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+/*
+--------------------------------------------------------------------
+lookupa.c, by Bob Jenkins, December 1996. Same as lookup2.c
+Use this code however you wish. Public Domain. No warranty.
+Source is http://burtleburtle.net/bob/c/lookupa.c
+--------------------------------------------------------------------
+*/
+#ifndef LOOKUPA
+#include "lookupa.h"
+#endif
+
+/*
+--------------------------------------------------------------------
+mix -- mix 3 32-bit values reversibly.
+For every delta with one or two bit set, and the deltas of all three
+ high bits or all three low bits, whether the original value of a,b,c
+ is almost all zero or is uniformly distributed,
+* If mix() is run forward or backward, at least 32 bits in a,b,c
+ have at least 1/4 probability of changing.
+* If mix() is run forward, every bit of c will change between 1/3 and
+ 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
+mix() was built out of 36 single-cycle latency instructions in a
+ structure that could supported 2x parallelism, like so:
+ a -= b;
+ a -= c; x = (c>>13);
+ b -= c; a ^= x;
+ b -= a; x = (a<<8);
+ c -= a; b ^= x;
+ c -= b; x = (b>>13);
+ ...
+ Unfortunately, superscalar Pentiums and Sparcs can't take advantage
+ of that parallelism. They've also turned some of those single-cycle
+ latency instructions into multi-cycle latency instructions. Still,
+ this is the fastest good hash I could find. There were about 2^^68
+ to choose from. I only looked at a billion or so.
+--------------------------------------------------------------------
+*/
+#define mix(a,b,c) \
+{ \
+ a -= b; a -= c; a ^= (c>>13); \
+ b -= c; b -= a; b ^= (a<<8); \
+ c -= a; c -= b; c ^= (b>>13); \
+ a -= b; a -= c; a ^= (c>>12); \
+ b -= c; b -= a; b ^= (a<<16); \
+ c -= a; c -= b; c ^= (b>>5); \
+ a -= b; a -= c; a ^= (c>>3); \
+ b -= c; b -= a; b ^= (a<<10); \
+ c -= a; c -= b; c ^= (b>>15); \
+}
+
+/*
+--------------------------------------------------------------------
+lookup() -- hash a variable-length key into a 32-bit value
+ k : the key (the unaligned variable-length array of bytes)
+ len : the length of the key, counting by bytes
+ level : can be any 4-byte value
+Returns a 32-bit value. Every bit of the key affects every bit of
+the return value. Every 1-bit and 2-bit delta achieves avalanche.
+About 6len+35 instructions.
+
+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 (ub1 **)k, do it like this:
+ for (i=0, h=0; i<n; ++i) h = lookup( k[i], len[i], h);
+
+By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
+code any way you wish, private, educational, or commercial.
+
+See http://burtleburtle.net/bob/hash/evahash.html
+Use for hash table lookup, or anything where one collision in 2^32 is
+acceptable. Do NOT use for cryptographic purposes.
+--------------------------------------------------------------------
+*/
+
+Uint32 lookup( k, length, level)
+register Uint8 *k; /* the key */
+register Uint32 length; /* the length of the key */
+register Uint32 level; /* the previous hash, or an arbitrary value */
+{
+ register Uint32 a,b,c,len;
+
+ /* Set up the internal state */
+ len = length;
+ a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
+ c = level; /* the previous hash value */
+
+ /*---------------------------------------- handle most of the key */
+ while (len >= 12)
+ {
+ a += (k[0] +((Uint32)k[1]<<8) +((Uint32)k[2]<<16) +((Uint32)k[3]<<24));
+ b += (k[4] +((Uint32)k[5]<<8) +((Uint32)k[6]<<16) +((Uint32)k[7]<<24));
+ c += (k[8] +((Uint32)k[9]<<8) +((Uint32)k[10]<<16)+((Uint32)k[11]<<24));
+ mix(a,b,c);
+ k += 12; len -= 12;
+ }
+
+ /*------------------------------------- handle the last 11 bytes */
+ c += length;
+ switch(len) /* all the case statements fall through */
+ {
+ case 11: c+=((Uint32)k[10]<<24);
+ case 10: c+=((Uint32)k[9]<<16);
+ case 9 : c+=((Uint32)k[8]<<8);
+ /* the first byte of c is reserved for the length */
+ case 8 : b+=((Uint32)k[7]<<24);
+ case 7 : b+=((Uint32)k[6]<<16);
+ case 6 : b+=((Uint32)k[5]<<8);
+ case 5 : b+=k[4];
+ case 4 : a+=((Uint32)k[3]<<24);
+ case 3 : a+=((Uint32)k[2]<<16);
+ case 2 : a+=((Uint32)k[1]<<8);
+ case 1 : a+=k[0];
+ /* case 0: nothing left to add */
+ }
+ mix(a,b,c);
+ /*-------------------------------------------- report the result */
+ return c;
+}
+
+
+/*
+--------------------------------------------------------------------
+mixc -- mixc 8 4-bit values as quickly and thoroughly as possible.
+Repeating mix() three times achieves avalanche.
+Repeating mix() four times eliminates all funnels and all
+ characteristics stronger than 2^{-11}.
