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240 lines
8.1 KiB
240 lines
8.1 KiB
/* |
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-------------------------------------------------------------------- |
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lookupa.c, by Bob Jenkins, December 1996. Same as lookup2.c |
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Use this code however you wish. Public Domain. No warranty. |
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Source is http://burtleburtle.net/bob/c/lookupa.c |
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-------------------------------------------------------------------- |
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*/ |
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#ifndef STANDARD |
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#include "standard.h" |
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#endif |
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#ifndef LOOKUPA |
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#include "lookupa.h" |
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#endif |
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/* |
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-------------------------------------------------------------------- |
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mix -- mix 3 32-bit values reversibly. |
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For every delta with one or two bit set, and the deltas of all three |
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high bits or all three low bits, whether the original value of a,b,c |
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is almost all zero or is uniformly distributed, |
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* If mix() is run forward or backward, at least 32 bits in a,b,c |
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have at least 1/4 probability of changing. |
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* If mix() is run forward, every bit of c will change between 1/3 and |
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2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.) |
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mix() was built out of 36 single-cycle latency instructions in a |
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structure that could supported 2x parallelism, like so: |
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a -= b; |
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a -= c; x = (c>>13); |
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b -= c; a ^= x; |
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b -= a; x = (a<<8); |
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c -= a; b ^= x; |
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c -= b; x = (b>>13); |
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... |
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Unfortunately, superscalar Pentiums and Sparcs can't take advantage |
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of that parallelism. They've also turned some of those single-cycle |
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latency instructions into multi-cycle latency instructions. Still, |
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this is the fastest good hash I could find. There were about 2^^68 |
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to choose from. I only looked at a billion or so. |
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-------------------------------------------------------------------- |
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*/ |
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#define mix(a,b,c) \ |
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{ \ |
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a -= b; a -= c; a ^= (c>>13); \ |
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b -= c; b -= a; b ^= (a<<8); \ |
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c -= a; c -= b; c ^= (b>>13); \ |
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a -= b; a -= c; a ^= (c>>12); \ |
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b -= c; b -= a; b ^= (a<<16); \ |
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c -= a; c -= b; c ^= (b>>5); \ |
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a -= b; a -= c; a ^= (c>>3); \ |
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b -= c; b -= a; b ^= (a<<10); \ |
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c -= a; c -= b; c ^= (b>>15); \ |
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} |
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/* |
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-------------------------------------------------------------------- |
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lookup() -- hash a variable-length key into a 32-bit value |
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k : the key (the unaligned variable-length array of bytes) |
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len : the length of the key, counting by bytes |
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level : can be any 4-byte value |
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Returns a 32-bit value. Every bit of the key affects every bit of |
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the return value. Every 1-bit and 2-bit delta achieves avalanche. |
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About 6len+35 instructions. |
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|
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The best hash table sizes are powers of 2. There is no need to do |
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mod a prime (mod is sooo slow!). If you need less than 32 bits, |
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use a bitmask. For example, if you need only 10 bits, do |
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h = (h & hashmask(10)); |
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In which case, the hash table should have hashsize(10) elements. |
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|
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If you are hashing n strings (ub1 **)k, do it like this: |
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for (i=0, h=0; i<n; ++i) h = lookup( k[i], len[i], h); |
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By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this |
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code any way you wish, private, educational, or commercial. |
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See http://burtleburtle.net/bob/hash/evahash.html |
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Use for hash table lookup, or anything where one collision in 2^32 is |
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acceptable. Do NOT use for cryptographic purposes. |
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-------------------------------------------------------------------- |
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*/ |
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ub4 lookup( k, length, level) |
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register ub1 *k; /* the key */ |
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register ub4 length; /* the length of the key */ |
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register ub4 level; /* the previous hash, or an arbitrary value */ |
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{ |
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register ub4 a,b,c,len; |
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|
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/* Set up the internal state */ |
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len = length; |
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a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */ |
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c = level; /* the previous hash value */ |
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|
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/*---------------------------------------- handle most of the key */ |
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while (len >= 12) |
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{ |
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a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24)); |
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b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24)); |
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c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24)); |
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mix(a,b,c); |
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k += 12; len -= 12; |
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} |
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/*------------------------------------- handle the last 11 bytes */ |
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c += length; |
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switch(len) /* all the case statements fall through */ |
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{ |
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case 11: c+=((ub4)k[10]<<24); |
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case 10: c+=((ub4)k[9]<<16); |
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case 9 : c+=((ub4)k[8]<<8); |
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/* the first byte of c is reserved for the length */ |
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case 8 : b+=((ub4)k[7]<<24); |
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case 7 : b+=((ub4)k[6]<<16); |
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case 6 : b+=((ub4)k[5]<<8); |
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case 5 : b+=k[4]; |
