python hash() function

Dan Bishop danb_83 at yahoo.com
Wed Mar 26 03:30:05 CET 2008


On Mar 25, 9:22 pm, "Terry Reedy" <tjre... at udel.edu> wrote:
> "Alvin Delagon" <adela... at gmail.com> wrote in message
>
> news:7a01f6c00803251905j4b12633m65b2cde0f3037854 at mail.gmail.com...
> | Hello,
> |
> | >>> hash("foobar")
> | -1969371895
> |
> | Anyone can explain to me how the hash() function in python does its work?
> A
> | link to its source could help me a lot also. I'm looking for a way to
> | replicate this function in php. Thanks in advance.
>
> If not part of your installation, start with svn.python.org and click
> browse.  I would look for builtins.c or somesuch.

It's in 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 = Py_Size(a);
	p = (unsigned char *) a->ob_sval;
	x = *p << 7;
	while (--len >= 0)
		x = (1000003*x) ^ *p++;
	x ^= Py_Size(a);
	if (x == -1)
		x = -2;
	a->ob_shash = x;
	return x;
}



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