Annotation of embedaddon/trafshow/lookupa.c, revision 1.1
1.1 ! misho 1: /*
! 2: --------------------------------------------------------------------
! 3: lookupa.c, by Bob Jenkins, December 1996. Same as lookup2.c
! 4: Use this code however you wish. Public Domain. No warranty.
! 5: Source is http://burtleburtle.net/bob/c/lookupa.c
! 6: --------------------------------------------------------------------
! 7: */
! 8: #ifndef STANDARD
! 9: #include "standard.h"
! 10: #endif
! 11: #ifndef LOOKUPA
! 12: #include "lookupa.h"
! 13: #endif
! 14:
! 15: /*
! 16: --------------------------------------------------------------------
! 17: mix -- mix 3 32-bit values reversibly.
! 18: For every delta with one or two bit set, and the deltas of all three
! 19: high bits or all three low bits, whether the original value of a,b,c
! 20: is almost all zero or is uniformly distributed,
! 21: * If mix() is run forward or backward, at least 32 bits in a,b,c
! 22: have at least 1/4 probability of changing.
! 23: * If mix() is run forward, every bit of c will change between 1/3 and
! 24: 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
! 25: mix() was built out of 36 single-cycle latency instructions in a
! 26: structure that could supported 2x parallelism, like so:
! 27: a -= b;
! 28: a -= c; x = (c>>13);
! 29: b -= c; a ^= x;
! 30: b -= a; x = (a<<8);
! 31: c -= a; b ^= x;
! 32: c -= b; x = (b>>13);
! 33: ...
! 34: Unfortunately, superscalar Pentiums and Sparcs can't take advantage
! 35: of that parallelism. They've also turned some of those single-cycle
! 36: latency instructions into multi-cycle latency instructions. Still,
! 37: this is the fastest good hash I could find. There were about 2^^68
! 38: to choose from. I only looked at a billion or so.
! 39: --------------------------------------------------------------------
! 40: */
! 41: #define mix(a,b,c) \
! 42: { \
! 43: a -= b; a -= c; a ^= (c>>13); \
! 44: b -= c; b -= a; b ^= (a<<8); \
! 45: c -= a; c -= b; c ^= (b>>13); \
! 46: a -= b; a -= c; a ^= (c>>12); \
! 47: b -= c; b -= a; b ^= (a<<16); \
! 48: c -= a; c -= b; c ^= (b>>5); \
! 49: a -= b; a -= c; a ^= (c>>3); \
! 50: b -= c; b -= a; b ^= (a<<10); \
! 51: c -= a; c -= b; c ^= (b>>15); \
! 52: }
! 53:
! 54: /*
! 55: --------------------------------------------------------------------
! 56: lookup() -- hash a variable-length key into a 32-bit value
! 57: k : the key (the unaligned variable-length array of bytes)
! 58: len : the length of the key, counting by bytes
! 59: level : can be any 4-byte value
! 60: Returns a 32-bit value. Every bit of the key affects every bit of
! 61: the return value. Every 1-bit and 2-bit delta achieves avalanche.
! 62: About 6len+35 instructions.
! 63:
! 64: The best hash table sizes are powers of 2. There is no need to do
! 65: mod a prime (mod is sooo slow!). If you need less than 32 bits,
! 66: use a bitmask. For example, if you need only 10 bits, do
! 67: h = (h & hashmask(10));
! 68: In which case, the hash table should have hashsize(10) elements.
! 69:
! 70: If you are hashing n strings (ub1 **)k, do it like this:
! 71: for (i=0, h=0; i<n; ++i) h = lookup( k[i], len[i], h);
! 72:
! 73: By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
! 74: code any way you wish, private, educational, or commercial.
! 75:
! 76: See http://burtleburtle.net/bob/hash/evahash.html
! 77: Use for hash table lookup, or anything where one collision in 2^32 is
! 78: acceptable. Do NOT use for cryptographic purposes.
