Inverting [or rather: negating] a number: what's quickest?

Guess what? Apparently the atmega328 used in most Arduinos does have hardware multiplication support!

● Advanced RISC architecture
● 131 powerful instructions – most single clock cycle execution
● 32  8 general purpose working registers
● Fully static operation
● Up to 16MIPS throughput at 16MHz
On-chip 2-cycle multiplier

But as I suspected, it takes 2 cycles, where subtraction will only take one cycle.