693 lines
17 KiB
C
693 lines
17 KiB
C
/*-------------------------------------------------------------------------
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*
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* hashfn.c
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* Generic hashing functions, and hash functions for use in dynahash.c
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* hashtables
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*
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*
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* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/common/hashfn.c
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*
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* NOTES
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* It is expected that every bit of a hash function's 32-bit result is
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* as random as every other; failure to ensure this is likely to lead
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* to poor performance of hash tables. In most cases a hash
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* function should use hash_bytes() or its variant hash_bytes_uint32(),
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* or the wrappers hash_any() and hash_uint32 defined in hashfn.h.
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "common/hashfn.h"
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#include "port/pg_bitutils.h"
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/*
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* This hash function was written by Bob Jenkins
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* (bob_jenkins@burtleburtle.net), and superficially adapted
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* for PostgreSQL by Neil Conway. For more information on this
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* hash function, see http://burtleburtle.net/bob/hash/doobs.html,
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* or Bob's article in Dr. Dobb's Journal, Sept. 1997.
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*
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* In the current code, we have adopted Bob's 2006 update of his hash
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* function to fetch the data a word at a time when it is suitably aligned.
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* This makes for a useful speedup, at the cost of having to maintain
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* four code paths (aligned vs unaligned, and little-endian vs big-endian).
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* It also uses two separate mixing functions mix() and final(), instead
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* of a slower multi-purpose function.
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*/
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/* Get a bit mask of the bits set in non-uint32 aligned addresses */
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#define UINT32_ALIGN_MASK (sizeof(uint32) - 1)
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#define rot(x,k) pg_rotate_left32(x, k)
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/*----------
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* mix -- mix 3 32-bit values reversibly.
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*
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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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*
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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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* 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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* (a,b,c).
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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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* difference.
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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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*
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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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* avalanche in c.
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*
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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 from 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 on,
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* and rotates are much kinder to the top and bottom bits, so I used rotates.
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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 -= 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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/*----------
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* final -- final mixing of 3 32-bit values (a,b,c) into c
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*
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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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* (a,b,c).
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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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* difference.
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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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*
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* The use of separate functions for mix() and final() allow for a
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* substantial performance increase since final() does not need to
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* do well in reverse, but is does need to affect all output bits.
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* mix(), on the other hand, does not need to affect all output
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* bits (affecting 32 bits is enough). The original hash function had
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* a single mixing operation that had to satisfy both sets of requirements
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* and was slower as a result.
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*----------
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*/
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#define final(a,b,c) \
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{ \
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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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/*
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* hash_bytes() -- 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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*
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* Returns a uint32 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 6*len+35 instructions. The best hash table sizes are powers
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* of 2. There is no need to do mod a prime (mod is sooo slow!).
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* If you need less than 32 bits, use a bitmask.
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*
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* This procedure must never throw elog(ERROR); the ResourceOwner code
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* relies on this not to fail.
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*
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* Note: we could easily change this function to return a 64-bit hash value
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* by using the final values of both b and c. b is perhaps a little less
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* well mixed than c, however.
