It is the CIC filter with Hogenauer pruning. This project is based on https://opencores.org/projects/cic_core project.
Differences are listed below:
/rtl/verilog/integrator.sv - integrator of CIC filter
/sim/rtl_sim/run/cic_d_run_sim.sh - script to run simulation with Icarus Verilog
Icarus Verilog is used for simulation GTKWave is used for watching the results of simulation
To see simulation results run /sim/rtl_sim/bin/cic_d_run_sim.sh
open output .vcd file with GTKWave load list of signals to watch from cic_d_tb.gtkw