25 lines
787 B
C
25 lines
787 B
C
#ifndef _LINUX_HASH_H
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#define _LINUX_HASH_H
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/* Fast hashing routine for ints, longs and pointers.
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(C) 2002 William Lee Irwin III, IBM */
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/*
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* Knuth recommends primes in approximately golden ratio to the maximum
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* integer representable by a machine word for multiplicative hashing.
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* Chuck Lever verified the effectiveness of this technique:
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* http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
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*
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* These primes are chosen to be bit-sparse, that is operations on
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* them can use shifts and additions instead of multiplications for
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* machines where multiplications are slow.
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*/
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#include <stdint.h>
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static inline uint64_t hash_64(const uint64_t val, const unsigned int bits)
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{
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return (val * 11400714819323198485LLU) >> (64 - bits);
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}
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#endif /* _LINUX_HASH_H */
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