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#ifndef _JHASH_H
#define _JHASH_H
/*
* jhash.h
*
* Example hash function.
*
* Copyright 2009-2012 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
*
* THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
* OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
*
* Permission is hereby granted to use or copy this program for any
* purpose, provided the above notices are retained on all copies.
* Permission to modify the code and to distribute modified code is
* granted, provided the above notices are retained, and a notice that
* the code was modified is included with the above copyright notice.
*/
/*
* Hash function
* Source: http://burtleburtle.net/bob/c/lookup3.c
* Originally Public Domain
*/
#define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
#define mix(a, b, c) \
do { \
a -= c; a ^= rot(c, 4); c += b; \
b -= a; b ^= rot(a, 6); a += c; \
c -= b; c ^= rot(b, 8); b += a; \
a -= c; a ^= rot(c, 16); c += b; \
b -= a; b ^= rot(a, 19); a += c; \
c -= b; c ^= rot(b, 4); b += a; \
} while (0)
#define final(a, b, c) \
{ \
c ^= b; c -= rot(b, 14); \
a ^= c; a -= rot(c, 11); \
b ^= a; b -= rot(a, 25); \
c ^= b; c -= rot(b, 16); \
a ^= c; a -= rot(c, 4); \
b ^= a; b -= rot(a, 14); \
c ^= b; c -= rot(b, 24); \
}
#if (BYTE_ORDER == LITTLE_ENDIAN)
#define HASH_LITTLE_ENDIAN 1
#else
#define HASH_LITTLE_ENDIAN 0
#endif
/*
*
* 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.
*/
static
uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
{
uint32_t a, b, c; /* internal state */
union {
const void *ptr;
size_t i;
} u;
/* Set up the internal state */
a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
u.ptr = key;
if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
const uint32_t *k = (const uint32_t *) key; /* read 32-bit chunks */
/*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
while (length > 12) {
a += k[0];
b += k[1];
c += k[2];
mix(a, b, c);
length -= 12;
k += 3;
}
/*----------------------------- handle the last (probably partial) block */
/*
* "k[2]&0xffffff" actually reads beyond the end of the string, but
* then masks off the part it's not allowed to read. Because the
* string is aligned, the masked-off tail is in the same word as the
* rest of the string. Every machine with memory protection I've seen
* does it on word boundaries, so is OK with this. But VALGRIND will
* still catch it and complain. The masking trick does make the hash
* noticably faster for short strings (like English words).
*/
#ifndef VALGRIND
switch (length) {
case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
case 8 : b+=k[1]; a+=k[0]; break;
case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
case 6 : b+=k[1]&0xffff; a+=k[0]; break;
case 5 : b+=k[1]&0xff; a+=k[0]; break;
case 4 : a+=k[0]; break;
case 3 : a+=k[0]&0xffffff; break;
case 2 : a+=k[0]&0xffff; break;
case 1 : a+=k[0]&0xff; break;
case 0 : return c; /* zero length strings require no mixing */
}
#else /* make valgrind happy */
{
const uint8_t *k8;
k8 = (const uint8_t *) k;
switch (length) {
case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
case 10: c+=((uint32_t) k8[9])<<8; /* fall through */
case 9 : c+=k8[8]; /* fall through */
case 8 : b+=k[1]; a+=k[0]; break;
case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
case 6 : b+=((uint32_t) k8[5])<<8; /* fall through */
case 5 : b+=k8[4]; /* fall through */
case 4 : a+=k[0]; break;
case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
case 2 : a+=((uint32_t) k8[1])<<8; /* fall through */
case 1 : a+=k8[0]; break;
case 0 : return c;
}
}
#endif /* !valgrind */
} else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
const uint16_t *k = (const uint16_t *) key; /* read 16-bit chunks */
const uint8_t *k8;
/*--------------- all but last block: aligned reads and different mixing */
while (length > 12)
{
a += k[0] + (((uint32_t) k[1])<<16);
b += k[2] + (((uint32_t) k[3])<<16);
c += k[4] + (((uint32_t) k[5])<<16);
mix(a, b, c);
length -= 12;
k += 6;
}
/*----------------------------- handle the last (probably partial) block */
k8 = (const uint8_t *) k;
switch(length)
{
case 12: c+=k[4]+(((uint32_t) k[5])<<16);
b+=k[2]+(((uint32_t) k[3])<<16);
a+=k[0]+(((uint32_t) k[1])<<16);
break;
case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
case 10: c+=k[4];
b+=k[2]+(((uint32_t) k[3])<<16);
a+=k[0]+(((uint32_t) k[1])<<16);
break;
case 9 : c+=k8[8]; /* fall through */
case 8 : b+=k[2]+(((uint32_t) k[3])<<16);
a+=k[0]+(((uint32_t) k[1])<<16);
break;
case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
case 6 : b+=k[2];
a+=k[0]+(((uint32_t) k[1])<<16);
break;
case 5 : b+=k8[4]; /* fall through */
case 4 : a+=k[0]+(((uint32_t) k[1])<<16);
break;
case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
case 2 : a+=k[0];
break;
case 1 : a+=k8[0];
break;
case 0 : return c; /* zero length requires no mixing */
}
} else { /* need to read the key one byte at a time */
const uint8_t *k = (const uint8_t *)key;
/*--------------- all but the last block: affect some 32 bits of (a, b, c) */
while (length > 12) {
a += k[0];
a += ((uint32_t) k[1])<<8;
a += ((uint32_t) k[2])<<16;
a += ((uint32_t) k[3])<<24;
b += k[4];
b += ((uint32_t) k[5])<<8;
b += ((uint32_t) k[6])<<16;
b += ((uint32_t) k[7])<<24;
c += k[8];
c += ((uint32_t) k[9])<<8;
c += ((uint32_t) k[10])<<16;
c += ((uint32_t) k[11])<<24;
mix(a,b,c);
length -= 12;
k += 12;
}
/*-------------------------------- last block: affect all 32 bits of (c) */
switch (length) { /* all the case statements fall through */
case 12: c+=((uint32_t) k[11])<<24;
case 11: c+=((uint32_t) k[10])<<16;
case 10: c+=((uint32_t) k[9])<<8;
case 9 : c+=k[8];
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];
break;
case 0 : return c;
}
}
final(a, b, c);
return c;
}
static inline
uint32_t jhash(const void *key, size_t length, uint32_t seed)
{
return hashlittle(key, length, seed);
}
#endif /* _JHASH_H */
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