def popcount(w):
"""
Create a population count circuit.
Parameters
----------
w: the width of the adder.
Returns
-------
a `CircuitGraph` addder.
"""
c = Circuit(name="popcount")
ps = [[c.add(f"in_{i}", "input")] for i in range(w)]
i = 0
while len(ps) > 1:
# get values
ns = ps.pop(0)
ms = ps.pop(0)
# pad
aw = max(len(ns), len(ms))
while len(ms) < aw:
ms += ["null"]
while len(ns) < aw:
ns += ["null"]
# instantiate and connect adder
a = adder(aw).strip_io()
c.extend(a.relabel({n: f"add_{i}_{n}" for n in a.nodes()}))
for j, (n, m) in enumerate(zip(ns, ms)):
c.connect(n, f"add_{i}_a_{j}")
c.connect(m, f"add_{i}_b_{j}")
# add adder outputs
ps.append([f"add_{i}_out_{j}" for j in range(aw + 1)])
i += 1
# connect outputs
for i, o in enumerate(ps[0]):
c.add(f"out_{i}", "buf", fanin=o, output=True)
if "null" in c:
c.set_type("null", "0")
c.set_output("null", False)
return c
def comb_ff():
lm = Circuit(name="ff")
# mux
m = mux(2).strip_io()
lm.extend(m.relabel({n: f"mux_{n}" for n in m.nodes()}))
# inputs
lm.add("si", "input", fanout="mux_in_0")
lm.add("d", "input", fanout="mux_in_1")
lm.add("clk", "input", fanout="mux_sel_0")
lm.add("r", "input")
lm.add("s", "input")
# logic
lm.add("r_b", "not", fanin="r")
lm.add("qr", "and", fanin=["mux_out", "r_b"])
lm.add("q", "or", fanin=["qr", "s"], output=True)
lm.add("so", "buf", fanin="q", output=True)
return lm