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Faster chan_circid_entry_hash implementation

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Since this is critical-path, let's tune the value we pass to
csiphash a little so it fits into one whole round.
This commit is contained in:
Nick Mathewson 2014-05-06 12:27:18 -04:00
parent 8127f4db30
commit 0ad607d604
1 changed files with 9 additions and 8 deletions
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17
src/or/circuitlist.c
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@ -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. */