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#!/usr/bin/env python3
#
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.
"""Big number routines.
This file is copied from python-bitcoinlib.
"""
import struct
# generic big endian MPI format
def bn_bytes(v, have_ext=False):
ext = 0
if have_ext:
ext = 1
return ((v.bit_length()+7)//8) + ext
def bn2bin(v):
s = bytearray()
i = bn_bytes(v)
while i > 0:
s.append((v >> ((i-1) * 8)) & 0xff)
i -= 1
return s
def bin2bn(s):
l = 0
for ch in s:
l = (l << 8) | ch
return l
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
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
def mpi2vch(s):
r = s[4:] # strip size
r = r[::-1] # reverse string, converting BE->LE
return r
def bn2vch(v):
return bytes(mpi2vch(bn2mpi(v)))
def vch2mpi(s):
r = struct.pack(b">I", len(s)) # size
r += s[::-1] # reverse string, converting LE->BE
return r
def vch2bn(s):
return mpi2bn(vch2mpi(s))
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