lcsim is a library for facilitating the construction and simulation of complex logical circuits in Python.
A component is a logical gate (e.g. AND, OR, NOT, XOR). All of the basic
digital gates are already implemented in the lcsim.components package,
which includes AND, OR, XOR, NOT, NAND, NOR, and XNOR.
You can create your own gate, as long as it adheres to the guidelines
of 0 or more input slots and exactly 1 output bit, by subclassing
components.base.ComponentBase and implementing evaluate().
For example, the following gate will output 1 if the sum of all 4 input bits is odd, or 0 if the sum is even:
from lcsim.components import base
class ExampleGate(base.ComponentBase):
def __init__(self):
super(ExampleGate, self).__init__('example', 4)
def evaluate(self):
inputs = self.evaluate_inputs()
self.output_bit = sum(inputs) % 2A circuit is a network of connected gates that performs some operation on a sequence of input bits.
Circuits are meant to be built modularly from less complex parts. As an
example, consider the implementation of the SHA-1 block operation as a
circuit, taken from the lcsim.sha1.builder module:
def block_operation(chunk, h0, h1, h2, h3, h4):
"""
Returns (h0, h1, h2, h3, h4), the h-constants that result from running
the SHA-1 algorithm on one block.
"""
a, b, c, d, e = h0, h1, h2, h3, h4
w = create_words(chunk)
# Main loop here
for i in xrange(0, 80):
if 0 <= i <= 19:
# f = (b and c) or ((not b) and d)
b_and_c = bitwise_and_circuit(32)
connect_circuits(b, b_and_c, {x: x for x in xrange(0, 32)})
connect_circuits(c, b_and_c, {x: x + 32 for x in xrange(0, 32)})
not_b = bitwise_not_circuit(32)
connect_circuits(b, not_b, {x: x for x in xrange(0, 32)})
not_b_and_d = bitwise_and_circuit(32)
connect_circuits(not_b, not_b_and_d, {x: x for x in xrange(0, 32)})
connect_circuits(d, not_b_and_d, {x: x + 32 for x in xrange(0, 32)})
f = bitwise_or_circuit(32)
connect_circuits(b_and_c, f, {x: x for x in xrange(0, 32)})
connect_circuits(not_b_and_d, f, {x: x + 32 for x in xrange(0, 32)})
k = digital_source_int_circuit(0x5A827999, 32)
elif 20 <= i <= 39:
# f = b xor c xor d
b_xor_c = bitwise_xor_circuit(32)
connect_circuits(b, b_xor_c, {x: x for x in xrange(0, 32)})
connect_circuits(c, b_xor_c, {x: x + 32 for x in xrange(0, 32)})
f = bitwise_xor_circuit(32)
connect_circuits(b_xor_c, f, {x: x for x in xrange(0, 32)})
connect_circuits(d, f, {x: x + 32 for x in xrange(0, 32)})
k = digital_source_int_circuit(0x6ED9EBA1, 32)
elif 40 <= i <= 59:
# f = (b and c) or (b and d) or (c and d)
b_and_c = bitwise_and_circuit(32)
connect_circuits(b, b_and_c, {x: x for x in xrange(0, 32)})
connect_circuits(c, b_and_c, {x: x + 32 for x in xrange(0, 32)})
b_and_d = bitwise_and_circuit(32)
connect_circuits(b, b_and_d, {x: x for x in xrange(0, 32)})
connect_circuits(d, b_and_d, {x: x + 32 for x in xrange(0, 32)})
c_and_d = bitwise_and_circuit(32)
connect_circuits(c, c_and_d, {x: x for x in xrange(0, 32)})
connect_circuits(d, c_and_d, {x: x + 32 for x in xrange(0, 32)})
bnc_or_bnd = bitwise_or_circuit(32)
connect_circuits(b_and_c, bnc_or_bnd, {x: x for x in xrange(0, 32)})
connect_circuits(b_and_d, bnc_or_bnd, {x: x + 32 for x in xrange(0, 32)})
f = bitwise_or_circuit(32)
connect_circuits(bnc_or_bnd, f, {x: x for x in xrange(0, 32)})
connect_circuits(c_and_d, f, {x: x + 32 for x in xrange(0, 32)})
k = digital_source_int_circuit(0x8F1BBCDC, 32)
elif 60 <= i <= 79:
# f = b xor c xor d
b_xor_c = bitwise_xor_circuit(32)
connect_circuits(b, b_xor_c, {x: x for x in xrange(0, 32)})
connect_circuits(c, b_xor_c, {x: x + 32 for x in xrange(0, 32)})
f = bitwise_xor_circuit(32)
connect_circuits(b_xor_c, f, {x: x for x in xrange(0, 32)})
connect_circuits(d, f, {x: x + 32 for x in xrange(0, 32)})
k = digital_source_int_circuit(0xCA62C1D6, 32)
else:
raise Exception("Invalid word index in main loop!")
