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Unix SMB/CIFS implementation.
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trivial database library
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Copyright (C) Rusty Russell 2010
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** NOTE! The following LGPL license applies to the tdb
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** library. This does NOT imply that all of Samba is released
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This library 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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This library 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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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, see <http://www.gnu.org/licenses/>.
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#include "tdb_private.h"
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/* This is based on the hash algorithm from gdbm */
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unsigned int tdb_old_hash(TDB_DATA *key)
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uint32_t value; /* Used to compute the hash value. */
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uint32_t i; /* Used to cycle through random values. */
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/* Set the initial value from the key size. */
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for (value = 0x238F13AF * key->dsize, i=0; i < key->dsize; i++)
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value = (value + (key->dptr[i] << (i*5 % 24)));
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return (1103515243 * value + 12345);
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#ifndef WORDS_BIGENDIAN
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# define HASH_LITTLE_ENDIAN 1
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# define HASH_BIG_ENDIAN 0
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# define HASH_LITTLE_ENDIAN 0
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# define HASH_BIG_ENDIAN 1
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-------------------------------------------------------------------------------
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lookup3.c, by Bob Jenkins, May 2006, Public Domain.
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These are functions for producing 32-bit hashes for hash table lookup.
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hash_word(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
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are externally useful functions. Routines to test the hash are included
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if SELF_TEST is defined. You can use this free for any purpose. It's in
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the public domain. It has no warranty.
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You probably want to use hashlittle(). hashlittle() and hashbig()
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hash byte arrays. hashlittle() is is faster than hashbig() on
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little-endian machines. Intel and AMD are little-endian machines.
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On second thought, you probably want hashlittle2(), which is identical to
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hashlittle() except it returns two 32-bit hashes for the price of one.
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You could implement hashbig2() if you wanted but I haven't bothered here.
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If you want to find a hash of, say, exactly 7 integers, do
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a = i1; b = i2; c = i3;
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a += i4; b += i5; c += i6;
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then use c as the hash value. If you have a variable length array of
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4-byte integers to hash, use hash_word(). If you have a byte array (like
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a character string), use hashlittle(). If you have several byte arrays, or
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a mix of things, see the comments above hashlittle().
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Why is this so big? I read 12 bytes at a time into 3 4-byte integers,
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then mix those integers. This is fast (you can do a lot more thorough
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mixing with 12*3 instructions on 3 integers than you can with 3 instructions
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on 1 byte), but shoehorning those bytes into integers efficiently is messy.
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#define hashsize(n) ((uint32_t)1<<(n))
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#define hashmask(n) (hashsize(n)-1)
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#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
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-------------------------------------------------------------------------------
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mix -- mix 3 32-bit values reversibly.
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This is reversible, so any information in (a,b,c) before mix() is
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still in (a,b,c) after mix().
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If four pairs of (a,b,c) inputs are run through mix(), or through
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mix() in reverse, there are at least 32 bits of the output that
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are sometimes the same for one pair and different for another pair.
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* pairs that differed by one bit, by two bits, in any combination
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of top bits of (a,b,c), or in any combination of bottom bits of
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* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
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the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
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is commonly produced by subtraction) look like a single 1-bit
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* the base values were pseudorandom, all zero but one bit set, or
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all zero plus a counter that starts at zero.
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Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
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Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
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for "differ" defined as + with a one-bit base and a two-bit delta. I
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used http://burtleburtle.net/bob/hash/avalanche.html to choose
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the operations, constants, and arrangements of the variables.
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This does not achieve avalanche. There are input bits of (a,b,c)
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that fail to affect some output bits of (a,b,c), especially of a. The
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most thoroughly mixed value is c, but it doesn't really even achieve
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This allows some parallelism. Read-after-writes are good at doubling
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the number of bits affected, so the goal of mixing pulls in the opposite
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direction as the goal of parallelism. I did what I could. Rotates
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seem to cost as much as shifts on every machine I could lay my hands
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on, and rotates are much kinder to the top and bottom bits, so I used
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-------------------------------------------------------------------------------
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a -= c; a ^= rot(c, 4); c += b; \
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b -= a; b ^= rot(a, 6); a += c; \
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c -= b; c ^= rot(b, 8); b += a; \
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a -= c; a ^= rot(c,16); c += b; \
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b -= a; b ^= rot(a,19); a += c; \
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c -= b; c ^= rot(b, 4); b += a; \
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-------------------------------------------------------------------------------
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final -- final mixing of 3 32-bit values (a,b,c) into c
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Pairs of (a,b,c) values differing in only a few bits will usually
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produce values of c that look totally different. This was tested for
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* pairs that differed by one bit, by two bits, in any combination
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of top bits of (a,b,c), or in any combination of bottom bits of
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* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
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the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
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is commonly produced by subtraction) look like a single 1-bit
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* the base values were pseudorandom, all zero but one bit set, or
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all zero plus a counter that starts at zero.
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These constants passed:
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and these came close:
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-------------------------------------------------------------------------------
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#define final(a,b,c) \
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c ^= b; c -= rot(b,14); \
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a ^= c; a -= rot(c,11); \
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b ^= a; b -= rot(a,25); \
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c ^= b; c -= rot(b,16); \
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a ^= c; a -= rot(c,4); \
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b ^= a; b -= rot(a,14); \
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c ^= b; c -= rot(b,24); \
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-------------------------------------------------------------------------------
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hashlittle() -- 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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length : the length of the key, counting by bytes
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val2 : IN: can be any 4-byte value OUT: second 32 bit hash.
