CLJ-1336 - make hashing mixing function available in Clojure for external collections. Add generative tests that check external hashing facilities match internal hashes.

Signed-off-by: Stuart Halloway <[email protected]>

Author: puredanger

src/clj/clojure/core.clj

@@ -4694,6 +4694,16 @@
    :static true}
   [x] (. clojure.lang.Util (hasheq x)))
 
+(defn mix-collection-hash
+  "Mix final collection hash for ordered or unordered collections.
+   hash-basis is the combined collection hash, count is the number
+   of elements included in the basis. Note this is the hash code
+   consistent with =, different from .hashCode.
+   See http://clojure.org/data_structures#hash for full algorithms."
+  {:added "1.6"
+   :static true}
+  [^long hash-basis count] (clojure.lang.Murmur3/mixCollHash hash-basis count))
+
 (defn interpose
   "Returns a lazy seq of the elements of coll separated by sep"
   {:added "1.0"

src/jvm/clojure/lang/Murmur3.java

@@ -91,7 +91,7 @@ public static int hashUnencodedChars(CharSequence input){
 	return fmix(h1, 2 * input.length());
 }
 
-public static int fixCollHash(int hash, int count){
+public static int mixCollHash(int hash, int count){
 	int h1 = seed;
 	int k1 = mixK1(hash);
 	h1 = mixH1(h1, k1);
@@ -108,7 +108,7 @@ public static int hashOrdered(Iterable xs){
 		++n;
 		}
 
-	return fixCollHash(hash, n);
+	return mixCollHash(hash, n);
 }
 
 public static int hashUnordered(Iterable xs){
@@ -120,7 +120,7 @@ public static int hashUnordered(Iterable xs){
 		++n;
 		}	
 
-	return fixCollHash(hash, n);
+	return mixCollHash(hash, n);
 }
 
 private static int mixK1(int k1){
@@ -148,4 +148,4 @@ private static int fmix(int h1, int length){
 	return h1;
 }
 
-}
+}

test/clojure/test_clojure/data_structures.clj

@@ -1074,3 +1074,38 @@
                                "Banana" "like", "apple" "love", "7th" "indifferent") ]]
     (doseq [m1 maps1, m2 maps1]
       (is-same-collection m1 m2))))
+
+;; *** Collection hashes ***
+;; See: http://clojure.org/data_structures#hash
+
+(defn hash-ordered [collection]
+  (-> (reduce (fn [acc e] (unchecked-add-int (unchecked-multiply-int 31 acc) (hash e)))
+              1
+              collection)
+      (mix-collection-hash (count collection))))
+
+(defn hash-unordered [collection]
+  (-> (reduce unchecked-add-int 0 (map hash collection))
+      (mix-collection-hash (count collection))))
+
+(defn gen-elements
+  []
+  (gen/vec gen/anything))
+
+(defspec ordered-collection-hashes-match
+  identity
+  [^{:tag clojure.test-clojure.data-structures/gen-elements} elem]
+  (let [v (vec elem)
+        l (apply list elem)]
+    (is (= (hash v)
+           (hash l)
+           (hash (map identity elem))
+           (hash-ordered elem)))))
+
+(defspec unordered-set-hashes-match
+  identity
+  [^{:tag clojure.test-clojure.data-structures/gen-elements} elem]
+  (let [unique-elem (distinct elem)
+        s (into #{} unique-elem)]
+    (is (= (hash s)
+           (hash-unordered unique-elem)))))