Use PINx to toggle pins.

[timower]

Currently DirectIO uses a read, flip, write sequence to toggle output pins.
This can be done faster by using the PINx registers (on some targets?).
See section 14.2.2 of the ATMega328 manual:

14.2.2 Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruction can be used to toggle one single bit in a port.

[WestfW]

Toggle capability is also present in SAM and SAMD