Example #1
0
def multiply(x, y):
    """ Input: positive integers x and y, in binary
    output: their product """
    xlen = len(x)
    ylen = len(y)
    print "xlen:ylen :: ", xlen, ylen
    n = max(xlen, ylen)
    if n == 1:
        return str(int(x) * int(y))
    m = n/2
    xL, xR = x[:m], x[m:]
    yL, yR = y[:m], y[m:]

    P1 = multiply(xL, yL)
    P2 = multiply(xR, yR)
    P3 = multiply(binsum(xL, xR), binsum(yL, yR))
    # print "P1, P2, P3: ", P1, P2, P3
    P4 = binsum(P1, P2)
    print "P1, P2, P3, P4: ", P1, P2, P3, P4
    print "n, m: ", n, m
    a = P1 + ("0" * n)
    b = bin_subtract(P3, P4)
    b = b + ("0" * m)

    result = binsum(a, b)
    result = binsum(result, P2)
    # print ("maxlen is: ", maxlen)
    return result
Example #2
0
def two_complement(k):
    klen = len(k)
    result = []
    for i in range(klen):
        if int(k[i]) == 0:
            result.append('1')
        else:
            result.append('0')

    one = "1"
    result = ''.join(result)
    result = binsum(result, one)
    return result
Example #3
0
def bin_subtract(x, y):
    """ assumes x and y are binary strings """
    xlen = len(x)
    ylen = len(y)
    diff = abs(xlen - ylen)
    z = "0" * diff
    # print "Z: ", z
    if xlen > ylen:
        y = z + y
    elif xlen < ylen:
        x = z + x
    # print "X: ", x
    # print "Y: ", y
    yc = two_complement(y)
    # print "Y 2 complement: ", yc
    result = binsum(x, yc)
    result = result[1:]
    result = result.lstrip("0")
    # print "result: ", result
    return result