ParagonIE_Sodium_Core_SipHash::sipHash24

    public static function sipHash24($in, $key)
    {
        $inlen = self::strlen($in);

        # /* "somepseudorandomlygeneratedbytes" */
        # u64 v0 = 0x736f6d6570736575ULL;
        # u64 v1 = 0x646f72616e646f6dULL;
        # u64 v2 = 0x6c7967656e657261ULL;
        # u64 v3 = 0x7465646279746573ULL;
        $v = array(
            0x736f6d65, // 0
            0x70736575, // 1
            0x646f7261, // 2
            0x6e646f6d, // 3
            0x6c796765, // 4
            0x6e657261, // 5
            0x74656462, // 6
            0x79746573  // 7
        );
        // v0 => $v[0], $v[1]
        // v1 => $v[2], $v[3]
        // v2 => $v[4], $v[5]
        // v3 => $v[6], $v[7]

        # u64 k0 = LOAD64_LE( k );
        # u64 k1 = LOAD64_LE( k + 8 );
        $k = array(
            self::load_4(self::substr($key, 4, 4)),
            self::load_4(self::substr($key, 0, 4)),
            self::load_4(self::substr($key, 12, 4)),
            self::load_4(self::substr($key, 8, 4))
        );
        // k0 => $k[0], $k[1]
        // k1 => $k[2], $k[3]

        # b = ( ( u64 )inlen ) << 56;
        $b = array(
            $inlen << 24,
            0
        );
        // See docblock for why the 0th index gets the higher bits.

        # v3 ^= k1;
        $v[6] ^= $k[2];
        $v[7] ^= $k[3];
        # v2 ^= k0;
        $v[4] ^= $k[0];
        $v[5] ^= $k[1];
        # v1 ^= k1;
        $v[2] ^= $k[2];
        $v[3] ^= $k[3];
        # v0 ^= k0;
        $v[0] ^= $k[0];
        $v[1] ^= $k[1];

        $left = $inlen;
        # for ( ; in != end; in += 8 )
        while ($left >= 8) {
            # m = LOAD64_LE( in );
            $m = array(
                self::load_4(self::substr($in, 4, 4)),
                self::load_4(self::substr($in, 0, 4))
            );

            # v3 ^= m;
            $v[6] ^= $m[0];
            $v[7] ^= $m[1];

            # SIPROUND;
            # SIPROUND;
            $v = self::sipRound($v);
            $v = self::sipRound($v);

            # v0 ^= m;
            $v[0] ^= $m[0];
            $v[1] ^= $m[1];

            $in = self::substr($in, 8);
            $left -= 8;
        }

        # switch( left )
        #  {
        #     case 7: b |= ( ( u64 )in[ 6] )  << 48;
        #     case 6: b |= ( ( u64 )in[ 5] )  << 40;
        #     case 5: b |= ( ( u64 )in[ 4] )  << 32;
        #     case 4: b |= ( ( u64 )in[ 3] )  << 24;
        #     case 3: b |= ( ( u64 )in[ 2] )  << 16;
        #     case 2: b |= ( ( u64 )in[ 1] )  <<  8;
        #     case 1: b |= ( ( u64 )in[ 0] ); break;
        #     case 0: break;
        # }
        switch ($left) {
            case 7:
                $b[0] |= self::chrToInt($in[6]) << 16;
            case 6:
                $b[0] |= self::chrToInt($in[5]) << 8;
            case 5:
                $b[0] |= self::chrToInt($in[4]);
            case 4:
                $b[1] |= self::chrToInt($in[3]) << 24;
            case 3:
                $b[1] |= self::chrToInt($in[2]) << 16;
            case 2:
                $b[1] |= self::chrToInt($in[1]) << 8;
            case 1:
                $b[1] |= self::chrToInt($in[0]);
            case 0:
                break;
        }
        // See docblock for why the 0th index gets the higher bits.

        # v3 ^= b;
        $v[6] ^= $b[0];
        $v[7] ^= $b[1];

        # SIPROUND;
        # SIPROUND;
        $v = self::sipRound($v);
        $v = self::sipRound($v);

        # v0 ^= b;
        $v[0] ^= $b[0];
        $v[1] ^= $b[1];

        // Flip the lower 8 bits of v2 which is ($v[4], $v[5]) in our implementation
        # v2 ^= 0xff;
        $v[5] ^= 0xff;

        # SIPROUND;
        # SIPROUND;
        # SIPROUND;
        # SIPROUND;
        $v = self::sipRound($v);
        $v = self::sipRound($v);
        $v = self::sipRound($v);
        $v = self::sipRound($v);

        # b = v0 ^ v1 ^ v2 ^ v3;
        # STORE64_LE( out, b );
        return  self::store32_le($v[1] ^ $v[3] ^ $v[5] ^ $v[7]) .
            self::store32_le($v[0] ^ $v[2] ^ $v[4] ^ $v[6]);
    }