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# -*- test-case-name: twisted.conch.test.test_ssh -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Common functions for the SSH classes.

Maintainer: Paul Swartz
"""

from __future__ import absolute_import, division

import struct

from cryptography.utils import int_from_bytes, int_to_bytes

from twisted.python.compat import unicode
from twisted.python.deprecate import deprecated
from twisted.python.versions import Version

__all__ = ["NS", "getNS", "MP", "getMP", "ffs"]



def NS(t):
    """
    net string
    """
    if isinstance(t, unicode):
        t = t.encode("utf-8")
    return struct.pack('!L', len(t)) + t



def getNS(s, count=1):
    """
    get net string
    """
    ns = []
    c = 0
    for i in range(count):
        l, = struct.unpack('!L', s[c:c + 4])
        ns.append(s[c + 4:4 + l + c])
        c += 4 + l
    return tuple(ns) + (s[c:],)



def MP(number):
    if number == 0:
        return b'\000' * 4
    assert number > 0
    bn = int_to_bytes(number)
    if ord(bn[0:1]) & 128:
        bn = b'\000' + bn
    return struct.pack('>L', len(bn)) + bn



def getMP(data, count=1):
    """
    Get multiple precision integer out of the string.  A multiple precision
    integer is stored as a 4-byte length followed by length bytes of the
    integer.  If count is specified, get count integers out of the string.
    The return value is a tuple of count integers followed by the rest of
    the data.
    """
    mp = []
    c = 0
    for i in range(count):
        length, = struct.unpack('>L', data[c:c + 4])
        mp.append(int_from_bytes(data[c + 4:c + 4 + length], 'big'))
        c += 4 + length
    return tuple(mp) + (data[c:],)



def _MPpow(x, y, z):
    """
    Return the MP version of C{(x ** y) % z}.
    """
    return MP(pow(x, y, z))



def ffs(c, s):
    """
    first from second
    goes through the first list, looking for items in the second, returns the first one
    """
    for i in c:
        if i in s:
            return i



@deprecated(Version("Twisted", 16, 5, 0))
def install():
    # This used to install gmpy, but is technically public API, so just do
    # nothing.
    pass