# (a leftrotate 5) + f
temp = ripple_adder_no_carry(32)
connect_circuits(a, temp, {x: x - 5 for x in xrange(5, 32)})
connect_circuits(a, temp, {x: x + 27 for x in xrange(0, 5)})
connect_circuits(f, temp, {x: x + 32 for x in xrange(0, 32)})
# result + e
temp2 = ripple_adder_no_carry(32)
connect_circuits(temp, temp2, {x: x for x in xrange(0, 32)})
connect_circuits(e, temp2, {x: x + 32 for x in xrange(0, 32)})
# result + k
temp = ripple_adder_no_carry(32)
connect_circuits(temp2, temp, {x: x for x in xrange(0, 32)})
connect_circuits(k, temp, {x: x + 32 for x in xrange(0, 32)})
# result + w[i]
temp2 = ripple_adder_no_carry(32)
connect_circuits(temp, temp2, {x: x for x in xrange(0, 32)})
connect_circuits(w[i][0], temp2, {x: y for (x, y) in izip(w[i][1], xrange(32, 64))})
# temp = (a leftrotate 5) + f + e + k + w[i]
temp = temp2
e = d
d = c
c = left_rotate(b, 30)
b = a
a = temp
h0_add = ripple_adder_no_carry(32)
connect_circuits(h0, h0_add, {i: i for i in xrange(0, 32)})
connect_circuits(a, h0_add, {i: i + 32 for i in xrange(0, 32)})
h1_add = ripple_adder_no_carry(32)
connect_circuits(h1, h1_add, {i: i for i in xrange(0, 32)})
connect_circuits(b, h1_add, {i: i + 32 for i in xrange(0, 32)})
h2_add = ripple_adder_no_carry(32)
connect_circuits(h2, h2_add, {i: i for i in xrange(0, 32)})
connect_circuits(c, h2_add, {i: i + 32 for i in xrange(0, 32)})
h3_add = ripple_adder_no_carry(32)
connect_circuits(h3, h3_add, {i: i for i in xrange(0, 32)})
connect_circuits(d, h3_add, {i: i + 32 for i in xrange(0, 32)})
h4_add = ripple_adder_no_carry(32)
connect_circuits(h4, h4_add, {i: i for i in xrange(0, 32)})
connect_circuits(e, h4_add, {i: i + 32 for i in xrange(0, 32)})
return h0_add, h1_add, h2_add, h3_add, h4_add
def create_words(chunk):
w = [None] * 80
for i in xrange(0, 16):
w[i] = (chunk, xrange(i * 32, i * 32 + 32))
for i in xrange(16, 80):
# w[i] = (w[i-3] xor w[i-8] xor w[i-14] xor w[i-16]) leftrotate 1
xtemp = bitwise_xor_circuit(32)
connect_circuits(w[i - 3][0], xtemp, {
x: y for (x, y) in izip(w[i - 3][1], xrange(0, 32))
})
connect_circuits(w[i - 8][0], xtemp, {
x: y for (x, y) in izip(w[i - 8][1], xrange(32, 64))
})
# result xor w[i - 14]
xtemp2 = bitwise_xor_circuit(32)
connect_circuits(xtemp, xtemp2, {x: x for x in xrange(0, 32)})
connect_circuits(w[i - 14][0], xtemp2, {
x: y for (x, y) in izip(w[i - 14][1], xrange(32, 64))
})
# result xor w[i - 16]
xtemp = bitwise_xor_circuit(32)
connect_circuits(xtemp2, xtemp, {x: x for x in xrange(0, 32)})
connect_circuits(w[i - 16][0], xtemp, {
x: y for (x, y) in izip(w[i - 16][1], xrange(32, 64))
})
# leftrotate 1
word = left_rotate(xtemp, 1)
w[i] = (word, xrange(0, 32))
return w