[List.External:Policy4]
int mask[0x100];

void init()
{
	int c;

	mask[0] = 0x100;
	c = 1;
	while (c < 0x100)
		mask[c++] = 0x80;

	c = 'a';
	while (c <= 'z')
		mask[c++] = 1;
	c = 'A';
	while (c <= 'Z')
		mask[c++] = 2;
	c = '0';
	while (c <= '9')
		mask[c++] = 4;
}

void filter()
{
	int i, seen;

/* This loop ends when we see NUL (sets 0x100) */
	i = seen = 0;
	while ((seen |= mask[word[i++]]) < 0x100)
		continue;

/*
 * We should have seen at least one character of each type (which "add up"
 * to 0x87) and then a NUL (adds 0x100).
 */
	if (seen != 0x187)
		word = 0; // Does not conform to policy
}