linux-kernel - Re: [RFC PATCH] crypto: arc4: Implement a version optimized for memory usage

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Date:   Tue, 4 May 2021 09:57:34 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [RFC PATCH] crypto: arc4: Implement a version optimized for
 memory usage

On Sun, May 02, 2021 at 09:29:46PM +0200, Christophe JAILLET wrote:
> +#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +#define S_type	u8
> +#else
> +#define S_type	u32
> +#endif
> +
>  struct arc4_ctx {
> -	u32 S[256];
> +	S_type S[256];
>  	u32 x, y;
>  };

Is it actually useful to keep both versions?  It seems we could just use the u8
version everywhere.  Note that there aren't actually any unaligned memory
accesses, so choosing the version conditionally on
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS seems odd.  What are you trying to
determine by checking that?

- Eric