Is integer multiplier physically in integer unit or special function unit?

Question

I'm using McPAT, a tool for estimating CPU power, however, it seems the integer multiplier is counted as a special function unit. Why is that? Shouldnt it be in the integer unit instead? And shouldn't special function unit only be concerned with transcendental functions such as sin, cos, rcp?

Answer 1

Integer multiplication is often pipelined, making it take multiple cycles to complete. As such, breaking it out into its own functional unit allows other integer operations (e.g, add/sub and bitwise operations) to run in a single cycle, possibly even while a multiply is in flight.

It's certainly not true that it's always a separate functional unit, though! Some CPUs (even small ones, like the ARM Cortex-M3 and M4 microcontrollers) have single-cycle multiply, which could very well be handled as part of the same FU as other integer operations.