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Mildly improved (?) quasi-hash for deterministic treap construction

This commit is contained in:
Tony Garnock-Jones 2014-07-18 22:28:32 -07:00
parent 2fd7a07fe0
commit 91246c1471
1 changed files with 14 additions and 2 deletions
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16
minimart/treap.rkt
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@ -64,8 +64,20 @@
(define (treap-empty? t) (zero? (treap-size t)))
(define (default-priority key)
(bitwise-xor 609512461 ;; a random number
(equal-hash-code key)))
;; Loosely based on a restriction of murmur32 v3
(define c1 #xcc9e2d51)
(define c2 #x1b873593)
(define r1 15)
(define r2 13)
(define m 5)
(define n #xe6546b64)
(define k (* (equal-hash-code key) c1))
(define hash0 (* c2 (bitwise-ior (arithmetic-shift k r1) (arithmetic-shift k (- 32 r1)))))
(define hash1
(+ n (* m (bitwise-ior (arithmetic-shift hash0 r2) (arithmetic-shift hash0 (- 32 r2))))))
(define hash2 (* #x85ebca6b (bitwise-xor hash1 (arithmetic-shift hash1 -16))))
(define hash3 (* #xc2b2ae35 (bitwise-xor hash2 (arithmetic-shift hash1 -13))))
(bitwise-xor hash2 (arithmetic-shift hash1 -16)))
(define (treap-insert t key value [priority (default-priority key)])
(match-define (treap order root oldsize) t)