Created
March 30, 2023 08:56
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| #!/usr/bin/env python3 | |
| """Toggle the bit at the specified offset. | |
| Syntax: <cmdname> filename bit-offset""" | |
| import sys | |
| import os | |
| import random | |
| fname = sys.argv[1] | |
| # Convert bit offset to bytes + leftover bits | |
| file_stats = os.stat(fname) | |
| total_bytes = file_stats.st_size | |
| total_bits = total_bytes * 8 | |
| target_bit = random.randrange(total_bits) | |
| nbytes = target_bit // 8 | |
| nbits = target_bit % 8 | |
| # Open in read+write, binary mode; read 1 byte | |
| fp = open(fname, "r+b") | |
| fp.seek(nbytes, 0) | |
| c = fp.read(1) | |
| # Toggle bit at byte position `nbits` | |
| toggled = bytes([ord(c) ^ (1 << nbits)]) | |
| # print(toggled) # diagnostic output | |
| # Back up one byte, write out the modified byte | |
| fp.seek(-1, 1) # or absolute: fp.seek(nbytes, 0) | |
| fp.write(toggled) | |
| fp.close() |
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