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Move the overview comment to the top of the file.

This commit is contained in:
Raymond Hettinger 2013-09-07 15:05:00 -07:00
parent 7b4769937f
commit ae7b00e2d3
1 changed files with 20 additions and 22 deletions
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42
Objects/setobject.c
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@ -1,10 +1,30 @@
/* set object implementation
Written and maintained by Raymond D. Hettinger <python@rcn.com>
Derived from Lib/sets.py and Objects/dictobject.c.
Copyright (c) 2003-2013 Python Software Foundation.
All rights reserved.
The basic lookup function used by all operations.
This is based on Algorithm D from Knuth Vol. 3, Sec. 6.4.
The initial probe index is computed as hash mod the table size.
Subsequent probe indices are computed as explained in Objects/dictobject.c.
To improve cache locality, each probe inspects a series of consecutive
nearby entries before moving on to probes elsewhere in memory. This leaves
us with a hybrid of linear probing and open addressing. The linear probing
reduces the cost of hash collisions because consecutive memory accesses
tend to be much cheaper than scattered probes. After LINEAR_PROBES steps,
we then use open addressing with the upper bits from the hash value. This
helps break-up long chains of collisions.
All arithmetic on hash should ignore overflow.
Unlike the dictionary implementation, the lookkey functions can return
NULL if the rich comparison returns an error.
*/
#include "Python.h"
@ -44,28 +64,6 @@ PyObject *_PySet_Dummy = dummy;
static PySetObject *free_list[PySet_MAXFREELIST];
static int numfree = 0;
/*
The basic lookup function used by all operations.
This is based on Algorithm D from Knuth Vol. 3, Sec. 6.4.
The initial probe index is computed as hash mod the table size.
Subsequent probe indices are computed as explained in Objects/dictobject.c.
To improve cache locality, each probe inspects a series of consecutive
nearby entries before moving on to probes elsewhere in memory. This leaves
us with a hybrid of linear probing and open addressing. The linear probing
reduces the cost of hash collisions because consecutive memory accesses
tend to be much cheaper than scattered probes. After LINEAR_PROBES steps,
we then use open addressing with the upper bits from the hash value. This
helps break-up long chains of collisions.
All arithmetic on hash should ignore overflow.
Unlike the dictionary implementation, the lookkey functions can return
NULL if the rich comparison returns an error.
*/
static setentry *
set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
{