implementing a crossover hash function

2012-06-02 12:07:26 +02:00
parent 87768f1a98
commit 3893ca44b9
5 changed files with 56 additions and 10 deletions
@@ -0,0 +1,17 @@
+(ns NoteHub.crossover.lib
+  (:refer-clojure :exclude [hash]))
+
+; very simple hash function %)
+; (doesn't work for UTF-16!)
+(defn hash [f s]
+  (let [short-mod #(mod % 32767)
+        ; we cannot use Math/pow because it's imprecise
+        ; and differs on JVM and JS
+        pow (fn [n e]
+              (reduce #(short-mod (* % %2)) 1
+                      (repeat e n)))
+        char-codes (map #(f (str %)) s)]
+    (reduce
+      #(short-mod (+ % 
+                     (short-mod (* (first %2) (pow 31 (second %2))))))
+      0 (map list char-codes (range)))))