+--------------------------------------------------------------------
+*/
+#define mixc(a,b,c,d,e,f,g,h) \
+{ \
+ a^=b<<11; d+=a; b+=c; \
+ b^=c>>2; e+=b; c+=d; \
+ c^=d<<8; f+=c; d+=e; \
+ d^=e>>16; g+=d; e+=f; \
+ e^=f<<10; h+=e; f+=g; \
+ f^=g>>4; a+=f; g+=h; \
+ g^=h<<8; b+=g; h+=a; \
+ h^=a>>9; c+=h; a+=b; \
+}
+
+/*
+--------------------------------------------------------------------
+checksum() -- hash a variable-length key into a 256-bit value
+ k : the key (the unaligned variable-length array of bytes)
+ len : the length of the key, counting by bytes
+ state : an array of CHECKSTATE 4-byte values (256 bits)
+The state is the checksum. Every bit of the key affects every bit of
+the state. There are no funnels. About 112+6.875len instructions.
+
+If you are hashing n strings (ub1 **)k, do it like this:
+ for (i=0; i<8; ++i) state[i] = 0x9e3779b9;
+ for (i=0, h=0; i<n; ++i) checksum( k[i], len[i], state);
+
+(c) Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
+code any way you wish, private, educational, or commercial, as long
+as this whole comment accompanies it.
+
+See http://burtleburtle.net/bob/hash/evahash.html
+Use to detect changes between revisions of documents, assuming nobody
+is trying to cause collisions. Do NOT use for cryptography.
+--------------------------------------------------------------------
+*/
+void checksum( k, len, state)
+register Uint8 *k;
+register Uint32 len;
+register Uint32*state;
+{
+ register Uint32 a,b,c,d,e,f,g,h,length;
+
+ /* Use the length and level; add in the golden ratio. */
+ length = len;
+ a=state[0]; b=state[1]; c=state[2]; d=state[3];
+ e=state[4]; f=state[5]; g=state[6]; h=state[7];
+
+ /*---------------------------------------- handle most of the key */
+ while (len >= 32)
+ {
+ a += (k[0] +(k[1]<<8) +(k[2]<<16) +(k[3]<<24));
+ b += (k[4] +(k[5]<<8) +(k[6]<<16) +(k[7]<<24));
+ c += (k[8] +(k[9]<<8) +(k[10]<<16)+(k[11]<<24));
+ d += (k[12]+(k[13]<<8)+(k[14]<<16)+(k[15]<<24));
+ e += (k[16]+(k[17]<<8)+(k[18]<<16)+(k[19]<<24));
+ f += (k[20]+(k[21]<<8)+(k[22]<<16)+(k[23]<<24));
+ g += (k[24]+(k[25]<<8)+(k[26]<<16)+(k[27]<<24));
+ h += (k[28]+(k[29]<<8)+(k[30]<<16)+(k[31]<<24));
+ mixc(a,b,c,d,e,f,g,h);
+ mixc(a,b,c,d,e,f,g,h);
+ mixc(a,b,c,d,e,f,g,h);
+ mixc(a,b,c,d,e,f,g,h);
+ k += 32; len -= 32;
+ }
+
+ /*------------------------------------- handle the last 31 bytes */
+ h += length;
+ switch(len)
+ {
+ case 31: h+=(k[30]<<24);
+ case 30: h+=(k[29]<<16);
+ case 29: h+=(k[28]<<8);
+ case 28: g+=(k[27]<<24);
+ case 27: g+=(k[26]<<16);
+ case 26: g+=(k[25]<<8);
+ case 25: g+=k[24];
+ case 24: f+=(k[23]<<24);
+ case 23: f+=(k[22]<<16);
+ case 22: f+=(k[21]<<8);
+ case 21: f+=k[20];
+ case 20: e+=(k[19]<<24);
+ case 19: e+=(k[18]<<16);
+ case 18: e+=(k[17]<<8);
+ case 17: e+=k[16];
+ case 16: d+=(k[15]<<24);
+ case 15: d+=(k[14]<<16);
+ case 14: d+=(k[13]<<8);
+ case 13: d+=k[12];
+ case 12: c+=(k[11]<<24);
+ case 11: c+=(k[10]<<16);
+ case 10: c+=(k[9]<<8);
+ case 9 : c+=k[8];
+ case 8 : b+=(k[7]<<24);
+ case 7 : b+=(k[6]<<16);
+ case 6 : b+=(k[5]<<8);
+ case 5 : b+=k[4];
+ case 4 : a+=(k[3]<<24);
+ case 3 : a+=(k[2]<<16);
+ case 2 : a+=(k[1]<<8);
+ case 1 : a+=k[0];
+ }
+ mixc(a,b,c,d,e,f,g,h);
+ mixc(a,b,c,d,e,f,g,h);
+ mixc(a,b,c,d,e,f,g,h);
+ mixc(a,b,c,d,e,f,g,h);
+
+ /*-------------------------------------------- report the result */
+ state[0]=a; state[1]=b; state[2]=c; state[3]=d;
+ state[4]=e; state[5]=f; state[6]=g; state[7]=h;
+}
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