Provides the 'vcd2df' function, which loads a IEEE 1364-1995/2001
VCD (.vcd) file, specified as a parameter of type string containing exactly
a file path, and returns an R dataframe containing values over time.
A VCD file captures the register values at discrete timepoints from a
simulated trace of execution of a hardware design in Verilog or VHDL.
The returned dataframe contains a row for each register, by name, and a
column for each time point, specified VCD-style using octothorpe-prefixed
multiples of the timescale as strings.
The only non-trivial implementation details are that (1) VCD 'x' and 'z'
non-numerical values are encoded as negative value -1 (as otherwise all bit
values are positive) and (2) registers with repeated names in distinct
modules are ignored, rather than duplicated, as we anticipate these
registers to have the same values.
Read more in arXiv preprint: 'vcd2df' -- Leveraging Data Science Insights
for Hardware Security Research