test/functional/test_framework/bignum.py

   1 #!/usr/bin/env python3
   2 #
   3 # Distributed under the MIT software license, see the accompanying
   4 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5 """Big number routines.
   6
   7 This file is copied from python-bitcoinlib.
   8 """
   9
  10 import struct
  11
  12
  13 # generic big endian MPI format
  14
  15 def bn_bytes(v, have_ext=False):
  16     ext = 0
  17     if have_ext:
  18         ext = 1
  19     return ((v.bit_length()+7)//8) + ext
  20
  21 def bn2bin(v):
  22     s = bytearray()
  23     i = bn_bytes(v)
  24     while i > 0:
  25         s.append((v >> ((i-1) * 8)) & 0xff)
  26         i -= 1
  27     return s
  28
  29 def bn2mpi(v):
  30     have_ext = False
  31     if v.bit_length() > 0:
  32         have_ext = (v.bit_length() & 0x07) == 0
  33
  34     neg = False
  35     if v < 0:
  36         neg = True
  37         v = -v
  38
  39     s = struct.pack(b">I", bn_bytes(v, have_ext))
  40     ext = bytearray()
  41     if have_ext:
  42         ext.append(0)
  43     v_bin = bn2bin(v)
  44     if neg:
  45         if have_ext:
  46             ext[0] |= 0x80
  47         else:
  48             v_bin[0] |= 0x80
  49     return s + ext + v_bin
  50
  51 # bitcoin-specific little endian format, with implicit size
  52 def mpi2vch(s):
  53     r = s[4:]           # strip size
  54     r = r[::-1]         # reverse string, converting BE->LE
  55     return r
  56
  57 def bn2vch(v):
  58     return bytes(mpi2vch(bn2mpi(v)))