/*
 * Copyright (c) 2026, Arm Limited. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 *
 */

#include <stdbool.h>
#include <string.h>

#include "sfcp_random.h"

struct xorshift_plus_128_state_t {
	uint64_t state[2];
};

static inline void lfsr_seed(struct xorshift_plus_128_state_t *lfsr,
			     uint8_t *seed, size_t seed_len)
{
	if (seed_len < sizeof(lfsr->state)) {
		memcpy(lfsr->state, seed, seed_len);
	} else {
		memcpy(lfsr->state, seed, sizeof(lfsr->state));
	}
}

/* See https://en.wikipedia.org/wiki/Xorshift#xorshift+ */
static uint64_t xorshift_plus_128_lfsr(struct xorshift_plus_128_state_t *lfsr,
				       uint8_t *seed, size_t seed_len)
{
	uint64_t temp0, temp1;

	lfsr_seed(lfsr, seed, seed_len);

	temp0 = lfsr->state[0];
	temp1 = lfsr->state[1];
	lfsr->state[0] = lfsr->state[1];

	temp0 ^= temp0 << 23;
	temp0 ^= temp0 >> 18;
	temp0 ^= temp1 ^ (temp1 >> 5);

	lfsr->state[1] = temp0;

	return temp0 + temp1;
}

uint64_t sfcp_random_generate_random_lfsr(uint8_t *seed, size_t seed_len)
{
	struct xorshift_plus_128_state_t lfsr = { 0 };

	return xorshift_plus_128_lfsr(&lfsr, seed, seed_len);
}