Tim Peters <[email protected]> added the comment:
As a sanity check, I tried the 32-bit version of MurmurHash2 (version 3 doesn't
have a 32-bit version). All of my Python tests had collisions, and while the
new tuple test dropped to 15, product([0.5, 0.25], repeat=20) skyrocketed from
141 (32-bit xxHash) to 3848.
I could live with that too, but xxHash does better overall on our tiny tests,
and requires less code and fewer cycles.
Here's what I used:
static Py_hash_t
tuplehash(PyTupleObject *v)
{
const Py_uhash_t m = 0x5bd1e995;
const int r = 24;
Py_uhash_t x, t; /* Unsigned for defined overflow behavior. */
Py_hash_t y;
Py_ssize_t len = Py_SIZE(v);
PyObject **p;
x = 0x345678UL ^ (Py_uhash_t)len;
p = v->ob_item;
while (--len >= 0) {
y = PyObject_Hash(*p++);
if (y == -1)
return -1;
Py_uhash_t t = (Py_uhash_t)y;
t *= m;
t ^= t >> r;
t *= m;
x *= m;
x ^= t;
}
x ^= x >> 13;
x *= m;
x ^= x >> 15;
if (x == (Py_uhash_t)-1)
x = -2;
return x;
}
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Python tracker <[email protected]>
<https://bugs.python.org/issue34751>
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