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*/
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uint32
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hash_bytes(const unsigned char *k, int keylen)
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{
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uint32 a,
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b,
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c,
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len;
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/* Set up the internal state */
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len = keylen;
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a = b = c = 0x9e3779b9 + len + 3923095;
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/* If the source pointer is word-aligned, we use word-wide fetches */
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if (((uintptr_t) k & UINT32_ALIGN_MASK) == 0)
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{
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/* Code path for aligned source data */
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const uint32 *ka = (const uint32 *) k;
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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 += ka[0];
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b += ka[1];
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c += ka[2];
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mix(a, b, c);
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ka += 3;
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len -= 12;
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}
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/* handle the last 11 bytes */
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k = (const unsigned char *) ka;
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#ifdef WORDS_BIGENDIAN
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 8);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 24);
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/* fall through */
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case 8:
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/* the lowest byte of c is reserved for the length */
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b += ka[1];
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a += ka[0];
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break;
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case 7:
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b += ((uint32) k[6] << 8);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 16);
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/* fall through */
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case 5:
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b += ((uint32) k[4] << 24);
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/* fall through */
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case 4:
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a += ka[0];
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break;
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case 3:
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a += ((uint32) k[2] << 8);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 16);
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/* fall through */
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case 1:
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a += ((uint32) k[0] << 24);
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/* case 0: nothing left to add */
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}
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#else /* !WORDS_BIGENDIAN */
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 24);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 8);
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/* fall through */
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case 8:
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/* the lowest byte of c is reserved for the length */
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b += ka[1];
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a += ka[0];
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break;
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case 7:
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b += ((uint32) k[6] << 16);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 8);
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/* fall through */
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case 5:
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b += k[4];
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/* fall through */
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case 4:
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a += ka[0];
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break;
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case 3:
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a += ((uint32) k[2] << 16);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 8);
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/* fall through */
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case 1:
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a += k[0];
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/* case 0: nothing left to add */
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}
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#endif /* WORDS_BIGENDIAN */
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}
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else
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{
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/* Code path for non-aligned source data */
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/* handle most of the key */
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while (len >= 12)
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{
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#ifdef WORDS_BIGENDIAN
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a += (k[3] + ((uint32) k[2] << 8) + ((uint32) k[1] << 16) + ((uint32) k[0] << 24));
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b += (k[7] + ((uint32) k[6] << 8) + ((uint32) k[5] << 16) + ((uint32) k[4] << 24));
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c += (k[11] + ((uint32) k[10] << 8) + ((uint32) k[9] << 16) + ((uint32) k[8] << 24));
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#else /* !WORDS_BIGENDIAN */
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a += (k[0] + ((uint32) k[1] << 8) + ((uint32) k[2] << 16) + ((uint32) k[3] << 24));
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b += (k[4] + ((uint32) k[5] << 8) + ((uint32) k[6] << 16) + ((uint32) k[7] << 24));
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c += (k[8] + ((uint32) k[9] << 8) + ((uint32) k[10] << 16) + ((uint32) k[11] << 24));
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#endif /* WORDS_BIGENDIAN */
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mix(a, b, c);
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k += 12;
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len -= 12;
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}
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/* handle the last 11 bytes */
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#ifdef WORDS_BIGENDIAN
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 8);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 24);
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/* fall through */
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case 8:
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/* the lowest byte of c is reserved for the length */
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b += k[7];
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/* fall through */
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case 7:
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b += ((uint32) k[6] << 8);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 16);
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/* fall through */
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case 5:
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b += ((uint32) k[4] << 24);
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/* fall through */
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case 4:
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a += k[3];
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/* fall through */
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case 3:
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a += ((uint32) k[2] << 8);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 16);
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/* fall through */
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case 1:
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a += ((uint32) k[0] << 24);
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/* case 0: nothing left to add */
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}
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#else /* !WORDS_BIGENDIAN */
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 24);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 8);
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/* fall through */
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case 8:
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/* the lowest byte of c is reserved for the length */
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b += ((uint32) k[7] << 24);
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/* fall through */
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case 7:
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b += ((uint32) k[6] << 16);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 8);
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/* fall through */
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case 5:
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b += k[4];
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/* fall through */
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case 4:
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a += ((uint32) k[3] << 24);
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/* fall through */
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case 3:
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a += ((uint32) k[2] << 16);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 8);
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/* fall through */
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case 1:
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a += k[0];
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/* case 0: nothing left to add */
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}
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#endif /* WORDS_BIGENDIAN */
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}
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final(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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* hash_bytes_extended() -- hash into a 64-bit value, using an optional seed
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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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* seed : a 64-bit seed (0 means no seed)
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*
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* Returns a uint64 value. Otherwise similar to hash_bytes.
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*/
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uint64
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hash_bytes_extended(const unsigned char *k, int keylen, uint64 seed)
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{
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uint32 a,
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b,
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c,
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len;
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/* Set up the internal state */
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len = keylen;
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a = b = c = 0x9e3779b9 + len + 3923095;
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/* If the seed is non-zero, use it to perturb the internal state. */
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if (seed != 0)
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{
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/*
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* In essence, the seed is treated as part of the data being hashed,
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* but for simplicity, we pretend that it's padded with four bytes of
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* zeroes so that the seed constitutes a 12-byte chunk.
