sipRound example

            $m = array(
                self::load_4(self::substr($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 )

        while ($left >= 8) {
            # m = LOAD64_LE( in );             $m = ParagonIE_Sodium_Core32_Int64::fromReverseString(
                self::substr($in, 0, 8)
            );

            # v3 ^= m;             $v[3] = $v[3]->xorInt64($m);

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

            # v0 ^= m;             $v[0] = $v[0]->xorInt64($m);

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

        # switch( left )         # {