! 79: --------------------------------------------------------------------
! 80: */
! 81:
! 82: ub4 lookup( k, length, level)
! 83: register ub1 *k; /* the key */
! 84: register ub4 length; /* the length of the key */
! 85: register ub4 level; /* the previous hash, or an arbitrary value */
! 86: {
! 87: register ub4 a,b,c,len;
! 88:
! 89: /* Set up the internal state */
! 90: len = length;
! 91: a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
! 92: c = level; /* the previous hash value */
! 93:
! 94: /*---------------------------------------- handle most of the key */
! 95: while (len >= 12)
! 96: {
! 97: a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
! 98: b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
! 99: c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
! 100: mix(a,b,c);
! 101: k += 12; len -= 12;
! 102: }
! 103:
! 104: /*------------------------------------- handle the last 11 bytes */
! 105: c += length;
! 106: switch(len) /* all the case statements fall through */
! 107: {
! 108: case 11: c+=((ub4)k[10]<<24);
! 109: case 10: c+=((ub4)k[9]<<16);
! 110: case 9 : c+=((ub4)k[8]<<8);
! 111: /* the first byte of c is reserved for the length */
! 112: case 8 : b+=((ub4)k[7]<<24);
! 113: case 7 : b+=((ub4)k[6]<<16);
! 114: case 6 : b+=((ub4)k[5]<<8);
! 115: case 5 : b+=k[4];
! 116: case 4 : a+=((ub4)k[3]<<24);
! 117: case 3 : a+=((ub4)k[2]<<16);
! 118: case 2 : a+=((ub4)k[1]<<8);
! 119: case 1 : a+=k[0];
! 120: /* case 0: nothing left to add */
! 121: }
! 122: mix(a,b,c);
! 123: /*-------------------------------------------- report the result */
! 124: return c;
! 125: }
! 126:
! 127:
! 128: /*
! 129: --------------------------------------------------------------------
! 130: mixc -- mixc 8 4-bit values as quickly and thoroughly as possible.
! 131: Repeating mix() three times achieves avalanche.
! 132: Repeating mix() four times eliminates all funnels and all
! 133: characteristics stronger than 2^{-11}.
! 134: --------------------------------------------------------------------
! 135: */
! 136: #define mixc(a,b,c,d,e,f,g,h) \
! 137: { \
! 138: a^=b<<11; d+=a; b+=c; \
! 139: b^=c>>2; e+=b; c+=d; \
! 140: c^=d<<8; f+=c; d+=e; \
! 141: d^=e>>16; g+=d; e+=f; \
! 142: e^=f<<10; h+=e; f+=g; \
! 143: f^=g>>4; a+=f; g+=h; \
! 144: g^=h<<8; b+=g; h+=a; \
! 145: h^=a>>9; c+=h; a+=b; \
! 146: }
! 147:
! 148: /*
! 149: --------------------------------------------------------------------
! 150: checksum() -- hash a variable-length key into a 256-bit value
! 151: k : the key (the unaligned variable-length array of bytes)
! 152: len : the length of the key, counting by bytes
! 153: state : an array of CHECKSTATE 4-byte values (256 bits)
! 154: The state is the checksum. Every bit of the key affects every bit of
! 155: the state. There are no funnels. About 112+6.875len instructions.
! 156:
! 157: If you are hashing n strings (ub1 **)k, do it like this:
! 158: for (i=0; i<8; ++i) state[i] = 0x9e3779b9;
! 159: for (i=0, h=0; i<n; ++i) checksum( k[i], len[i], state);
! 160:
! 161: (c) Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
! 162: code any way you wish, private, educational, or commercial, as long
! 163: as this whole comment accompanies it.
! 164:
! 165: See http://burtleburtle.net/bob/hash/evahash.html
! 166: Use to detect changes between revisions of documents, assuming nobody
! 167: is trying to cause collisions. Do NOT use for cryptography.
