Object hash (was: Re: [ANNOUNCE] git-rev-size: calculate sizes of repository)

From: Josef Weidendorfer <josef.weidendorfer@gmx.de>
Date: Aug 20, 2006, 16:37 UTC
Message-ID: <200608201837.33577.Josef.Weidendorfer@gmx.de>
In-Reply-To: <Pine.LNX.4.63.0608201805070.28360@wbgn013.biozentrum.uni-wuerzburg.de>

On Sunday 20 August 2006 18:09, Johannes Schindelin wrote: Hi,

> Most notably, it adds an object hash map structure to the library.

Aside from the given command of this thread, this is interesting (even more interesting would be a persistent cache for arbitrary object data). As this could be used in other contexts, some general comments:

> +static unsigned int hash_index(struct hash_map *hash, const char *sha1)
> +{
> +	unsigned int index = *(unsigned int *)sha1;

If you have the same SHA1, stored at different addresses, you get different indexes for the same SHA1. Index probably should be calculated from the SHA1 string.

> +void hash_put(struct hash_map *hash, struct object *obj)
> +{
> +	if (++hash->nr > hash->alloc / 2)
> +		grow_hash(hash);

If you insert the same object multiple times, hash->nr will get too big.

Josef