netdev - RE: [PATCH] xfrm: optimize ipv4 selector matching

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6D8AED7@saturn3.aculab.com>
Date:	Tue, 22 Nov 2011 14:50:59 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Alexey Dobriyan" <adobriyan@...il.com>, <davem@...emloft.net>
Cc:	<netdev@...r.kernel.org>
Subject: RE: [PATCH] xfrm: optimize ipv4 selector matching

 
> +static inline int addr4_match(const __be32 a1, const __be32 
> a2, const u8 prefixlen)
> +{
> +	/* C99 6.5.7 (3): u32 << 32 is undefined behaviour */
> +	if (prefixlen == 0) {
> +		/* Matching constants result in smaller assembly. */
> +		return 0xFFFFFFFFu;
> +	}
> +	return !((a1 ^ a2) & htonl(0xFFFFFFFFu << (32 - prefixlen)));
> +}
> +

It would probably be clearer to 'return 1' when prefixlen is zero.

If this is a common path, might be worth caching
    htonl(0xFFFFFFFFu << (32 - prefixlen))
in the enclosing structure.

	David


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