Fredrik Lundh wrote:
> Mathias Panzenboeck wrote:
>
>> But the question is: *IS* this derived work? I mean, it's not copied
>> code.
>> It's the same hashing-logic, which I learned by watching pythons code.
>
> given that it's only a few lines of code, and there's hardly any other
> way to write those lines if you want to implement the same algorithm,
> I'd say it falls under "fair use". crediting the Python developers in
> the source code should be good enough.
>
> </F>
>
ic. I'll write a mail to the python developers then.
The code in python looks like this (see code underneath), just if someone
what's to know.
I only used the logic of the parts I understand. ;)
Objects/stringobject.c:
static long
string_hash(PyStringObject *a)
{
register Py_ssize_t len;
register unsigned char *p;
register long x;
if (a->ob_shash != -1)
return a->ob_shash;
len = a->ob_size;
p = (unsigned char *) a->ob_sval;
x = *p << 7;
while (--len >= 0)
x = (1000003*x) ^ *p++;
x ^= a->ob_size;
if (x == -1)
x = -2;
a->ob_shash = x;
return x;
}
Objects/dictobject.c:
static dictentry *
lookdict_string(dictobject *mp, PyObject *key, register long hash)
{
register size_t i;
register size_t perturb;
register dictentry *freeslot;
register size_t mask = (size_t)mp->ma_mask;
dictentry *ep0 = mp->ma_table;
register dictentry *ep;
/* Make sure this function doesn't have to handle non-string keys,
including subclasses of str; e.g., one reason to subclass
strings is to override __eq__, and for speed we don't cater to
that here. */
if (!PyString_CheckExact(key)) {
#ifdef SHOW_CONVERSION_COUNTS
++converted;
#endif
mp->ma_lookup = lookdict;
return lookdict(mp, key, hash);
}
i = hash & mask;
ep = &ep0[i];
if (ep->me_key == NULL || ep->me_key == key)
return ep;
if (ep->me_key == dummy)
freeslot = ep;
else {
if (ep->me_hash == hash && _PyString_Eq(ep->me_key, key))
return ep;
freeslot = NULL;
}
/* In the loop, me_key == dummy is by far (factor of 100s) the
least likely outcome, so test for that last. */
for (perturb = hash; ; perturb >>= PERTURB_SHIFT) {
i = (i << 2) + i + perturb + 1;
ep = &ep0[i & mask];
if (ep->me_key == NULL)
return freeslot == NULL ? ep : freeslot;
if (ep->me_key == key
|| (ep->me_hash == hash
&& ep->me_key != dummy
&& _PyString_Eq(ep->me_key, key)))
return ep;
if (ep->me_key == dummy && freeslot == NULL)
freeslot = ep;
}
}
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