Курнат Андрей
213 lines
11 KiB
C
213 lines
11 KiB
C
/*
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* c_jhash.c Jenkins Hash
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*
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* Copyright (c) 1997 Bob Jenkins <bob_jenkins@burtleburtle.net>
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*
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* lookup8.c, by Bob Jenkins, January 4 1997, Public Domain.
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* hash(), hash2(), hash3, and _c_mix() are externally useful functions.
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* Routines to test the hash are included if SELF_TEST is defined.
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* You can use this free for any purpose. It has no warranty.
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*
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* See http://burtleburtle.net/bob/hash/evahash.html
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*/
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/**
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* @file common/c_jhash.h
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*
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* @brief Interface of the cynapses jhash implementation
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*
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* @defgroup cynJHashInternals cynapses libc jhash function
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* @ingroup cynLibraryAPI
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*
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* @{
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*/
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#ifndef _C_JHASH_H
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#define _C_JHASH_H
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#include <QtCore/qglobal.h>
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#include <stdint.h>
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/**
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* _c_mix64 -- Mix 3 64-bit values reversibly.
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*
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* _c_mix64() takes 48 machine instructions, but only 24 cycles on a superscalar
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* machine (like Intel's new MMX architecture). It requires 4 64-bit
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* registers for 4::2 parallelism.
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* All 1-bit deltas, all 2-bit deltas, all deltas composed of top bits of
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* (a,b,c), and all deltas of bottom bits were tested. All deltas were
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* tested both on random keys and on keys that were nearly all zero.
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* These deltas all cause every bit of c to change between 1/3 and 2/3
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* of the time (well, only 113/400 to 287/400 of the time for some
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* 2-bit delta). These deltas all cause at least 80 bits to change
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* among (a,b,c) when the _c_mix is run either forward or backward (yes it
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* is reversible).
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* This implies that a hash using _c_mix64 has no funnels. There may be
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* characteristics with 3-bit deltas or bigger, I didn't test for
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* those.
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*/
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#define _c_mix64(a, b, c) \
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{ \
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a -= b; \
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a -= c; \
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a ^= (c >> 43); \
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b -= c; \
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b -= a; \
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b ^= (a << 9); \
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c -= a; \
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c -= b; \
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c ^= (b >> 8); \
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a -= b; \
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a -= c; \
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a ^= (c >> 38); \
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b -= c; \
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b -= a; \
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b ^= (a << 23); \
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c -= a; \
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c -= b; \
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c ^= (b >> 5); \
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a -= b; \
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a -= c; \
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a ^= (c >> 35); \
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b -= c; \
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b -= a; \
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b ^= (a << 49); \
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c -= a; \
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c -= b; \
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c ^= (b >> 11); \
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a -= b; \
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a -= c; \
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a ^= (c >> 12); \
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b -= c; \
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b -= a; \
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b ^= (a << 18); \
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c -= a; \
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c -= b; \
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c ^= (b >> 22); \
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}
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/**
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* @brief hash a variable-length key into a 64-bit value
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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 64 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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* Use for hash table lookup, or anything where one collision in 2^^64
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* is acceptable. Do NOT use for cryptographic purposes.
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*
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* @param k The key (the unaligned variable-length array of bytes).
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* @param length The length of the key, counting by bytes.
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* @param intval Initial value, can be any 8-byte value.
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*
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* @return A 64-bit value. Every bit of the key affects every bit of
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* the return value. No funnels. Every 1-bit and 2-bit delta
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* achieves avalanche. About 41+5len instructions.
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*/
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static inline uint64_t c_jhash64(const uint8_t *k, uint64_t length, uint64_t intval)
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{
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uint64_t 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 = intval; /* the previous hash value */
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c = 0x9e3779b97f4a7c13LL; /* the golden ratio; an arbitrary value */
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/* handle most of the key */
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while (len >= 24) {
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a += (k[0] + ((uint64_t)k[1] << 8) + ((uint64_t)k[2] << 16) + ((uint64_t)k[3] << 24) + ((uint64_t)k[4] << 32) + ((uint64_t)k[5] << 40)
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+ ((uint64_t)k[6] << 48) + ((uint64_t)k[7] << 56));
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b += (k[8] + ((uint64_t)k[9] << 8) + ((uint64_t)k[10] << 16) + ((uint64_t)k[11] << 24) + ((uint64_t)k[12] << 32) + ((uint64_t)k[13] << 40)
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+ ((uint64_t)k[14] << 48) + ((uint64_t)k[15] << 56));
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c += (k[16] + ((uint64_t)k[17] << 8) + ((uint64_t)k[18] << 16) + ((uint64_t)k[19] << 24) + ((uint64_t)k[20] << 32) + ((uint64_t)k[21] << 40)
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+ ((uint64_t)k[22] << 48) + ((uint64_t)k[23] << 56));
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_c_mix64(a, b, c);
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k += 24;
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len -= 24;
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}
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/* handle the last 23 bytes */
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c += length;
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switch (len) {
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case 23:
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c += ((uint64_t)k[22] << 56);
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Q_FALLTHROUGH();
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case 22:
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c += ((uint64_t)k[21] << 48);
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Q_FALLTHROUGH();
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case 21:
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c += ((uint64_t)k[20] << 40);
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Q_FALLTHROUGH();
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case 20:
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c += ((uint64_t)k[19] << 32);
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Q_FALLTHROUGH();
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case 19:
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c += ((uint64_t)k[18] << 24);
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Q_FALLTHROUGH();
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case 18:
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c += ((uint64_t)k[17] << 16);
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Q_FALLTHROUGH();
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case 17:
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c += ((uint64_t)k[16] << 8);
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Q_FALLTHROUGH();
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/* the first byte of c is reserved for the length */
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case 16:
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b += ((uint64_t)k[15] << 56);
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Q_FALLTHROUGH();
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case 15:
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b += ((uint64_t)k[14] << 48);
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Q_FALLTHROUGH();
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case 14:
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b += ((uint64_t)k[13] << 40);
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Q_FALLTHROUGH();
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case 13:
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b += ((uint64_t)k[12] << 32);
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Q_FALLTHROUGH();
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case 12:
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b += ((uint64_t)k[11] << 24);
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Q_FALLTHROUGH();
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case 11:
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b += ((uint64_t)k[10] << 16);
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Q_FALLTHROUGH();
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case 10:
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b += ((uint64_t)k[9] << 8);
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Q_FALLTHROUGH();
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case 9:
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b += ((uint64_t)k[8]);
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Q_FALLTHROUGH();
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case 8:
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a += ((uint64_t)k[7] << 56);
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Q_FALLTHROUGH();
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case 7:
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a += ((uint64_t)k[6] << 48);
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Q_FALLTHROUGH();
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case 6:
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a += ((uint64_t)k[5] << 40);
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Q_FALLTHROUGH();
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case 5:
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a += ((uint64_t)k[4] << 32);
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Q_FALLTHROUGH();
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case 4:
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a += ((uint64_t)k[3] << 24);
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Q_FALLTHROUGH();
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case 3:
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a += ((uint64_t)k[2] << 16);
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Q_FALLTHROUGH();
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case 2:
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a += ((uint64_t)k[1] << 8);
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Q_FALLTHROUGH();
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case 1:
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a += ((uint64_t)k[0]);
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/* case 0: nothing left to add */
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}
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_c_mix64(a, b, c);
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return c;
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}
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/**
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* }@
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*/
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#endif /* _C_JHASH_H */
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