Hi,
On Sun, 20 Aug 2006, Josef Weidendorfer wrote:
> On Sunday 20 August 2006 18:09, Johannes Schindelin wrote:
>
> > +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.
Actually, it does! "*(unsigned int *)sha1" means that the first 4 bytes
of the sha1 are interpreted as a number.
> > +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.
First, you cannot put the same object multiple times. That is not what a
hash does (at least in this case): it stores unique objects (identified by
their sha1 in this case). If you put another object with the same sha1,
the first will be replaced.
Second, since you call hash_put() once per object, hash->nr cannot grow
too big, because grow_hash() doubles hash->alloc. And I call grow_hash()
once the hash map is half-full; Somebody once told me that would be the
optimal growing strategy.
Ciao,
Dscho
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