# Copyright (C) 2012-2014 The python-bitcoinlib developers
#
# This file is part of python-bitcoinlib.
#
# It is subject to the license terms in the LICENSE file found in the top-level
# directory of this distribution.
#
# No part of python-bitcoinlib, including this file, may be copied, modified,
# propagated, or distributed except according to the terms contained in the
# LICENSE file.
"""Bignum routines"""
from __future__ import absolute_import, division, print_function, unicode_literals
import struct
# generic big endian MPI format
[docs]def bn_bytes(v, have_ext=False):
ext = 0
if have_ext:
ext = 1
return ((v.bit_length() + 7) // 8) + ext
[docs]def bn2bin(v):
s = bytearray()
i = bn_bytes(v)
while i > 0:
s.append((v >> ((i - 1) * 8)) & 0xff)
i -= 1
return s
[docs]def bin2bn(s):
l = 0
for ch in s:
l = (l << 8) | ch
return l
[docs]def bn2mpi(v):
have_ext = False
if v.bit_length() > 0:
have_ext = (v.bit_length() & 0x07) == 0
neg = False
if v < 0:
neg = True
v = -v
s = struct.pack(b">I", bn_bytes(v, have_ext))
ext = bytearray()
if have_ext:
ext.append(0)
v_bin = bn2bin(v)
if neg:
if have_ext:
ext[0] |= 0x80
else:
v_bin[0] |= 0x80
return s + ext + v_bin
[docs]def mpi2bn(s):
if len(s) < 4:
return None
s_size = bytes(s[:4])
v_len = struct.unpack(b">I", s_size)[0]
if len(s) != (v_len + 4):
return None
if v_len == 0:
return 0
v_str = bytearray(s[4:])
neg = False
i = v_str[0]
if i & 0x80:
neg = True
i &= ~0x80
v_str[0] = i
v = bin2bn(v_str)
if neg:
return -v
return v
# bitcoin-specific little endian format, with implicit size
[docs]def mpi2vch(s):
r = s[4:] # strip size
r = r[::-1] # reverse string, converting BE->LE
return r
[docs]def bn2vch(v):
return bytes(mpi2vch(bn2mpi(v)))
[docs]def vch2mpi(s):
r = struct.pack(b">I", len(s)) # size
r += s[::-1] # reverse string, converting LE->BE
return r
[docs]def vch2bn(s):
return mpi2bn(vch2mpi(s))