@@ -47,16 +47,13 @@ static hashtab_t cil_strpool_tab = NULL;
static unsigned int cil_strpool_hash(hashtab_t h, const_hashtab_key_t key)
{
- const char *p;
- size_t size;
- unsigned int val;
+ unsigned int hash = 5381;
+ unsigned char c;
- val = 0;
- size = strlen(key);
- for (p = key; ((size_t) (p - key)) < size; p++)
- val =
- (val << 4 | (val >> (8 * sizeof(unsigned int) - 4))) ^ (*p);
- return val & (h->size - 1);
+ while ((c = *(unsigned const char *)key++))
+ hash = ((hash << 5) + hash) ^ c;
+
+ return hash & (h->size - 1);
}
static int cil_strpool_compare(hashtab_t h __attribute__ ((unused)), const_hashtab_key_t key1, const_hashtab_key_t key2)
The hash table implementation uses `& (h->size - 1)` to truncate generated hashes to the number of buckets. This operation is equal to `% h->size` if and only if the size is a power of two (which seems to be always the case). One property of the binary and with a power of two (and probably a small one <=2048) is all higher bits are discarded. Thus a hash function is needed with a good avalanche effect, which the current one is not. Benchmark of building dssp5: # Current Time (mean ± σ): 1.347 s ± 0.065 s [User: 1.207 s, System: 0.138 s] Range (min … max): 1.274 s … 1.436 s 10 runs # Patch Time (mean ± σ): 1.336 s ± 0.029 s [User: 1.195 s, System: 0.140 s] Range (min … max): 1.303 s … 1.376 s 10 runs Signed-off-by: Christian Göttsche <cgzones@googlemail.com> --- libsepol/cil/src/cil_strpool.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)