A pure PHP implementation of a Bloom Filter

1.0.2 2018-03-03 21:16 UTC


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This is a well tested implementation of a Bloom Filter for PHP. It has the following features:

  1. Efficient memory use for bit array (as efficient as PHP can be anyway).
  2. A way to get a raw version of the filter for transport to other systems.
  3. Ability to restore said raw filter back into a usable one.
  4. Auto-calculates optimal hashing and bit array size based on desired set size and false-positive probability.
  5. Auto-generates hashing functions as needed.


Install via Composer (make sure you have composer in your path or in your project).

Put the following in your package.json:

    "require": {
        "pleonasm/bloom-filter": "*"

Run composer install.


use Pleo\BloomFilter\BloomFilter;

$approximateItemCount = 100000;
$falsePositiveProbability = 0.001;

$before = memory_get_usage();
$bf = BloomFilter::init($approximateItemCount, $falsePositiveProbability);
$after = memory_get_usage();
// if this were a 100,000 item array, we would be looking at about 4MB of
// space used instead of the 200k or so this uses.
echo ($after - $before) . "\n";


$bf->exists('item1'); // true
$bf->exists('item2'); // true
$bf->exists('item3'); // true

// The following call will return false with a 0.1% probability of
// being true as long as the amount of items in the filter are < 100000
$bf->exists('non-existing-item'); // false

$serialized = json_encode($bf); // you can store/transfer this places!

// Re-hydrate the object this way.
$bf = BloomFilter::initFromJson(json_decode($serialized, true));

$bf->exists('item1'); // still true
$bf->exists('item2'); // still true
$bf->exists('item3'); // still true
$bf->exists('non-existing-item'); // still false

Warnings On Serialization

As a note: using json_encode() on a bloom filter object should work across most systems. You can run in to trouble if are moving the filter between 64 and 32 bit systems (that will outright not work) or moving between little-endian and big-endian systems (that should work, but I haven't tested it).

Also note that json_encode() will take the binary bit array and base64 encode it. So if you have a large array, it will get about 33% bigger on serialization.


This project requires PHP 5.4 or newer.


You can find the license for this code in the LICENSE file.