linux-kernel - Re: [PATCH 2/2] MPILIB: Deobfuscate mpi

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Date:	Fri, 09 Jan 2015 11:00:23 +0000
From:	David Howells <dhowells@...hat.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	dhowells@...hat.com, Rusty Russell <rusty@...tcorp.com.au>,
	d.kasatkin@...sung.com, linux-kernel@...r.kernel.org,
	keyrings@...ux-nfs.org
Subject: Re: [PATCH 2/2] MPILIB: Deobfuscate mpi_cmp

This looks very reasonable.  cc'ing Dmitry for his check.

David
---
Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> The condition preceding 'return 1;' makes my head hurt. At this point,
> we know that u and v have the same sign; if they are negative, they
> compare opposite to how their absolute values compare (which
> mpihelp_cmp found for us), otherwise cmp itself is the
> answer. Negating cmp is ok since mpihelp_cmp returns {-1,0,1};
> -INT_MIN==INT_MIN won't bite us.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  lib/mpi/mpi-cmp.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/mpi/mpi-cmp.c b/lib/mpi/mpi-cmp.c
> index 3801694240d8..d25e9e96c310 100644
> --- a/lib/mpi/mpi-cmp.c
> +++ b/lib/mpi/mpi-cmp.c
> @@ -61,10 +61,8 @@ int mpi_cmp(MPI u, MPI v)
>  	if (!usize)
>  		return 0;
>  	cmp = mpihelp_cmp(u->d, v->d, usize);
> -	if (!cmp)
> -		return 0;
> -	if ((cmp < 0 ? 1 : 0) == (u->sign ? 1 : 0))
> -		return 1;
> -	return -1;
> +	if (u->sign)
> +		return -cmp;
> +	return cmp;
>  }
>  EXPORT_SYMBOL_GPL(mpi_cmp);
> -- 
> 2.1.3
--
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