Detect EPROM errors

pinerrors.py

import sys
import math
from collections import defaultdict

def inner_addresses(pin):
    for i in range(2**pin):
        yield i

def outer_addresses(pin, rom_size):
    gap = 2**(pin+1)
    addr = 0
    while addr < rom_size:
        yield addr
        addr += gap

for fn in sys.argv[1:]:
    print(fn)
    with open(fn, 'rb') as f:
        rom = f.read()

    rom_size = len(rom)
    max_pin = int(math.log(rom_size)/math.log(2))-1

    ratios = []

    for pin in range(max_pin+1):
        diff_count = 0
        match_count = 0
        for block in outer_addresses(pin, rom_size):
            for inner in inner_addresses(pin):
                if rom[block + inner] != rom[block + inner + 2**pin]:
                    diff_count += 1
                else:
                    match_count += 1

        ratio = float(match_count)/(diff_count+match_count)
        ratios.append((ratio, pin))

    for ratio, pin in sorted(ratios, reverse=True):
        broken_str = ''
        if ratio > 0.50:
            broken_str = ' (possibly broken)'

        print('A{} - {:.2f}% repeats{}'.format(pin, ratio*100, broken_str))

    print('')