megautil.py

import base64
import binascii
import struct


def base64urldecode(data):
    data += '=='[(2 - len(data) * 3) % 4:]
    for search, replace in (('-', '+'), ('_', '/'), (',', '')):
        data = data.replace(search, replace)
    return base64.b64decode(data)


def base64urlencode(data):
    data = base64.b64encode(data)
    for search, replace in (('+', '-'), ('/', '_'), ('=', '')):
        data = data.replace(search, replace)
    return data


def a32_to_str(a):
    return struct.pack('>%dI' % len(a), *a)


def str_to_a32(b):
    if len(b) % 4:
        b += '\0' * (4 - len(b) % 4)
    return struct.unpack('>%dI' % (len(b) / 4), b)


def a32_to_base64(a):
    return base64urlencode(a32_to_str(a))


def base64_to_a32(s):
    return str_to_a32(base64urldecode(s))


def mpi2int(s):
    return int(binascii.hexlify(s[2:]), 16)


def get_chunks(size):
    chunks = {}
    p = pp = 0
    i = 1

    while i <= 8 and p < size - i * 0x20000:
      chunks[p] = i * 0x20000
      pp = p
      p += chunks[p]
      i += 1

    while p < size:
      chunks[p] = 0x100000
      pp = p
      p += chunks[p]

    chunks[pp] = size - pp
    if not chunks[pp]:
      del chunks[pp]

    return chunks