istrain
559caead36
Public community release. The complete working system — DSP + decoders (scripts/), web dashboard + API (dashboard/), container stack (docker/), config templates (config/) — plus APOCALYPSE-EDITION.md, the full build guide for a human or a coding agent. GPLv3 (PyEOT dependency). Scrubbed of all secrets, internal IPs, hostnames, and location detail. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
79 lines
2.0 KiB
Python
79 lines
2.0 KiB
Python
#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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"""
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PyEOT End-of-Train Device Decoder
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Copyright (c) 2018 Eric Reuter
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This source file is subject of the GNU general public license.
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history: 2018-08-09 Initial Version
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purpose: Misc. functions used by eot_decoder.py
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Function XOR() and mod2div() adapted from:
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https://www.geeksforgeeks.org/cyclic-redundancy-check-python/
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"""
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# XOR two strings of bytes representing binary symbols
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def xor(a, b):
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result = []
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for i in range(len(b)):
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if a[i] == b[i]:
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result.append('0')
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else:
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result.append('1')
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return ''.join(result)
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# Reverse string
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def reverse(data):
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return ''.join(data[::-1])
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# Perform modulo-2 division on two strings of binary symbols
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def mod2div(dividend, divisor):
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# Number of bits to be XORed at a time.
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pick = len(divisor)
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# Slicing the dividend to appropriate
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# length for particular step
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tmp = dividend[0:pick]
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while pick < len(dividend):
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if tmp[0] == '1':
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# replace the dividend by the result
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# of XOR and pull 1 bit down
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tmp = xor(divisor[1:], tmp[1:]) + dividend[pick]
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else: # If leftmost bit is '0'
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# If the leftmost bit of the dividend (or the
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# part used in each step) is 0, the step cannot
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# use the regular divisor; we need to use an
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# all-0s divisor.
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tmp = xor(('0'*pick)[1:], tmp[1:]) + dividend[pick]
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# increment pick to move further
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pick += 1
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# For the last n bits, we have to carry it out
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# normally as increased value of pick will cause
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# Index Out of Bounds.
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if tmp[0] == '1':
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tmp = xor(divisor[1:], tmp[1:])
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else:
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tmp = xor(('0'*pick)[1:], tmp[1:])
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remainder = tmp
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return remainder
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# Calculate BCH checkbits
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def checkbits(data, key):
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appended_data = data + '0'*(len(key)-1) # Appends n-1 zeros at end of data
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remainder = mod2div(appended_data, key)
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return ''.join(remainder)
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