diff --git a/bloomfilter.js b/bloomfilter.js index a7ec421..47e06bf 100644 --- a/bloomfilter.js +++ b/bloomfilter.js @@ -8,26 +8,39 @@ while (++i < n) buckets[i] = 0; } + // Fowler/Noll/Vo hashing. + function fnv_1a(v) { + var n = v.length, + a = 2166136261, + c, + i = -1; + while (++i < n) { + c = v.charCodeAt(i); + a ^= (c & 0xff00) >> 8; + a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24); + a &= 0xffffffff; + a ^= c & 0xff; + a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24); + a &= 0xffffffff; + } + return a; + } + + // One additional iteration of FNV, given a hash. + function fnv_1a_b(a) { + a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24); + return a & 0xffffffff; + } + // See http://willwhim.wordpress.com/2011/09/03/producing-n-hash-functions-by-hashing-only-once/ BloomFilter.prototype.locations = function(v) { var k = this.k, m = this.m, r = [], - n = v.length, - a = 2166136261, - b, - c, + a = fnv_1a(v), + b = fnv_1a_b(a), i = -1; - // Fowler/Noll/Vo hashing. - while (++i < n) { - c = v.charCodeAt(i); - a ^= (c & 0xff00) >> 8; - a *= 16777619; - a ^= c & 0xff; - a *= 16777619; - } - b = a * 16777619; - i = -1; while (++i < k) r[i] = (a + b * i) % m; + while (++i < k) r[i] = (a + b * i) % m; return r; }; @@ -56,4 +69,6 @@ }; exports.BloomFilter = BloomFilter; + exports.fnv_1a = fnv_1a; + exports.fnv_1a_b = fnv_1a_b; })(typeof exports !== "undefined" ? exports : this);