asdk-libdrm

/* xf86drmHash.c -- Small hash table support for integer -> integer mapping

 * Created: Sun Apr 18 09:35:45 1999 by faith@precisioninsight.com

 *

 * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.

 * All Rights Reserved.

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * copy of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, copy, modify, merge, publish, distribute, sublicense,

 * and/or sell copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice (including the next

 * paragraph) shall be included in all copies or substantial portions of the

 * Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL

 * PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR

 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,

 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

 * DEALINGS IN THE SOFTWARE.

 *

 * Authors: Rickard E. (Rik) Faith <faith@valinux.com>

 *

 * DESCRIPTION

 *

 * This file contains a straightforward implementation of a fixed-sized

 * hash table using self-organizing linked lists [Knuth73, pp. 398-399] for

 * collision resolution.  There are two potentially interesting things

 * about this implementation:

 *

 * 1) The table is power-of-two sized.  Prime sized tables are more

 * traditional, but do not have a significant advantage over power-of-two

 * sized table, especially when double hashing is not used for collision

 * resolution.

 *

 * 2) The hash computation uses a table of random integers [Hanson97,

 * pp. 39-41].

 *

 * FUTURE ENHANCEMENTS

 *

 * With a table size of 512, the current implementation is sufficient for a

 * few hundred keys.  Since this is well above the expected size of the

 * tables for which this implementation was designed, the implementation of

 * dynamic hash tables was postponed until the need arises.  A common (and

 * naive) approach to dynamic hash table implementation simply creates a

 * new hash table when necessary, rehashes all the data into the new table,

 * and destroys the old table.  The approach in [Larson88] is superior in

 * two ways: 1) only a portion of the table is expanded when needed,

 * distributing the expansion cost over several insertions, and 2) portions

 * of the table can be locked, enabling a scalable thread-safe

 * implementation.

 *

 * REFERENCES

 *

 * [Hanson97] David R. Hanson.  C Interfaces and Implementations:

 * Techniques for Creating Reusable Software.  Reading, Massachusetts:

 * Addison-Wesley, 1997.

 *

 * [Knuth73] Donald E. Knuth. The Art of Computer Programming.  Volume 3: