// Copyright (c) 2019-2022 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module musl

import rand.seed

// MuslRNG ported from https://git.musl-libc.org/cgit/musl/tree/src/prng/rand_r.c
pub struct MuslRNG {
mut:
	state u32 = seed.time_seed_32()
}

// seed sets the current random state based on `seed_data`.
// seed expects `seed_data` to be only one `u32`.
pub fn (mut rng MuslRNG) seed(seed_data []u32) {
	if seed_data.len != 1 {
		eprintln('MuslRNG needs only one unsigned 32-bit integer as a seed.')
		exit(1)
	}
	rng.state = seed_data[0]
}

// temper returns a tempered value based on `prev` value.
[inline]
fn temper(prev u32) u32 {
	mut x := prev
	x ^= x >> 11
	x ^= (x << 7) & 0x9D2C5680
	x ^= (x << 15) & 0xEFC60000
	x ^= (x >> 18)
	return x
}

// u32 returns a pseudorandom 32-bit unsigned integer (`u32`).
[inline]
pub fn (mut rng MuslRNG) u32() u32 {
	rng.state = rng.state * 1103515245 + 12345
	// We are not dividing by 2 (or shifting right by 1)
	// because we want all 32-bits of random data
	return temper(rng.state)
}

// u64 returns a pseudorandom 64-bit unsigned integer (`u64`).
[inline]
pub fn (mut rng MuslRNG) u64() u64 {
	return u64(rng.u32()) | (u64(rng.u32()) << 32)
}

// free should be called when the generator is no longer needed
[unsafe]
pub fn (mut rng MuslRNG) free() {
	unsafe { free(rng) }
}