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Made lookdict nearly twice as fast, resulting in a 5% overall 

improvement of pystone.  Vladimir Marangozov.
This commit is contained in:
Guido van Rossum 1997-08-18 21:52:47 +00:00
parent 2da391f387
commit fd7a0b871f
1 changed files with 13 additions and 11 deletions
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24
Objects/dictobject.c
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@ -151,26 +151,25 @@ Subsequent probe indices use the values of x^i in GF(2^n) as an offset,
where x is a root. The initial value is derived from sum, too.
(This version is due to Reimer Behrends, some ideas are also due to
Jyrki Alakuijala.)
Jyrki Alakuijala and Vladimir Marangozov.)
*/
static dictentry *lookdict Py_PROTO((dictobject *, PyObject *, long));
static dictentry *
lookdict(mp, key, hash)
dictobject *mp;
PyObject *key;
long hash;
register long hash;
{
register int i;
register unsigned incr;
register unsigned long sum = (unsigned long) hash;
register dictentry *freeslot = NULL;
register dictentry *freeslot;
register unsigned int mask = mp->ma_size-1;
dictentry *ep0 = mp->ma_table;
register dictentry *ep;
/* We must come up with (i, incr) such that 0 <= i < ma_size
and 0 < incr < ma_size and both are a function of hash */
i = (~sum) & mask;
/* We use ~sum instead if sum, as degenerate hash functions, such
i = (~hash) & mask;
/* We use ~hash instead of hash, as degenerate hash functions, such
as for ints <sigh>, can have lots of leading zeros. It's not
really a performance risk, but better safe than sorry. */
ep = &ep0[i];
@ -178,19 +177,22 @@ lookdict(mp, key, hash)
return ep;
if (ep->me_key == dummy)
freeslot = ep;
else if (ep->me_key == key ||
else {
if (ep->me_key == key ||
(ep->me_hash == hash &&
PyObject_Compare(ep->me_key, key) == 0))
{
return ep;
{
return ep;
}
freeslot = NULL;
}
/* XXX What if PyObject_Compare returned an exception? */
/* Derive incr from sum, just to make it more arbitrary. Note that
incr must not be 0, or we will get into an infinite loop.*/
incr = (sum ^ (sum >> 3)) & mask;
incr = (hash ^ ((unsigned long)hash >> 3)) & mask;
if (!incr)
incr = mask;
if (incr > mask) /* Cycle through GF(2^n)-{0} */
else if (incr > mask) /* Cycle through GF(2^n)-{0} */
incr ^= mp->ma_poly; /* This will implicitly clear the
highest bit */
for (;;) {