/*	$NetBSD: xoshiro128starstar.c,v 1.1 2024/02/18 20:57:51 christos Exp $	*/

/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0.  If a copy of the MPL was not distributed with this
 * file, you can obtain one at https://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

/*
 * Written in 2018 by David Blackman and Sebastiano Vigna (vigna@acm.org)
 *
 * To the extent possible under law, the author has dedicated all
 * copyright and related and neighboring rights to this software to the
 * public domain worldwide. This software is distributed without any
 * warranty.
 *
 * See <http://creativecommons.org/publicdomain/zero/1.0/>.
 */

#include <inttypes.h>

#include <isc/thread.h>

/*
 * This is xoshiro128** 1.0, our 32-bit all-purpose, rock-solid generator.
 * It has excellent (sub-ns) speed, a state size (128 bits) that is large
 * enough for mild parallelism, and it passes all tests we are aware of.
 *
 * For generating just single-precision (i.e., 32-bit) floating-point
 * numbers, xoshiro128+ is even faster.
 *
 * The state must be seeded so that it is not everywhere zero.
 */
ISC_THREAD_LOCAL uint32_t seed[4] = { 0 };

static uint32_t
rotl(const uint32_t x, int k) {
	return ((x << k) | (x >> (32 - k)));
}

static uint32_t
next(void) {
	uint32_t result_starstar, t;

	result_starstar = rotl(seed[0] * 5, 7) * 9;
	t = seed[1] << 9;

	seed[2] ^= seed[0];
	seed[3] ^= seed[1];
	seed[1] ^= seed[2];
	seed[0] ^= seed[3];

	seed[2] ^= t;

	seed[3] = rotl(seed[3], 11);

	return (result_starstar);
}