;
> > +}
> I was also thinking that if we modify the hash to be dynamically signed
> we cannot use the compile time tap selection and need to change the
> interface slightly.

So you mean having another argument for the caller to pass in the tap 
value instead of using the default. Right?

-Longman
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/