  We introduce the Composable Involution Delay Model (CIDM) for fast and
accurate digital simulation. It is based on the Involution Delay Model (IDM)
[F\"ugger et al., IEEE TCAD 2020], which has been shown to be the only existing
candidate for faithful glitch propagation known so far. In its present form,
however, it has shortcomings that limit its practical applicability and
utility. First, IDM delay predictions are conceptually based on discretizing
the analog signal waveforms using specific matching input and output
discretization threshold voltages. Unfortunately, they are difficult to
determine and typically different for interconnected gates. Second,
metastability and high-frequency oscillations in a real circuit could be
invisible in the IDM signal predictions. Our CIDM reduces the characterization
effort by allowing independent discretization thresholds, improves
composability and increases the modeling power by exposing canceled pulse
trains at the gate interconnect. We formally show that, despite these
improvements, the CIDM still retains the IDM's faithfulness, which is a
consequence of the mathematical properties of involution delay functions.
