commit 0ad607d6042e59e8d63a32ddd98a6673ed5f79db Author: Nick Mathewson nickm@torproject.org Date: Tue May 6 12:27:18 2014 -0400

Faster chan_circid_entry_hash implementation

Since this is critical-path, let's tune the value we pass to csiphash a little so it fits into one whole round. --- src/or/circuitlist.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/or/circuitlist.c b/src/or/circuitlist.c index 58fb22d..e5ed9c0 100644 --- a/src/or/circuitlist.c +++ b/src/or/circuitlist.c @@ -76,14 +76,15 @@ chan_circid_entries_eq_(chan_circid_circuit_map_t *a, static INLINE unsigned int chan_circid_entry_hash_(chan_circid_circuit_map_t *a) { - struct { - void *chan; - circid_t circid; - } s; - memset(&s, 0, sizeof(s)); - s.chan = a->chan; - s.circid = a->circ_id; - return (unsigned) siphash24g(&s, sizeof(s)); + /* Try to squeze the siphash input into 8 bytes to save any extra siphash + * rounds. This hash function is in the critical path. */ + uintptr_t chan = (uintptr_t) (void*) a->chan; + uint32_t array[2]; + array[0] = a->circ_id; + /* The low bits of the channel pointer are uninteresting, since the channel + * is a pretty big structure. */ + array[1] = (uint32_t) (chan >> 6); + return (unsigned) siphash24g(array, sizeof(array)); }

/** Map from [chan,circid] to circuit. */