We need some tools, in the form of software. We search for software that can be obtained without cost.
We use a Linux computer with Ubuntu 16.04, and a Mac computer with OS X El Capitan.
We decide to use Icarus Verilog.
We can install Icarus Verilog in Ubuntu, by doing
sudo apt-get install iverilog
We can install Icarus Verilog on Mac, by downloading its source code from this Icarus Verilog FTP repository.
The file verilog-20150513.tar.gz can be downloaded from the pre-v10 directory. The source can then be extracted and built, using the commands
tar xvf verilog-20150513.tar.gz cd verilog-20150513 ./configure make sudo make install