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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. Two keys differing by one or two bits will have
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totally different hash values. Note that the return value is better
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mixed than val2, so use that first.
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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 (uint8_t **)k, do it like this:
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for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
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By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
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code any way you wish, private, educational, or commercial. It's free.
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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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static uint32_t hashlittle( const void *key, size_t length )
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uint32_t a,b,c; /* internal state */
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union { const void *ptr; size_t i; } u; /* needed for Mac Powerbook G4 */
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/* Set up the internal state */
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a = b = c = 0xdeadbeef + ((uint32_t)length);
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if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
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const uint32_t *k = (const uint32_t *)key; /* read 32-bit chunks */
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/*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
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/*----------------------------- handle the last (probably partial) block */
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* "k[2]&0xffffff" actually reads beyond the end of the string, but
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* then masks off the part it's not allowed to read. Because the
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* string is aligned, the masked-off tail is in the same word as the
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* rest of the string. Every machine with memory protection I've seen
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* does it on word boundaries, so is OK with this. But VALGRIND will
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* still catch it and complain. The masking trick does make the hash
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* noticably faster for short strings (like English words).
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case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
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case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
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case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
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case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
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case 8 : b+=k[1]; a+=k[0]; break;
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case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
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case 6 : b+=k[1]&0xffff; a+=k[0]; break;
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case 5 : b+=k[1]&0xff; a+=k[0]; break;
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case 4 : a+=k[0]; break;
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case 3 : a+=k[0]&0xffffff; break;
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case 2 : a+=k[0]&0xffff; break;
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case 1 : a+=k[0]&0xff; break;
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case 0 : return c; /* zero length strings require no mixing */
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#else /* make valgrind happy */
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k8 = (const uint8_t *)k;
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case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
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case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
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case 10: c+=((uint32_t)k8[9])<<8; /* fall through */
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case 9 : c+=k8[8]; /* fall through */
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case 8 : b+=k[1]; a+=k[0]; break;
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case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
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case 6 : b+=((uint32_t)k8[5])<<8; /* fall through */
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case 5 : b+=k8[4]; /* fall through */
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case 4 : a+=k[0]; break;
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case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
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case 2 : a+=((uint32_t)k8[1])<<8; /* fall through */
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case 1 : a+=k8[0]; break;
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#endif /* !valgrind */
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} else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
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const uint16_t *k = (const uint16_t *)key; /* read 16-bit chunks */
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/*--------------- all but last block: aligned reads and different mixing */
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a += k[0] + (((uint32_t)k[1])<<16);
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b += k[2] + (((uint32_t)k[3])<<16);
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c += k[4] + (((uint32_t)k[5])<<16);
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/*----------------------------- handle the last (probably partial) block */
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k8 = (const uint8_t *)k;
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case 12: c+=k[4]+(((uint32_t)k[5])<<16);
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b+=k[2]+(((uint32_t)k[3])<<16);
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a+=k[0]+(((uint32_t)k[1])<<16);
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case 11: c+=((uint32_t)k8[10])<<16; /* fall through */
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b+=k[2]+(((uint32_t)k[3])<<16);
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a+=k[0]+(((uint32_t)k[1])<<16);
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case 9 : c+=k8[8]; /* fall through */
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case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
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a+=k[0]+(((uint32_t)k[1])<<16);
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case 7 : b+=((uint32_t)k8[6])<<16; /* fall through */
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a+=k[0]+(((uint32_t)k[1])<<16);
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case 5 : b+=k8[4]; /* fall through */
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case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
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case 3 : a+=((uint32_t)k8[2])<<16; /* fall through */
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case 0 : return c; /* zero length requires no mixing */
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} else { /* need to read the key one byte at a time */
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const uint8_t *k = (const uint8_t *)key;
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/*--------------- all but the last block: affect some 32 bits of (a,b,c) */
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a += ((uint32_t)k[1])<<8;
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a += ((uint32_t)k[2])<<16;
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a += ((uint32_t)k[3])<<24;
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b += ((uint32_t)k[5])<<8;
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b += ((uint32_t)k[6])<<16;
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b += ((uint32_t)k[7])<<24;
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c += ((uint32_t)k[9])<<8;
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c += ((uint32_t)k[10])<<16;
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c += ((uint32_t)k[11])<<24;
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/*-------------------------------- last block: affect all 32 bits of (c) */
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switch(length) /* all the case statements fall through */
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case 12: c+=((uint32_t)k[11])<<24;
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case 11: c+=((uint32_t)k[10])<<16;
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case 10: c+=((uint32_t)k[9])<<8;
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case 8 : b+=((uint32_t)k[7])<<24;
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case 7 : b+=((uint32_t)k[6])<<16;
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case 6 : b+=((uint32_t)k[5])<<8;
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case 4 : a+=((uint32_t)k[3])<<24;
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case 3 : a+=((uint32_t)k[2])<<16;
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case 2 : a+=((uint32_t)k[1])<<8;
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_PUBLIC_ unsigned int tdb_jenkins_hash(TDB_DATA *key)
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return hashlittle(key->dptr, key->dsize);