Stuff

/*
 * This function adds a byte into the entropy pool.  It does not
 * update the entropy estimate.  The caller must do this if appropriate.
 *
 * The pool is stirred with a primitive polynomial of degree 128
 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
 *
 * We rotate the input word by a changing number of bits, to help
 * assure that all bits in the entropy get toggled.  Otherwise, if we
 * consistently feed the entropy pool small numbers (like jiffies and
 * scancodes, for example), the upper bits of the entropy pool don't
 * get affected. --- TYT, 10/11/95
 */
static void
add_entropy_words(buf, n)
	const u_int32_t *buf;
	u_int n;
{
	static const u_int32_t twist_table[8] = {
		0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
		0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278
	};

	for (; n--; buf++) {
		register u_int32_t w = roll(*buf, random_state.input_rotate);
		register u_int i = random_state.add_ptr =
		    (random_state.add_ptr - 1) & (POOLWORDS - 1);
		/*
		 * Normally, we add 7 bits of rotation to the pool.
		 * At the beginning of the pool, add an extra 7 bits
		 * rotation, so that successive passes spread the
		 * input bits across the pool evenly.
		 */
		random_state.input_rotate =
		    (random_state.input_rotate + (i? 7 : 14)) & 31;

		/* XOR in the various taps */
		w ^= random_state.pool[(i+TAP1) & (POOLWORDS-1)] ^
		     random_state.pool[(i+TAP2) & (POOLWORDS-1)] ^
		     random_state.pool[(i+TAP3) & (POOLWORDS-1)] ^
		     random_state.pool[(i+TAP4) & (POOLWORDS-1)] ^
		     random_state.pool[(i+TAP5) & (POOLWORDS-1)] ^
		     random_state.pool[i];
		random_state.pool[i] = (w >> 3) ^ twist_table[w & 7];
	}
}