From 19060d93fe8d8f3747c9d315bbed9ddc8a846151 Mon Sep 17 00:00:00 2001
From: Jason Davies <jason@jasondavies.com>
Date: Thu, 8 Dec 2011 18:43:12 +0000
Subject: [PATCH] More mixing added to FNV-1a.

Lack of sufficient mixing was causing "wtf" to hash poorly in the second
hash function, and only map to one location instead of ten.
---
 bloomfilter.js           | 17 +++++++++++---
 package.json             |  2 +-
 test/bloomfilter-test.js | 51 +++++-----------------------------------
 3 files changed, 21 insertions(+), 49 deletions(-)

diff --git a/bloomfilter.js b/bloomfilter.js
index b261455..c248d8c 100644
--- a/bloomfilter.js
+++ b/bloomfilter.js
@@ -33,10 +33,10 @@
         a = fnv_1a(v),
         b = fnv_1a_b(a),
         i = -1,
-        x;
+        x = a % m;
     while (++i < k) {
-      x = (a + b * i) % m;
-      r[i] = x < 0 ? x + m : x;
+      r[i] = x < 0 ? (x + m) : x;
+      x = (x + b) % m;
     }
     return r;
   };
@@ -90,12 +90,23 @@
       a ^= c & 0xff;
       a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
     }
+    // From http://home.comcast.net/~bretm/hash/6.html
+    a += a << 13;
+    a ^= a >> 7;
+    a += a << 3;
+    a ^= a >> 17;
+    a += a << 5;
     return a & 0xffffffff;
   }
 
   // One additional iteration of FNV, given a hash.
   function fnv_1a_b(a) {
     a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
+    a += a << 13;
+    a ^= a >> 7;
+    a += a << 3;
+    a ^= a >> 17;
+    a += a << 5;
     return a & 0xffffffff;
   }
 })(typeof exports !== "undefined" ? exports : this);
diff --git a/package.json b/package.json
index 09b1fd0..d371b2e 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "bloomfilter",
-  "version": "0.0.7",
+  "version": "0.0.8",
   "description": "Fast bloom filter in JavaScript.",
   "keywords": [
     "bloom filter",
diff --git a/test/bloomfilter-test.js b/test/bloomfilter-test.js
index e84839c..3a9bc75 100644
--- a/test/bloomfilter-test.js
+++ b/test/bloomfilter-test.js
@@ -1,6 +1,7 @@
 var bf = require("../bloomfilter"),
     BloomFilter = bf.BloomFilter,
-    fnv_1a = bf.fnv_1a;
+    fnv_1a = bf.fnv_1a,
+    fnv_1a_b = bf.fnv_1a_b;
 
 var vows = require("vows"),
     assert = require("assert");
@@ -36,52 +37,12 @@ suite.addBatch({
       assert.equal(f.test(n1), true);
       assert.equal(f.test(n2), false);
       assert.equal(f.test(n3), false);
-    }
-  },
-  "fnv": {
-    "basic": function() {
-      // Test vectors from http://isthe.com/chongo/tech/comp/fnv/
-      assert.equal(fnv_1a(""),  0x811c9dc5 & 0xffffffff);
-      assert.equal(fnv_1a("a"), 0xe40c292c & 0xffffffff);
-      assert.equal(fnv_1a("b"), 0xe70c2de5 & 0xffffffff);
-      assert.equal(fnv_1a("c"), 0xe60c2c52 & 0xffffffff);
-      assert.equal(fnv_1a("d"), 0xe10c2473 & 0xffffffff);
-      assert.equal(fnv_1a("e"), 0xe00c22e0 & 0xffffffff);
-      assert.equal(fnv_1a("f"), 0xe30c2799 & 0xffffffff);
-      assert.equal(fnv_1a("fo"), 0x6222e842 & 0xffffffff);
-      assert.equal(fnv_1a("foo"), 0xa9f37ed7 & 0xffffffff);
-      assert.equal(fnv_1a("foob"), 0x3f5076ef & 0xffffffff);
-      assert.equal(fnv_1a("fooba"), 0x39aaa18a & 0xffffffff);
-      assert.equal(fnv_1a("foobar"), 0xbf9cf968 & 0xffffffff);
-      assert.equal(fnv_1a("ch"), 0x5f299f4e & 0xffffffff);
-      assert.equal(fnv_1a("cho"), 0xef8580f3 & 0xffffffff);
-      assert.equal(fnv_1a("chon"), 0xac297727 & 0xffffffff);
-      assert.equal(fnv_1a("chong"), 0x4546b9c0 & 0xffffffff);
-      assert.equal(fnv_1a("chongo"), 0xbd564e7d & 0xffffffff);
-      assert.equal(fnv_1a("chongo "), 0x6bdd5c67 & 0xffffffff);
-      assert.equal(fnv_1a("chongo w"), 0xdd77ed30 & 0xffffffff);
-      assert.equal(fnv_1a("chongo wa"), 0xf4ca9683 & 0xffffffff);
-      assert.equal(fnv_1a("chongo was"), 0x4aeb9bd0 & 0xffffffff);
-      assert.equal(fnv_1a("chongo was "), 0xe0e67ad0 & 0xffffffff);
-      assert.equal(fnv_1a("chongo was h"), 0xc2d32fa8 & 0xffffffff);
-      assert.equal(fnv_1a("chongo was he"), 0x7f743fb7 & 0xffffffff);
-      assert.equal(fnv_1a("chongo was her"), 0x6900631f & 0xffffffff);
-      assert.equal(fnv_1a("chongo was here"), 0xc59c990e & 0xffffffff);
-      assert.equal(fnv_1a("chongo was here!"), 0x448524fd & 0xffffffff);
-      assert.equal(fnv_1a("chongo was here!\n"), 0xd49930d5 & 0xffffffff);
-      assert.equal(fnv_1a(repeat(500, "\x00")), 0xfa823dd5 & 0xffffffff);
-      assert.equal(fnv_1a(repeat(500, "\x07")), 0x21a27271 & 0xffffffff);
-      assert.equal(fnv_1a(repeat(500, "~")),    0x83c5c6d5 & 0xffffffff);
-      assert.equal(fnv_1a(repeat(500, "\x7f")), 0x813b0881 & 0xffffffff);
+    },
+    "wtf": function() {
+      var f = new BloomFilter(20, 10);
+      assert.equal(f.locations("wtf").length, 10);
     }
   }
 });
 
 suite.export(module);
-
-function repeat(n, d) {
-  var r = [],
-      i = -1;
-  while (++i < n) r[i] = d;
-  return r.join("");
-}