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61 lines
1.5 KiB
Python
61 lines
1.5 KiB
Python
#!/usr/bin/env python3
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#
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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"""Big number routines.
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Functions for converting numbers to MPI format and Bitcoin-specific little
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endian format.
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This file is copied from python-bitcoinlib.
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"""
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import struct
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def bn_bytes(v, have_ext=False):
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"""Return number of bytes in integer representation of v."""
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ext = 0
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if have_ext:
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ext = 1
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return (v.bit_length() + 7) // 8 + ext
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def bn2bin(v):
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"""Convert a number to a byte array."""
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s = bytearray()
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i = bn_bytes(v)
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while i > 0:
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s.append((v >> ((i - 1) * 8)) & 0xff)
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i -= 1
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return s
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def bn2mpi(v):
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"""Convert number to MPI format."""
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have_ext = False
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if v.bit_length() > 0:
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have_ext = (v.bit_length() & 0x07) == 0
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neg = False
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if v < 0:
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neg = True
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v = -v
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s = struct.pack(b">I", bn_bytes(v, have_ext))
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ext = bytearray()
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if have_ext:
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ext.append(0)
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v_bin = bn2bin(v)
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if neg:
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if have_ext:
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ext[0] |= 0x80
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else:
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v_bin[0] |= 0x80
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return s + ext + v_bin
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def mpi2vch(s):
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"""Convert MPI format to bitcoin-specific little endian format, with implicit size."""
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r = s[4:] # strip size
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r = r[::-1] # reverse string, converting BE->LE
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return r
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def bn2vch(v):
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"""Convert number to bitcoin-specific little endian format."""
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return bytes(mpi2vch(bn2mpi(v)))
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