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/*

 * -------------------------------------------------------------------------------

 * lookup3.c, by Bob Jenkins, May 2006, Public Domain.

 *

 * These are functions for producing 32-bit hashes for hash table lookup.

 * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()

 * are externally useful functions.  Routines to test the hash are included

 * if SELF_TEST is defined.  You can use this free for any purpose.  It's in

 * the public domain.  It has no warranty.

 *

 * You probably want to use hashlittle().  hashlittle() and hashbig()

 * hash byte arrays.  hashlittle() is is faster than hashbig() on

 * little-endian machines.  Intel and AMD are little-endian machines.

 * On second thought, you probably want hashlittle2(), which is identical to

 * hashlittle() except it returns two 32-bit hashes for the price of one.

 * You could implement hashbig2() if you wanted but I haven't bothered here.

 *

 * If you want to find a hash of, say, exactly 7 integers, do

 *  a = i1;  b = i2;  c = i3;

 *  mix(a,b,c);

 *  a += i4; b += i5; c += i6;

 *  mix(a,b,c);

 *  a += i7;

 *  final(a,b,c);

 * then use c as the hash value.  If you have a variable length array of

 * 4-byte integers to hash, use hashword().  If you have a byte array (like

 * a character string), use hashlittle().  If you have several byte arrays, or

 * a mix of things, see the comments above hashlittle().

 *

 * Why is this so big?  I read 12 bytes at a time into 3 4-byte integers,

 * then mix those integers.  This is fast (you can do a lot more thorough

 * mixing with 12*3 instructions on 3 integers than you can with 3 instructions

 * on 1 byte), but shoehorning those bytes into integers efficiently is messy.

 * -------------------------------------------------------------------------------

 */

#ifndef __LOOKUP3_H__

#define __LOOKUP3_H__

#ifndef uint32_t

	typedef unsigned long uint32_t;

#endif

#ifndef uint8_t

	typedef unsigned char uint8_t;

#endif

/*

 * --------------------------------------------------------------------

 * This works on all machines.  To be useful, it requires

 * -- that the key be an array of uint32_t's, and

 * -- that the length be the number of uint32_t's in the key

 *

 * The function hashword() is identical to hashlittle() on little-endian

 * machines, and identical to hashbig() on big-endian machines,

 * except that the length has to be measured in uint32_ts rather than in

 * bytes.  hashlittle() is more complicated than hashword() only because

 * hashlittle() has to dance around fitting the key bytes into registers.

 * --------------------------------------------------------------------

 */

uint32_t hashword(

	const uint32_t *k,                   /* the key, an array of uint32_t values */

	size_t          length,               /* the length of the key, in uint32_ts */

	uint32_t        initval);         /* the previous hash, or an arbitrary value */

/*

 * --------------------------------------------------------------------

 * hashword2() -- same as hashword(), but take two seeds and return two

 * 32-bit values.  pc and pb must both be nonnull, and *pc and *pb must

 * both be initialized with seeds.  If you pass in (*pb)==0, the output

 * (*pc) will be the same as the return value from hashword().

 * --------------------------------------------------------------------

 */

void hashword2 (

	const uint32_t *k,                   /* the key, an array of uint32_t values */

	size_t          length,               /* the length of the key, in uint32_ts */

	uint32_t       *pc,                      /* IN: seed OUT: primary hash value */

	uint32_t       *pb);               /* IN: more seed OUT: secondary hash value */

/*

 * -------------------------------------------------------------------------------

 * hashlittle() -- hash a variable-length key into a 32-bit value

 *  k       : the key (the unaligned variable-length array of bytes)

 *  length  : 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.  Two keys differing by one or two bits will have

 * totally different hash values.

 *

 * 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_t **)k, do it like this:

 *  for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);

 *

 * By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this

 * code any way you wish, private, educational, or commercial.  It's free.

 *

 * Use for hash table lookup, or anything where one collision in 2^^32 is

 * acceptable.  Do NOT use for cryptographic purposes.

 * -------------------------------------------------------------------------------

 */

uint32_t hashlittle( const void *key, size_t length, uint32_t initval);

/*

 * hashlittle2: return 2 32-bit hash values

 *

 * This is identical to hashlittle(), except it returns two 32-bit hash

 * values instead of just one.  This is good enough for hash table

 * lookup with 2^^64 buckets, or if you want a second hash if you're not

 * happy with the first, or if you want a probably-unique 64-bit ID for

 * the key.  *pc is better mixed than *pb, so use *pc first.  If you want

 * a 64-bit value do something like "*pc + (((uint64_t)*pb)<<32)".

 */

void hashlittle2(

	const void *key,       /* the key to hash */

	size_t      length,    /* length of the key */

	uint32_t   *pc,        /* IN: primary initval, OUT: primary hash */

	uint32_t   *pb);       /* IN: secondary initval, OUT: secondary hash */

/*

 * hashbig():

 * This is the same as hashword() on big-endian machines.  It is different

 * from hashlittle() on all machines.  hashbig() takes advantage of

 * big-endian byte ordering.

 */

uint32_t hashbig( const void *key, size_t length, uint32_t initval);

#endif