Two's Complement Hash Generation Code

def tohex(val, nbits):
  return hex((val + (1 << nbits)) % (1 << nbits))

def get_hex(sha):
    d = sha.digest()
    d = [ord(x) for x in d]

    #carry flag
    c = True

    #test for most significant bit
    n = (d[0] & 0x80) == 0x80

    if n:
        x = len(d)
        while x > 0:
            x -= 1
            d[x] = ~d[x]
            if c:
                c = d[x] == 0xFF
                d[x] = d[x]+1

    d = [tohex(x, 8)[tohex(x, 8).index('x')+1:] for x in d]

    d = ''.join(d)
    while d[0] == '0':
        d = d[1:]
    if n:
        d = '-'+d
    return d.lower()