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https://github.com/bitcoin/bitcoin.git
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44 lines
1.2 KiB
Python
44 lines
1.2 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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def bn2mpi(v):
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"""Convert number to MPI format, without the sign byte."""
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# The top bit is used to indicate the sign of the number. If there
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# isn't a spare bit in the bit length, add an extension byte.
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have_ext = False
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ext = bytearray()
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if v.bit_length() > 0:
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have_ext = (v.bit_length() & 0x07) == 0
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ext.append(0)
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# Is the number negative?
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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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# Convert the int to bytes
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v_bin = bytearray()
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bytes_len = (v.bit_length() + 7) // 8
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for i in range(bytes_len, 0, -1):
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v_bin.append((v >> ((i - 1) * 8)) & 0xff)
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# Add the sign bit if necessary
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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 ext + v_bin
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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(reversed(bn2mpi(v)))
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