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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.
Functions for converting numbers to MPI format and Bitcoin-specific little
endian format.
This file is copied from python-bitcoinlib.
"""
def bn_bytes(v):
"""Return number of bytes in integer representation of v."""
return (v.bit_length() + 7) // 8
def bn2bin(v):
"""Convert a number to a byte array."""
s = bytearray()
i = bn_bytes(v)
while i > 0:
s.append((v >> ((i - 1) * 8)) & 0xff)
i -= 1
return s
def bn2mpi(v):
"""Convert number to MPI format, without the sign byte."""
have_ext = False
if v.bit_length() > 0:
have_ext = (v.bit_length() & 0x07) == 0
neg = False
if v < 0:
neg = True
v = -v
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 ext + v_bin
def mpi2vch(s):
"""Convert MPI format to bitcoin-specific little endian format."""
return s[::-1] # reverse string, converting BE->LE
def bn2vch(v):
"""Convert number to bitcoin-specific little endian format."""
return bytes(mpi2vch(bn2mpi(v)))
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