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*/
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a += (uint32) (seed >> 32);
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b += (uint32) seed;
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mix(a, b, c);
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}
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/* If the source pointer is word-aligned, we use word-wide fetches */
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if (((uintptr_t) k & UINT32_ALIGN_MASK) == 0)
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{
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/* Code path for aligned source data */
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const uint32 *ka = (const uint32 *) k;
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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 += ka[0];
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b += ka[1];
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c += ka[2];
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mix(a, b, c);
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ka += 3;
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len -= 12;
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}
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/* handle the last 11 bytes */
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k = (const unsigned char *) ka;
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#ifdef WORDS_BIGENDIAN
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 8);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 24);
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/* fall through */
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case 8:
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/* the lowest byte of c is reserved for the length */
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b += ka[1];
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a += ka[0];
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break;
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case 7:
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b += ((uint32) k[6] << 8);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 16);
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/* fall through */
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case 5:
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b += ((uint32) k[4] << 24);
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/* fall through */
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case 4:
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a += ka[0];
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break;
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case 3:
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a += ((uint32) k[2] << 8);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 16);
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/* fall through */
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case 1:
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a += ((uint32) k[0] << 24);
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/* case 0: nothing left to add */
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}
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#else /* !WORDS_BIGENDIAN */
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 24);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 8);
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/* fall through */
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case 8:
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/* the lowest byte of c is reserved for the length */
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b += ka[1];
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a += ka[0];
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break;
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case 7:
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b += ((uint32) k[6] << 16);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 8);
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/* fall through */
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case 5:
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b += k[4];
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/* fall through */
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case 4:
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a += ka[0];
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break;
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case 3:
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a += ((uint32) k[2] << 16);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 8);
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/* fall through */
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case 1:
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a += k[0];
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/* case 0: nothing left to add */
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}
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#endif /* WORDS_BIGENDIAN */
