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Date: Wed, 1 Apr 2015 09:53:25 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Shuah Khan <shuahkh@osg.samsung.com>,
        Scott J Norton <scott.norton@hp.com>,
        Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [PATCH] lfsr: a simple binary Galois linear feedback shift
 register
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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.

> +	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.