On Fri, Aug 18, 2023 at 11:12 AM Christian Göttsche
<cgzones@xxxxxxxxxxxxxx> wrote:
>
> The number of buckets is calculated by performing a binary AND against
> the mask of the hash table, which is one less than its size (which is a
> power of two). This leads to all top bits being discarded, requiring
> for short or similar inputs a hash function with a good avalanche
> effect.
>
> Use djb2a:
>
> # current
> common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11
> classes: 134 entries and 100/256 buckets used, longest chain length 5, sum of chain length^2 234
> roles: 15 entries and 6/16 buckets used, longest chain length 5, sum of chain length^2 57
> types: 4448 entries and 3016/8192 buckets used, longest chain length 41, sum of chain length^2 14922
> users: 7 entries and 3/8 buckets used, longest chain length 3, sum of chain length^2 17
> bools: 306 entries and 221/512 buckets used, longest chain length 4, sum of chain length^2 524
> levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1
> categories: 1024 entries and 400/1024 buckets used, longest chain length 4, sum of chain length^2 2740
>
> # patch
> common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11
> classes: 134 entries and 101/256 buckets used, longest chain length 3, sum of chain length^2 210
> roles: 15 entries and 9/16 buckets used, longest chain length 3, sum of chain length^2 31
> types: 4448 entries and 3459/8192 buckets used, longest chain length 5, sum of chain length^2 6778
> users: 7 entries and 5/8 buckets used, longest chain length 3, sum of chain length^2 13
> bools: 306 entries and 236/512 buckets used, longest chain length 5, sum of chain length^2 470
> levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1
> categories: 1024 entries and 518/1024 buckets used, longest chain length 7, sum of chain length^2 2992
>
> Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
> ---
> security/selinux/ss/symtab.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/security/selinux/ss/symtab.c b/security/selinux/ss/symtab.c
> index 43d7f0319ccd..b6761b96eee4 100644
> --- a/security/selinux/ss/symtab.c
> +++ b/security/selinux/ss/symtab.c
> @@ -11,16 +11,14 @@
>
> static unsigned int symhash(const void *key)
> {
> - const char *p, *keyp;
> - unsigned int size;
> - unsigned int val;
> -
> - val = 0;
> - keyp = key;
> - size = strlen(keyp);
> - for (p = keyp; (p - keyp) < size; p++)
> - val = (val << 4 | (val >> (8*sizeof(unsigned int)-4))) ^ (*p);
> - return val;
> + /* djb2a */
Do we need/want something that specifies the author/license (I assume
public domain) of this code?
> + unsigned int hash = 5381;
> + unsigned char c;
> +
> + while ((c = *(const unsigned char *)key++))
> + hash = ((hash << 5) + hash) ^ c;
> +
> + return hash;
> }
>
> static int symcmp(const void *key1, const void *key2)
> --
> 2.40.1
>
