#include <linux/kernel.h>

enum poolinfo {
	POOL_WORDS = 128,
	POOL_WORDMASK = POOL_WORDS - 1,
	POOL_BITS = POOL_WORDS * sizeof(u32) * 8,
};

static u32 input_pool_data[POOL_WORDS];

static struct {
	u16 add_ptr;
} input_pool = { 0 };

void mix_tinylfsr(const void *in, int nbytes)
{
	unsigned long i = input_pool.add_ptr, next;
	const u8 *src = in;

	/* Mix one byte at a time to simplify size handling and churn faster. */
	while (nbytes--) {
		/* The simplest possible max period LFSR.
		 * This is morally equivalent to evaluating
		 * the input as a polynomial at x^32.
		 *
		 * It can be evaluated in parallel, since i+0
		 * only depends on i+0 and i+1. Thus i+0 depends
		 * on i+0,i+1, i+1 depends on i+1 and i+2,
		 * so we can absorb up to 126 bytes in parallel
		 * if necessary.
		 */
		next = (i + 1) & POOL_WORDMASK;
		input_pool_data[i] = *src++ ^ rol32(input_pool_data[i], 9) ^
				(input_pool_data[next] << 15) ^ (input_pool_data[next] >> 24);
		i = next;
	}
	input_pool.add_ptr = i;
}