xref: /freebsd-11.0-release/contrib/ofed/management/libibcommon/src/hash.c

/*
 * Copyright (c) 2005 Voltaire Inc.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * 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 THE AUTHORS OR COPYRIGHT HOLDERS
 * 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.
 *
 */

/*
 * By Bob Jenkins, 1996.  bob_jenkins@burtleburtle.net.  You may use this
 * code any way you wish, private, educational, or commercial.  It's free.
 *
 * See http://burtleburtle.net/bob/hash/evahash.html
 * Use for hash table lookup, or anything where one collision in 2^^32 is
 * acceptable.  Do NOT use for cryptographic purposes.
 */

#include <common.h>

#define hashsize(n) ((uint32)1<<(n))
#define hashmask(n) (hashsize(n)-1)


/*
--------------------------------------------------------------------
mix -- mix 3 32-bit values reversibly.
For every delta with one or two bits set, and the deltas of all three
  high bits or all three low bits, whether the original value of a,b,c
  is almost all zero or is uniformly distributed,
* If mix() is run forward or backward, at least 32 bits in a,b,c
  have at least 1/4 probability of changing.
* If mix() is run forward, every bit of c will change between 1/3 and
  2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)
mix() was built out of 36 single-cycle latency instructions in a
  structure that could supported 2x parallelism, like so:
      a -= b;
      a -= c; x = (c>>13);
      b -= c; a ^= x;
      b -= a; x = (a<<8);
      c -= a; b ^= x;
      c -= b; x = (b>>13);
      ...
  Unfortunately, superscalar Pentiums and Sparcs can't take advantage
  of that parallelism.  They've also turned some of those single-cycle
  latency instructions into multi-cycle latency instructions.  Still,
  this is the fastest good hash I could find.  There were about 2^^68
  to choose from.  I only looked at a billion or so.
--------------------------------------------------------------------
*/
#define mix(a,b,c) \
{ \
	a -= b; a -= c; a ^= (c>>13);	\
	b -= c; b -= a; b ^= (a<<8);	\
	c -= a; c -= b; c ^= (b>>13);	\
	a -= b; a -= c; a ^= (c>>12);	\
	b -= c; b -= a; b ^= (a<<16);	\
	c -= a; c -= b; c ^= (b>>5);	\
	a -= b; a -= c; a ^= (c>>3);	\
	b -= c; b -= a; b ^= (a<<10);	\
	c -= a; c -= b; c ^= (b>>15);	\
}

/*
--------------------------------------------------------------------
fhash() -- hash a variable-length key into a 32-bit value
  k       : the key (the unaligned variable-length array of bytes)
  len     : the length of the key, counting by bytes
  initval : can be any 4-byte value
Returns a 32-bit value.  Every bit of the key affects every bit of
the return value.  Every 1-bit and 2-bit delta achieves avalanche.
About 6*len+35 instructions.

The best hash table sizes are powers of 2.  There is no need to do
mod a prime (mod is sooo slow!).  If you need less than 32 bits,
use a bitmask.  For example, if you need only 10 bits, do
  h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.

If you are hashing n strings (uint8 **)k, do it like this:
  for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);

--------------------------------------------------------------------
*/

uint32_t
fhash(uint8_t *k, int length, uint32_t initval)
{
	uint32_t a, b, c, len;

	/* Set up the internal state */
	len = length;
	a = b = 0x9e3779b9;		/* the golden ratio; an arbitrary value */
	c = initval;			/* the previous hash value */

	/* handle most of the key */
	while (len >= 12) {
		a += (k[0] + ((uint32_t)k[1]<<8) +
		      ((uint32_t)k[2]<<16) + ((uint32_t)k[3]<<24));
		b += (k[4] + ((uint32_t)k[5]<<8) + ((uint32_t)k[6]<<16) +
		      ((uint32_t)k[7]<<24));
		c += (k[8] + ((uint32_t)k[9]<<8) + ((uint32_t)k[10]<<16) +
		      ((uint32_t)k[11]<<24));
		mix(a, b, c);
		k += 12; len -= 12;
	}

	/* handle the last 11 bytes */
	c += length;
	switch (len) {		/* all the case statements fall through */
	case 11: c += ((uint32_t)k[10]<<24);
	case 10: c += ((uint32_t)k[9]<<16);
	case 9 : c += ((uint32_t)k[8]<<8);
		/* the first byte of c is reserved for the length */
	case 8 : b += ((uint32_t)k[7]<<24);
	case 7 : b += ((uint32_t)k[6]<<16);
	case 6 : b += ((uint32_t)k[5]<<8);
	case 5 : b += k[4];
	case 4 : a += ((uint32_t)k[3]<<24);
	case 3 : a += ((uint32_t)k[2]<<16);
	case 2 : a += ((uint32_t)k[1]<<8);
	case 1 : a += k[0];
	  /* case 0: nothing left to add */
	}

	mix(a, b, c);

	return c;
}