Dumb Simple Slow Luhn Test.

gistfile1.txt

// A very simple Luhn check that only accepts sequence of digits as input.
// it scans the entire string with windows of 14,15,16 in width looking for a sequence that passes
// the luhn check. If it finds one it prints the original and the masked sequence, returning the 
// masked sequence. If none are found, the original is returned.
// This is a dumb, slow, checker only intended to validate test sequences more quickly than doing
// manually. It outputs the progress to allow human validation.


	public static String dumbSlowChecker(String test) {
		char[] c = test.toCharArray();
		if (c.length < 14) {
			return test;
		}
		System.err.println("String is "+test.length());
		for (int start = 0; start < c.length - 13; start++) {
			for (int end = start + 14; end < (Math.min(start+16, c.length)+1); end++) {
				int acc = 0;
				System.err.println("From "+(end-1)+" to "+start+" (inclusive) length "+(end-start));
				int n = 0;
				for (int i = end - 1; i >= start; i--) {
					int dv = c[i] - '0';
					if (n % 2 == 1) {
						dv = dv * 2;
						acc += dv / 10;
						acc += dv % 10;
						System.err.println(i+" C = "+c[i]+" x2 "+dv/10+" "+dv%10+" Acc = "+acc);
					} else {
						acc += dv;
						System.err.println(i+" C = "+c[i]+" x1 "+dv+"   Acc = "+acc);
					}
					n++;
				}
				if (acc % 10 == 0) {
					for (int i = start; i < end; i++) {
						c[i] = 'X';
					}
					System.err.println(test);
					System.err.println(new String(c));
					return new String(c);
				}
			}
		}
		return test;
	}