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// Copyright 2017 Steven Stewart-Gallus
//
// See the COPYRIGHT file at the top-level directory of this
// distribution.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied.  See the License for the specific language governing
// permissions and limitations under the License.
//
#![feature(thread_local)]
#![feature(asm)]
extern crate rand;

#[derive(Copy, Clone)]
struct Rng {
    init: bool,
    state: u64,
}

// Use MMIX RNG
#[thread_local]
static mut RNG: Rng = Rng {
    init: false,
    state: 0,
};

#[cold]
fn do_init() -> u64 {
    rand::random()
}

#[inline]
pub fn rand(min: u64, max: u64) -> u64 {
    unsafe {
        // __tls_get_addr once
        let rng = RNG;
        let mut init = rng.init;
        let mut state = rng.state;
        if !init {
            state = do_init();
            init = true;
        }
        let old = state;
        state = old.wrapping_mul(6364136223846793005).wrapping_add(1442695040888963407);

        let new = (old % (max.wrapping_add(1).wrapping_sub(min))).wrapping_add(min);

        // __tls_get_addr once again
        RNG = Rng {
            init: init,
            state: state,
        };

        return new;
    }
}