[PATCH 3/3] resolv: Optimize inet_ntop

[Florian Weimer]

* Adhemerval Zanella:

> -static const char *
> +static inline const char *
>  inet_ntop6 (const u_char *src, char *dst, socklen_t size)
>  {
>  	/*
> @@ -108,7 +123,7 @@ inet_ntop6 (const u_char *src, char *dst, socklen_t size)
>  	 */
>  	char tmp[sizeof "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255"], *tp;
>  	struct { int base, len; } best, cur;
> -	u_int words[NS_IN6ADDRSZ / NS_INT16SZ];
> +	uint16_t words[NS_IN6ADDRSZ / NS_INT16SZ] = { 0 };
>  	int i;
>  
>  	/*
> @@ -116,7 +131,6 @@ inet_ntop6 (const u_char *src, char *dst, socklen_t size)
>  	 *	Copy the input (bytewise) array into a wordwise array.
>  	 *	Find the longest run of 0x00's in src[] for :: shorthanding.
>  	 */
> -	memset(words, '\0', sizeof words);
>  	for (i = 0; i < NS_IN6ADDRSZ; i += 2)
>  		words[i / 2] = (src[i] << 8) | src[i + 1];

The words copy shouldn't really be needed, GCC can usually combine two
byte accesses into single 16-bit loads.

It should be possible to optimize put_uint16 using SWAR techniques.  We
don't need to do byte-wise output, either.  We can use full 32-bit
writes, potentially with overlaps.

If the user-supplied output buffer has the maximum possible size, we
don't need the temporary copy.  (This applies to the IPv4 variant, too.)

Thanks,
Florian