def int2vec(num, length=None):
"""Convert a signed integer to a BitVector."""
if num < 0:
req_length = clog2(abs(num)) + 1
bv = uint2vec(2 ** req_length + num)
else:
req_length = clog2(num + 1) + 1
bv = uint2vec(num, req_length)
if length:
if length < req_length:
raise ValueError("overflow: " + str(num))
else:
bv.sext(length - req_length)
return bv
def kogge_stone_add(A, B, cin=0):
"""Return symbolic logic for an N-bit Kogge-Stone adder."""
assert len(A) == len(B)
stop = len(A)
# generate/propagate logic
g = [A[i] * B[i] for i in range(stop)]
p = [Xor(A[i], B[i]) for i in range(stop)]
for i in range(clog2(stop)):
start = 1 << i
for j in range(start, stop):
g[j] = g[j] + p[j] * g[j-start]
p[j] = p[j] * p[j-start]
# sum logic
s = [Xor(A[i], B[i], (cin if i == 0 else g[i-1])) for i in range(stop)]
return BitVector(s), BitVector(g)