! 168: --------------------------------------------------------------------
! 169: */
! 170: void checksum( k, len, state)
! 171: register ub1 *k;
! 172: register ub4 len;
! 173: register ub4 *state;
! 174: {
! 175: register ub4 a,b,c,d,e,f,g,h,length;
! 176:
! 177: /* Use the length and level; add in the golden ratio. */
! 178: length = len;
! 179: a=state[0]; b=state[1]; c=state[2]; d=state[3];
! 180: e=state[4]; f=state[5]; g=state[6]; h=state[7];
! 181:
! 182: /*---------------------------------------- handle most of the key */
! 183: while (len >= 32)
! 184: {
! 185: a += (k[0] +(k[1]<<8) +(k[2]<<16) +(k[3]<<24));
! 186: b += (k[4] +(k[5]<<8) +(k[6]<<16) +(k[7]<<24));
! 187: c += (k[8] +(k[9]<<8) +(k[10]<<16)+(k[11]<<24));
! 188: d += (k[12]+(k[13]<<8)+(k[14]<<16)+(k[15]<<24));
! 189: e += (k[16]+(k[17]<<8)+(k[18]<<16)+(k[19]<<24));
! 190: f += (k[20]+(k[21]<<8)+(k[22]<<16)+(k[23]<<24));
! 191: g += (k[24]+(k[25]<<8)+(k[26]<<16)+(k[27]<<24));
! 192: h += (k[28]+(k[29]<<8)+(k[30]<<16)+(k[31]<<24));
! 193: mixc(a,b,c,d,e,f,g,h);
! 194: mixc(a,b,c,d,e,f,g,h);
! 195: mixc(a,b,c,d,e,f,g,h);
! 196: mixc(a,b,c,d,e,f,g,h);
! 197: k += 32; len -= 32;
! 198: }
! 199:
! 200: /*------------------------------------- handle the last 31 bytes */
! 201: h += length;
! 202: switch(len)
! 203: {
! 204: case 31: h+=(k[30]<<24);
! 205: case 30: h+=(k[29]<<16);
! 206: case 29: h+=(k[28]<<8);
! 207: case 28: g+=(k[27]<<24);
! 208: case 27: g+=(k[26]<<16);
! 209: case 26: g+=(k[25]<<8);
! 210: case 25: g+=k[24];
! 211: case 24: f+=(k[23]<<24);
! 212: case 23: f+=(k[22]<<16);
! 213: case 22: f+=(k[21]<<8);
! 214: case 21: f+=k[20];
! 215: case 20: e+=(k[19]<<24);
! 216: case 19: e+=(k[18]<<16);
! 217: case 18: e+=(k[17]<<8);
! 218: case 17: e+=k[16];
! 219: case 16: d+=(k[15]<<24);
! 220: case 15: d+=(k[14]<<16);
! 221: case 14: d+=(k[13]<<8);
! 222: case 13: d+=k[12];
! 223: case 12: c+=(k[11]<<24);
! 224: case 11: c+=(k[10]<<16);
! 225: case 10: c+=(k[9]<<8);
! 226: case 9 : c+=k[8];
! 227: case 8 : b+=(k[7]<<24);
! 228: case 7 : b+=(k[6]<<16);
! 229: case 6 : b+=(k[5]<<8);
! 230: case 5 : b+=k[4];
! 231: case 4 : a+=(k[3]<<24);
! 232: case 3 : a+=(k[2]<<16);
! 233: case 2 : a+=(k[1]<<8);
! 234: case 1 : a+=k[0];
! 235: }
! 236: mixc(a,b,c,d,e,f,g,h);
! 237: mixc(a,b,c,d,e,f,g,h);
! 238: mixc(a,b,c,d,e,f,g,h);
! 239: mixc(a,b,c,d,e,f,g,h);
! 240:
! 241: /*-------------------------------------------- report the result */
! 242: state[0]=a; state[1]=b; state[2]=c; state[3]=d;
! 243: state[4]=e; state[5]=f; state[6]=g; state[7]=h;
! 244: }
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>
![[BACK]](/icons/cvsweb/back.gif){kind=icon}
Return to lookupa.c CVS log ![[TXT]](/icons/cvsweb/text.gif){kind=icon}
![[DIR]](/icons/cvsweb/dir.gif){kind=icon}
Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / trafshow