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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 includedif SELF_TEST is defined. You can use this free for any purpose. It's inthe public domain. It has no warranty.
You probably want to use hashlittle(). hashlittle() and hashbig()hash byte arrays. hashlittle() is is faster than hashbig() onlittle-endian machines. Intel and AMD are little-endian machines.On second thought, you probably want hashlittle2(), which is identical tohashlittle() 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, doa = 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 of4-byte integers to hash, use hashword(). If you have a byte array (likea character string), use hashlittle(). If you have several byte arrays, ora 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 thoroughmixing with 12*3 instructions on 3 integers than you can with 3 instructionson 1 byte), but shoehorning those bytes into integers efficiently is messy.*/
#include "jhash.h"
/** My best guess at if you are big-endian or little-endian. This may* need adjustment.*/#if defined(ROCKBOX_LITTLE_ENDIAN)# define HASH_LITTLE_ENDIAN 1# define HASH_BIG_ENDIAN 0#elif defined(ROCKBOX_BIG_ENDIAN)# define HASH_LITTLE_ENDIAN 0# define HASH_BIG_ENDIAN 1#else# define HASH_LITTLE_ENDIAN 0# define HASH_BIG_ENDIAN 0#endif
#define hashsize(n) ((uint32_t)1<<(n))#define hashmask(n) (hashsize(n)-1)#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
/*
mix -- mix 3 32-bit values reversibly.
This is reversible, so any information in (a,b,c) before mix() isstill in (a,b,c) after mix().
If four pairs of (a,b,c) inputs are run through mix(), or throughmix() in reverse, there are at least 32 bits of the output thatare sometimes the same for one pair and different for another pair.This was tested for:* pairs that differed by one bit, by two bits, in any combination of top bits of (a,b,c), or in any combination of bottom bits of (a,b,c).* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed the output delta to a Gray code (a^(a>>1)) so a string of 1's (as is commonly produced by subtraction) look like a single 1-bit difference.* the base values were pseudorandom, all zero but one bit set, or all zero plus a counter that starts at zero.
Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement thatsatisfy this are 4 6 8 16 19 4 9 15 3 18 27 15 14 9 3 7 17 3Well, "9 15 3 18 27 15" didn't quite get 32 bits diffingfor "differ" defined as + with a one-bit base and a two-bit delta. Iused http://burtleburtle.net/bob/hash/avalanche.html to choosethe operations, constants, and arrangements of the variables.
This does not achieve avalanche. There are input bits of (a,b,c)that fail to affect some output bits of (a,b,c), especially of a. Themost thoroughly mixed value is c, but it doesn't really even achieveavalanche in c.
This allows some parallelism. Read-after-writes are good at doublingthe number of bits affected, so the goal of mixing pulls in the oppositedirection as the goal of parallelism. I did what I could. Rotatesseem to cost as much as shifts on every machine I could lay my handson, and rotates are much kinder to the top and bottom bits, so I usedrotates.*/#define mix(a,b,c) \{ \ 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; \}
/*final -- final mixing of 3 32-bit values (a,b,c) into c
Pairs of (a,b,c) values differing in only a few bits will usuallyproduce values of c that look totally different. This was tested for* pairs that differed by one bit, by two bits, in any combination of top bits of (a,b,c), or in any combination of bottom bits of(a,b,c).* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed the output delta to a Gray code (a^(a>>1)) so a string of 1's (as is commonly produced by subtraction) look like a single 1-bit difference.* the base values were pseudorandom, all zero but one bit set, or all zero plus a counter that starts at zero.
These constants passed: 14 11 25 16 4 14 24 12 14 25 16 4 14 24and these came close: 4 8 15 26 3 22 24 10 8 15 26 3 22 24 11 8 15 26 3 22 24*/#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); \}
/* k: pointer to the key, an array of uint32_t length: number of elements in the key initval: an initialization value returns the 32-bit hash*/uint32_t hashw(const uint32_t *k, size_t length, uint32_t initval){ uint32_t a, b, c;
/* Set up the internal state */ a = b = c = 0xdeadbeef + (((uint32_t)length)<<2) + initval;
/* handle most of the key */ while (length > 3) { a += k[0]; b += k[1]; c += k[2]; mix(a,b,c); length -= 3; k += 3; }
/* handle the last 3 uint32_t's */ switch(length) /* all the case statements fall through */ { case 3: c+=k[2]; case 2: b+=k[1]; case 1: a+=k[0]; final(a,b,c); case 0: /* case 0: nothing left to add */ break; } /* report the result */ return c;}
/*hashw2() -- same as hashw(), but take two seeds and return two32-bit values. pc and pb must both be nonnull, and *pc and *pb mustboth be initialized with seeds. If you pass in (*pb)==0, the output(*pc) will be the same as the return value from hashword(). k: pointer to the key, an array of uint32_t length: number of elements in the key pc, pb: pointers to primary and secondary initial values, also used to store the hash results.*/void hashw2 (const uint32_t *k, size_t length, uint32_t *pc, uint32_t *pb){ uint32_t a,b,c;
/* Set up the internal state */ a = b = c = 0xdeadbeef + ((uint32_t)(length<<2)) + *pc; c += *pb;
/* handle most of the key */ while (length > 3) { a += k[0]; b += k[1]; c += k[2]; mix(a,b,c); length -= 3; k += 3; }
/* handle the last 3 uint32_t's */ switch(length) /* all the case statements fall through */ { case 3: c+=k[2]; case 2: b+=k[1]; case 1: a+=k[0]; final(a,b,c); case 0: /* case 0: nothing left to add */ break; } /* report the result */ *pc=c; *pb=b;}
/*hashs() -- hash a variable-length key into a 32-bit value k: pointer to the key, an array of bytes length: number of elements in the key initval: an initialization value returns the 32-bit hashReturns a 32-bit value. Every bit of the key affects every bit ofthe return value. Two keys differing by one or two bits will havetotally different hash values.
The best hash table sizes are powers of 2. There is no need to domod a prime (mod is sooo slow!). If you need less than 32 bits,use a bitmask. For example, if you need only 10 bits, doh = (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 thiscode any way you wish, private, educational, or commercial. It's free.
Use for hash table lookup, or anything where one collision in 2^^32 isacceptable. Do NOT use for cryptographic purposes.*/
uint32_t hashs( const void *key, size_t length, uint32_t initval){ uint32_t a,b,c; /* internal state */#if HASH_LITTLE_ENDIAN union { const void *ptr; size_t i; } u;/* needed for Mac Powerbook G4 */#endif
/* Set up the internal state */ a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
#if HASH_LITTLE_ENDIAN u.ptr = key; if ((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 */ 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 if ((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#endif { /* 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;}
/*hashs2: return 2 32-bit hash values k: pointer to the key, an array of bytes length: number of elements in the key pc, pb: pointers to primary and secondary initial values, also used to store the hash results.* 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 hashs2(const void *key, size_t length, uint32_t *pc, uint32_t *pb){ uint32_t a, b, c; /* internal state */#if HASH_LITTLE_ENDIAN union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */#endif
/* Set up the internal state */ a = b = c = 0xdeadbeef + ((uint32_t)length) + *pc; c += *pb;
#if HASH_LITTLE_ENDIAN u.ptr = key; if (((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 */ 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: *pc=c; *pb=b; return; /* zero length strings require no mixing */ } } else if (((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: *pc=c; *pb=b; return; /* zero length strings require no mixing */ } } else#endif { /* 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: *pc=c; *pb=b; return; /* zero length strings require no mixing */ } }
final(a,b,c); *pc=c; *pb=b;}