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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 __APPLE__
#ifndef uint32_t
typedef unsigned long uint32_t;
#endif
#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