264 lines
9 KiB
C
264 lines
9 KiB
C
/*
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* This file is a part of Pcompress, a chunked parallel multi-
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* algorithm lossless compression and decompression program.
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*
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* Copyright (C) 2012-2013 Moinak Ghosh. All rights reserved.
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* Use is subject to license terms.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 3 of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this program.
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* If not, see <http://www.gnu.org/licenses/>.
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*
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* moinakg@belenix.org, http://moinakg.wordpress.com/
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*
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*/
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/*
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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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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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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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/* k: the key */
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/* length: the length of the key */
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/* level: the previous hash, or an arbitrary value */
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ub4
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lookup(ub1 *k, ub4 length, ub4 level)
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{
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register ub4 a,b,c,len;
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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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/*---------------------------------------- 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
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checksum(ub1 *k, ub4 len, 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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/* 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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