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case 4 : a+=((ub4)k[3]<<24); |
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case 3 : a+=((ub4)k[2]<<16); |
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case 2 : a+=((ub4)k[1]<<8); |
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case 1 : a+=k[0]; |
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/* case 0: nothing left to add */ |
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} |
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mix(a,b,c); |
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/*-------------------------------------------- report the result */ |
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return c; |
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} |
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/* |
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-------------------------------------------------------------------- |
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mixc -- mixc 8 4-bit values as quickly and thoroughly as possible. |
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Repeating mix() three times achieves avalanche. |
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Repeating mix() four times eliminates all funnels and all |
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characteristics stronger than 2^{-11}. |
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-------------------------------------------------------------------- |
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*/ |
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#define mixc(a,b,c,d,e,f,g,h) \ |
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{ \ |
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a^=b<<11; d+=a; b+=c; \ |
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b^=c>>2; e+=b; c+=d; \ |
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c^=d<<8; f+=c; d+=e; \ |
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d^=e>>16; g+=d; e+=f; \ |
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e^=f<<10; h+=e; f+=g; \ |
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f^=g>>4; a+=f; g+=h; \ |
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g^=h<<8; b+=g; h+=a; \ |
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h^=a>>9; c+=h; a+=b; \ |
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} |
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/* |
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-------------------------------------------------------------------- |
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checksum() -- hash a variable-length key into a 256-bit value |
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k : the key (the unaligned variable-length array of bytes) |
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len : the length of the key, counting by bytes |
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state : an array of CHECKSTATE 4-byte values (256 bits) |
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The state is the checksum. Every bit of the key affects every bit of |
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the state. There are no funnels. About 112+6.875len instructions. |
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If you are hashing n strings (ub1 **)k, do it like this: |
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for (i=0; i<8; ++i) state[i] = 0x9e3779b9; |
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for (i=0, h=0; i<n; ++i) checksum( k[i], len[i], state); |
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See http://burtleburtle.net/bob/hash/evahash.html |
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Use to detect changes between revisions of documents, assuming nobody |
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is trying to cause collisions. Do NOT use for cryptography. |
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-------------------------------------------------------------------- |
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*/ |
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void checksum( k, len, state) |
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register ub1 *k; |
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register ub4 len; |
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register ub4 *state; |
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{ |
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register ub4 a,b,c,d,e,f,g,h,length; |
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|
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/* Use the length and level; add in the golden ratio. */ |
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length = len; |
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a=state[0]; b=state[1]; c=state[2]; d=state[3]; |
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e=state[4]; f=state[5]; g=state[6]; h=state[7]; |
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/*---------------------------------------- handle most of the key */ |
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while (len >= 32) |
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{ |
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a += (k[0] +(k[1]<<8) +(k[2]<<16) +(k[3]<<24)); |
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b += (k[4] +(k[5]<<8) +(k[6]<<16) +(k[7]<<24)); |
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c += (k[8] +(k[9]<<8) +(k[10]<<16)+(k[11]<<24)); |
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d += (k[12]+(k[13]<<8)+(k[14]<<16)+(k[15]<<24)); |
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e += (k[16]+(k[17]<<8)+(k[18]<<16)+(k[19]<<24)); |
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f += (k[20]+(k[21]<<8)+(k[22]<<16)+(k[23]<<24)); |
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g += (k[24]+(k[25]<<8)+(k[26]<<16)+(k[27]<<24)); |
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h += (k[28]+(k[29]<<8)+(k[30]<<16)+(k[31]<<24)); |
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mixc(a,b,c,d,e,f,g,h); |
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mixc(a,b,c,d,e,f,g,h); |
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mixc(a,b,c,d,e,f,g,h); |
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mixc(a,b,c,d,e,f,g,h); |
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k += 32; len -= 32; |
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} |
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/*------------------------------------- handle the last 31 bytes */ |
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h += length; |
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switch(len) |
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{ |
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case 31: h+=(k[30]<<24); |
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case 30: h+=(k[29]<<16); |
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case 29: h+=(k[28]<<8); |
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case 28: g+=(k[27]<<24); |
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case 27: g+=(k[26]<<16); |
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case 26: g+=(k[25]<<8); |
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case 25: g+=k[24]; |
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case 24: f+=(k[23]<<24); |
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case 23: f+=(k[22]<<16); |
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case 22: f+=(k[21]<<8); |
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case 21: f+=k[20]; |
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case 20: e+=(k[19]<<24); |
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case 19: e+=(k[18]<<16); |
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case 18: e+=(k[17]<<8); |
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case 17: e+=k[16]; |
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case 16: d+=(k[15]<<24); |
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case 15: d+=(k[14]<<16); |
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case 14: d+=(k[13]<<8); |
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case 13: d+=k[12]; |
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case 12: c+=(k[11]<<24); |
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case 11: c+=(k[10]<<16); |
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case 10: c+=(k[9]<<8); |
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case 9 : c+=k[8]; |
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case 8 : b+=(k[7]<<24); |
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case 7 : b+=(k[6]<<16); |
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case 6 : b+=(k[5]<<8); |
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case 5 : b+=k[4]; |
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case 4 : a+=(k[3]<<24); |
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case 3 : a+=(k[2]<<16); |
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case 2 : a+=(k[1]<<8); |
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case 1 : a+=k[0]; |
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} |
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mixc(a,b,c,d,e,f,g,h); |
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mixc(a,b,c,d,e,f,g,h); |
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mixc(a,b,c,d,e,f,g,h); |
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mixc(a,b,c,d,e,f,g,h); |
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/*-------------------------------------------- report the result */ |
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state[0]=a; state[1]=b; state[2]=c; state[3]=d; |
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state[4]=e; state[5]=f; state[6]=g; state[7]=h; |
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}
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