Given a component, compute its outputs from its inputs, which must already be evaluated. Outputs and inputs are both contained as time sequences in arrays. This function will calculate simStep outputs from (previously calculated) simStep outputs and clocked (simStep-1) outputs. Memory has state separate from simStep-1 output, for this the state is recalculated. Inputs and outputs come from either UInt32Step or BigIntStep arrays in IOArray record.

fastReduce for a one-off reduction, working out the step indices for itself. Anything reducing many components, or the same component over many steps, should compute them once with simStepOf and simStepOldOf and call fastReduce directly.