# Copyright (c) 2001-2004 Twisted Matrix Laboratories.
# See LICENSE for details.

# 

"""Common functions for the SSH classes.

This module is unstable.

Maintainer: U{Paul Swartz<mailto:z3p@twistedmatrix.com>}
"""

import struct
try:
    from Crypto import Util
    from Crypto.Util import randpool
except ImportError:
    import warnings
    warnings.warn("PyCrypto not installed, but continuing anyways!", 
            RuntimeWarning)
else:
    entropy = randpool.RandomPool()
    entropy.stir()


def NS(t):
    """
    net string
    """
    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 '\000'*4
    assert number>0
    bn = Util.number.long_to_bytes(number)
    if ord(bn[0])&128:
        bn = '\000' + bn
    return struct.pack('>L',len(bn)) + bn

def getMP(data):
    """
    get multiple precision integer
    """
    length=struct.unpack('>L',data[:4])[0]
    return Util.number.bytes_to_long(data[4:4+length]),data[4+length:]

def _MPpow(x, y, z):
    """return the MP version of (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

getMP_py = getMP
MP_py = MP
_MPpow_py = _MPpow
pyPow = pow

def _fastgetMP(i):
    l = struct.unpack('!L', i[:4])[0]
    n = i[4:l+4][::-1]
    return long(gmpy.mpz(n+'\x00', 256)), i[4+l:]

def _fastMP(i):
    i2 = gmpy.mpz(i).binary()[::-1]
    return struct.pack('!L', len(i2)) + i2

def _fastMPpow(x, y, z=None):
    r = pyPow(gmpy.mpz(x),y,z).binary()[::-1]
    return struct.pack('!L', len(r)) + r

def _fastpow(x, y, z=None):
    return pyPow(gmpy.mpz(x), y, z)

def install():
    global getMP, MP, _MPpow
    getMP = _fastgetMP
    MP = _fastMP
    _MPpow = _fastMPpow
    __builtins__['pow'] = _fastpow # evil evil
    
try:
    import gmpy
    install()
except ImportError:
    pass