From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 28 Apr 2011 20:20:54 GMT
Subject: Re: [PATCH] git gc: Speed it up by 18% via faster hash comparisons
Message-ID: <7v8vuu3z6h.fsf@alter.siamese.dyndns.org>
In-Reply-To: <20110428101902.GA17257@elte.hu>

Ingo Molnar <mingo@elte.hu> writes:

> In any case, i'll retract the null case as it really isnt called that often in 
> the tests i've done - updated patch below - it simply falls back on to hashcmp.
>
> Thanks,
>
> 	Ingo
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>

Thanks, will queue this version.

> diff --git a/cache.h b/cache.h
> index 2674f4c..39fa9cd 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -675,14 +675,24 @@ extern char *sha1_pack_name(const unsigned char *sha1);
>  extern char *sha1_pack_index_name(const unsigned char *sha1);
>  extern const char *find_unique_abbrev(const unsigned char *sha1, int);
>  extern const unsigned char null_sha1[20];
> -static inline int is_null_sha1(const unsigned char *sha1)
> +
> +static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
>  {
> -	return !memcmp(sha1, null_sha1, 20);
> +	int i;
> +
> +	for (i = 0; i < 20; i++, sha1++, sha2++) {
> +		if (*sha1 != *sha2)
> +			return *sha1 - *sha2;
> +	}
> +
> +	return 0;
>  }
> -static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
> +
> +static inline int is_null_sha1(const unsigned char *sha1)
>  {
> -	return memcmp(sha1, sha2, 20);
> +	return !hashcmp(sha1, null_sha1);
>  }
> +
>  static inline void hashcpy(unsigned char *sha_dst, const unsigned char *sha_src)
>  {
>  	memcpy(sha_dst, sha_src, 20);