[pfdietz]

I'm talking about constructing boolean circuits. The usual parallel prefix algorithm yields a circuit of depth O(log n) with O(n log n) gates. Using some trickery, however, this can be reduced to O(n) gates, with a constant factor increase in depth.

https://en.wikipedia.org/wiki/Prefix_sum https://en.wikipedia.org/wiki/Adder_(electronics)

[ithkuil]

Constant depth requires unbounded fan-in, which may not be available in practice

[pfdietz]

Yes, I was talking about using gates of bounded fan-in.