Four bit adder: Difference between revisions

=={{header|Python}}==

<lang python>def xor(a, b): return (a and not b) or (b and not a)

def ha(a, b): return xor(a, b), a and b # sum, carry

def fa(a, b, ci):

s0, c0 = ha(ci, a)

s1, c1 = ha(s0, b)

return s1, c0 or c1 # sum, carry

def fa4(a, b):

width = 4

ci = [0] * width

co = [0] * width

s = [0] * width

for i in range(width):

s[i], co[i] = fa(a[i], b[i], co[i-1] if i else 0)

return s, co[-1]

def int2bus(n, width=4):

return [int(c) for c in "{0:0{1}b}".format(n, width)[::-1]]

def bus2int(b):

return sum(1 << i for i, bit in enumerate(b) if bit)

def test_fa4():

width = 4

tot = [None] * (width + 1)

for a in range(2**width):

for b in range(2**width):

tot[:width], tot[width] = fa4(int2bus(a), int2bus(b))

assert a + b == bus2int(tot), "totals don't match: %i + %i != %s" % (a, b, tot)

if __name__ == '__main__':

test_fa4()</lang>