60 lines
1.4 KiB
JavaScript
60 lines
1.4 KiB
JavaScript
(function(exports) {
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function BloomFilter(m, k) {
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this.m = m;
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this.k = k;
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var buckets = this.buckets = [],
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n = Math.ceil(m / k),
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i = -1;
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while (++i < n) buckets[i] = 0;
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}
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// See http://willwhim.wordpress.com/2011/09/03/producing-n-hash-functions-by-hashing-only-once/
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BloomFilter.prototype.locations = function(v) {
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var k = this.k,
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m = this.m,
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r = [],
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n = v.length,
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a = 2166136261,
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b,
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c,
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i = -1;
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// Fowler/Noll/Vo hashing.
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while (++i < n) {
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c = v.charCodeAt(i);
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a ^= (c & 0xff00) >> 8;
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a *= 16777619;
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a ^= c & 0xff;
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a *= 16777619;
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}
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b = a * 16777619;
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i = -1; while (++i < k) r[i] = (a + b * i) % m;
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return r;
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};
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BloomFilter.prototype.add = function(v) {
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var l = this.locations(v),
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i = -1,
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k = this.k,
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buckets = this.buckets;
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while (++i < k) buckets[Math.floor(l[i] / k)] |= 1 << (l[i] % k)
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};
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BloomFilter.prototype.test = function(v) {
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var l = this.locations(v),
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n = l.length,
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i = -1,
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k = this.k,
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b,
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buckets = this.buckets;
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while (++i < n) {
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b = l[i];
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if ((buckets[Math.floor(b / k)] & (1 << (b % k))) === 0) {
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return false;
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}
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}
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return true;
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};
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exports.BloomFilter = BloomFilter;
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})(typeof exports !== "undefined" ? exports : this);
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