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}
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else
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{
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/* Code path for non-aligned source data */
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/* handle most of the key */
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while (len >= 12)
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{
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#ifdef WORDS_BIGENDIAN
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a += (k[3] + ((uint32) k[2] << 8) + ((uint32) k[1] << 16) + ((uint32) k[0] << 24));
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b += (k[7] + ((uint32) k[6] << 8) + ((uint32) k[5] << 16) + ((uint32) k[4] << 24));
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c += (k[11] + ((uint32) k[10] << 8) + ((uint32) k[9] << 16) + ((uint32) k[8] << 24));
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#else /* !WORDS_BIGENDIAN */
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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));
|
|
#endif /* WORDS_BIGENDIAN */
|
|
mix(a, b, c);
|
|
k += 12;
|
|
len -= 12;
|
|
}
|
|
|
|
/* handle the last 11 bytes */
|
|
#ifdef WORDS_BIGENDIAN
|
|
switch (len)
|
|
{
|
|
case 11:
|
|
c += ((uint32) k[10] << 8);
|
|
/* fall through */
|
|
case 10:
|
|
c += ((uint32) k[9] << 16);
|
|
/* fall through */
|
|
case 9:
|
|
c += ((uint32) k[8] << 24);
|
|
/* fall through */
|
|
case 8:
|
|
/* the lowest byte of c is reserved for the length */
|
|
b += k[7];
|
|
/* fall through */
|
|
case 7:
|
|
b += ((uint32) k[6] << 8);
|
|
/* fall through */
|
|
case 6:
|
|
b += ((uint32) k[5] << 16);
|
|
/* fall through */
|
|
case 5:
|
|
b += ((uint32) k[4] << 24);
|
|
/* fall through */
|
|
case 4:
|
|
a += k[3];
|
|
/* fall through */
|
|
case 3:
|
|
a += ((uint32) k[2] << 8);
|
|
/* fall through */
|
|
case 2:
|
|
a += ((uint32) k[1] << 16);
|
|
/* fall through */
|
|
case 1:
|
|
a += ((uint32) k[0] << 24);
|
|
/* case 0: nothing left to add */
|
|
}
|
|
#else /* !WORDS_BIGENDIAN */
|
|
switch (len)
|
|
{
|
|
case 11:
|
|
c += ((uint32) k[10] << 24);
|
|
/* fall through */
|
|
case 10:
|
|
c += ((uint32) k[9] << 16);
|
|
/* fall through */
|
|
case 9:
|
|
c += ((uint32) k[8] << 8);
|
|
/* fall through */
|
|
case 8:
|
|
/* the lowest byte of c is reserved for the length */
|
|
b += ((uint32) k[7] << 24);
|
|
/* fall through */
|
|
case 7:
|
|
b += ((uint32) k[6] << 16);
|
|
/* fall through */
|
|
case 6:
|
|
b += ((uint32) k[5] << 8);
|
|
/* fall through */
|
|
case 5:
|
|
b += k[4];
|
|
/* fall through */
|
|
case 4:
|
|
a += ((uint32) k[3] << 24);
|
|
/* fall through */
|
|
case 3:
|
|
a += ((uint32) k[2] << 16);
|
|
/* fall through */
|
|
case 2:
|
|
a += ((uint32) k[1] << 8);
|
|
/* fall through */
|
|
case 1:
|
|
a += k[0];
|
|
/* case 0: nothing left to add */
|
|
}
|
|
#endif /* WORDS_BIGENDIAN */
|
|
}
|
|
|
|
final(a, b, c);
|
|
|
|
/* report the result */
|
|
return ((uint64) b << 32) | c;
|
|
}
|
|
|
|
/*
|
|
* hash_bytes_uint32() -- hash a 32-bit value to a 32-bit value
|
|
*
|
|
* This has the same result as
|
|
* hash_bytes(&k, sizeof(uint32))
|
|
* but is faster and doesn't force the caller to store k into memory.
|
|
*/
|
|
uint32
|
|
hash_bytes_uint32(uint32 k)
|
|
{
|
|
uint32 a,
|
|
b,
|
|
c;
|
|
|
|
a = b = c = 0x9e3779b9 + (uint32) sizeof(uint32) + 3923095;
|
|
a += k;
|
|
|
|
final(a, b, c);
|
|
|
|
/* report the result */
|
|
return c;
|
|
}
|
|
|
|
/*
|
|
* hash_bytes_uint32_extended() -- hash 32-bit value to 64-bit value, with seed
|
|
*
|
|
* Like hash_bytes_uint32, this is a convenience function.
|
|
*/
|
|
uint64
|
|
hash_bytes_uint32_extended(uint32 k, uint64 seed)
|
|
{
|
|
uint32 a,
|
|
b,
|
|
c;
|
|
|
|
a = b = c = 0x9e3779b9 + (uint32) sizeof(uint32) + 3923095;
|
|
|
|
if (seed != 0)
|
|
{
|
|
a += (uint32) (seed >> 32);
|
|
b += (uint32) seed;
|
|
mix(a, b, c);
|
|
}
|
|
|
|
a += k;
|
|
|
|
final(a, b, c);
|
|
|
|
/* report the result */
|
|
return ((uint64) b << 32) | c;
|
|
}
|
|
|
|
/*
|
|
* string_hash: hash function for keys that are NUL-terminated strings.
|
|
*
|
|
* NOTE: this is the default hash function if none is specified.
|
|
*/
|
|
uint32
|
|
string_hash(const void *key, Size keysize)
|
|
{
|
|
/*
|
|
* If the string exceeds keysize-1 bytes, we want to hash only that many,
|
|
* because when it is copied into the hash table it will be truncated at
|
|
* that length.
|
|
*/
|
|
Size s_len = strlen((const char *) key);
|
|
|
|
s_len = Min(s_len, keysize - 1);
|
|
return hash_bytes((const unsigned char *) key, (int) s_len);
|
|
}
|
|
|
|
/*
|
|
* tag_hash: hash function for fixed-size tag values
|
|
*/
|
|
uint32
|
|
tag_hash(const void *key, Size keysize)
|
|
{
|
|
return hash_bytes((const unsigned char *) key, (int) keysize);
|
|
}
|
|
|
|
/*
|
|
* uint32_hash: hash function for keys that are uint32 or int32
|
|
*
|
|
* (tag_hash works for this case too, but is slower)
|
|
*/
|
|
uint32
|
|
uint32_hash(const void *key, Size keysize)
|
|
{
|
|
Assert(keysize == sizeof(uint32));
|
|
return hash_bytes_uint32(*((const uint32 *) key));
|
|
}
|