[AnimalMuppet]

How is the zero flag one NOR gate? Don't you have to NOR all the bits?

[bonzini]

One very large NOR gate. But unlike XOR, an n-bit NOR or NAND is just 2n transistors in CMOS (at least in theory).

[STM32F030R8]

One biiiig NOR gate.

[kens]

Yes, one 8-bit wide NOR gate. This is easy to implement in NMOS, basically you have a wire the width of the ALU and attach a transistor driven by each bit to pull it low.