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Diffstat (limited to 'ext/mwrap/jhash.h')
| -rw-r--r-- | ext/mwrap/jhash.h | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/ext/mwrap/jhash.h b/ext/mwrap/jhash.h new file mode 100644 index 0000000..69666f3 --- /dev/null +++ b/ext/mwrap/jhash.h @@ -0,0 +1,256 @@ +#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 */ |