piece spec hash implementation in php

piece_spec_hash.php

<?php
  error_reporting(E_ALL);

  class AV {
    function __construct($id, $qualifier_1, $qualifier_2) {
      $this->id = $id;
      $this->qualifier_1 = $qualifier_1;
      $this->qualifier_2 = $qualifier_2;
    }

    public function components() {
       return array(pack_64be($this->id), $this->qualifier_1, $this->qualifier_2);
     }

    public function hash_62bit() {
      $sha256 = hash_init("sha256");

      foreach ($this->components() as $component) {
        hash_update($sha256, hash("sha256", $component, true));
      }

      return unpack_64be(hash_final($sha256, true))[1] & 0x3fffffffffffffff;
    }
  }

  function pack_64be($value) {
    return pack("N", ($value >> 32)) . pack("N", 0xffffffff & $value);
  }

  function unpack_64be($value) {
    $ints = unpack("N2", $value);
    return array(1 => ($ints[1] << 32) + $ints[2]);
  }

  function piece_spec_hash($sku_id, $avs) {
    if (count($avs) == 0) {
      return $sku_id;
    }

    $av_hashes = array_unique(array_map(function($av) { return $av->hash_62bit(); }, $avs));
    sort($av_hashes);

    $sha256 = hash_init("sha256");
    hash_update($sha256, pack_64be($sku_id));

    foreach ($av_hashes as $hash) {
      hash_update($sha256, pack_64be($hash));
    }

    return unpack("N", hash_final($sha256, true))[1];
  }

  $avs = array(
    new AV(4242, "", ""),
    new AV(2, "qualifier 1 value", "qualifier 2 value")
  );

  echo "av1 62-bit hash: " . $avs[0]->hash_62bit() . "\n";
  echo "av2 62-bit hash: " . $avs[1]->hash_62bit() . "\n";
  echo "piece_spec_hash: " . piece_spec_hash(88662, $avs) . "\n";
?>