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56 lines
2.0 KiB
Python
56 lines
2.0 KiB
Python
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#!/usr/bin/env python3
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# Copyright (c) 2019 Pieter Wuille
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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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"""Utility functions related to output descriptors"""
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INPUT_CHARSET = "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ "
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CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
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GENERATOR = [0xf5dee51989, 0xa9fdca3312, 0x1bab10e32d, 0x3706b1677a, 0x644d626ffd]
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def descsum_polymod(symbols):
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"""Internal function that computes the descriptor checksum."""
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chk = 1
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for value in symbols:
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top = chk >> 35
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chk = (chk & 0x7ffffffff) << 5 ^ value
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for i in range(5):
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chk ^= GENERATOR[i] if ((top >> i) & 1) else 0
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return chk
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def descsum_expand(s):
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"""Internal function that does the character to symbol expansion"""
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groups = []
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symbols = []
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for c in s:
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if not c in INPUT_CHARSET:
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return None
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v = INPUT_CHARSET.find(c)
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symbols.append(v & 31)
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groups.append(v >> 5)
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if len(groups) == 3:
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symbols.append(groups[0] * 9 + groups[1] * 3 + groups[2])
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groups = []
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if len(groups) == 1:
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symbols.append(groups[0])
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elif len(groups) == 2:
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symbols.append(groups[0] * 3 + groups[1])
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return symbols
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def descsum_create(s):
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"""Add a checksum to a descriptor without"""
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symbols = descsum_expand(s) + [0, 0, 0, 0, 0, 0, 0, 0]
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checksum = descsum_polymod(symbols) ^ 1
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return s + '#' + ''.join(CHECKSUM_CHARSET[(checksum >> (5 * (7 - i))) & 31] for i in range(8))
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def descsum_check(s, require=True):
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"""Verify that the checksum is correct in a descriptor"""
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if not '#' in s:
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return not require
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if s[-9] != '#':
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return False
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if not all(x in CHECKSUM_CHARSET for x in s[-8:]):
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return False
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symbols = descsum_expand(s[:-9]) + [CHECKSUM_CHARSET.find(x) for x in s[-8:]]
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return descsum_polymod(symbols) == 1
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