isaac 0.1.0

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! The ISAAC random number generator.

#![no_std]

extern crate random;

#[cfg(test)]
#[macro_use]
extern crate std;

use core::fmt;
use core::slice;
use core::iter::repeat;
use core::num::Wrapping as w;
use random::*;

type w32 = w<u32>;
type w64 = w<u64>;

const RAND_SIZE_64_LEN: usize = 8;
const RAND_SIZE_64: usize = 1 << RAND_SIZE_64_LEN;

/// A random number generator that uses ISAAC-64[1], the 64-bit
/// variant of the ISAAC algorithm.
///
/// The ISAAC algorithm is generally accepted as suitable for
/// cryptographic purposes, but this implementation has not be
/// verified as such. Prefer a generator like `OsRng` that defers to
/// the operating system for cases that need high security.
///
/// [1]: Bob Jenkins, [*ISAAC: A fast cryptographic random number
/// generator*](http://www.burtleburtle.net/bob/rand/isaacafa.html)
#[derive(Clone, Copy)]
pub struct Rng {
    cnt: usize,
    rsl: [w64; RAND_SIZE_64],
    mem: [w64; RAND_SIZE_64],
    a: w64,
    b: w64,
    c: w64,
}

impl fmt::Debug for Rng {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Rng")
         .field("cnt", &self.cnt)
         .field("rsl", &self.rsl.iter())
         .field("mem", &self.mem.iter())
         .field("a", &self.a)
         .field("b", &self.b)
         .field("c", &self.c)
         .finish()
    }
}

static empty: Rng = Rng {
    cnt: 0,
    rsl: [w(0); RAND_SIZE_64],
    mem: [w(0); RAND_SIZE_64],
    a: w(0),
    b: w(0),
    c: w(0),
};

impl Rng {
    /// Create a 64-bit ISAAC random number generator using the
    /// default fixed seed.
    pub fn new_unseeded() -> Rng {
        let mut rng = empty;
        rng.init(false);
        rng
    }

    /// Initializes `self`. If `use_rsl` is true, then use the current value
    /// of `rsl` as a seed, otherwise construct one algorithmically (not
    /// randomly).
    fn init(&mut self, use_rsl: bool) {
        macro_rules! init {
            ($var:ident) => (
                let mut $var = w(0x9e3779b97f4a7c13);
            )
        }
        init!(a);
        init!(b);
        init!(c);
        init!(d);
        init!(e);
        init!(f);
        init!(g);
        init!(h);

        macro_rules! mix {
            () => {{
                a = a - e;
                f = f ^ (h >> 9);
                h = h + a;

                b = b - f;
                g = g ^ (a << 9);
                a = a + b;

                c = c - g;
                h = h ^ (b >> 23);
                b = b + c;

                d = d - h;
                a = a ^ (c << 15);
                c = c + d;

                e = e - a;
                b = b ^ (d >> 14);
                d = d + e;

                f = f - b;
                c = c ^ (e << 20);
                e = e + f;

                g = g - c;
                d = d ^ (f >> 17);
                f = f + g;

                h = h - d;
                e = e ^ (g << 14);
                g = g + h;
            }}
        }

        for _ in 0..4 {
            mix!();
        }

        if use_rsl {
            macro_rules! memloop {
                ($arr:expr) => {{
                    for i in (0..RAND_SIZE_64 / 8).map(|i| i * 8) {
                        a = a + $arr[i];
                        b = b + $arr[i + 1];
                        c = c + $arr[i + 2];
                        d = d + $arr[i + 3];
                        e = e + $arr[i + 4];
                        f = f + $arr[i + 5];
                        g = g + $arr[i + 6];
                        h = h + $arr[i + 7];
                        mix!();
                        self.mem[i] = a;
                        self.mem[i + 1] = b;
                        self.mem[i + 2] = c;
                        self.mem[i + 3] = d;
                        self.mem[i + 4] = e;
                        self.mem[i + 5] = f;
                        self.mem[i + 6] = g;
                        self.mem[i + 7] = h;
                    }
                }}
            }

            memloop!(self.rsl);
            memloop!(self.mem);
        } else {
            for i in (0..RAND_SIZE_64 / 8).map(|i| i * 8) {
                mix!();
                self.mem[i] = a;
                self.mem[i + 1] = b;
                self.mem[i + 2] = c;
                self.mem[i + 3] = d;
                self.mem[i + 4] = e;
                self.mem[i + 5] = f;
                self.mem[i + 6] = g;
                self.mem[i + 7] = h;
            }
        }

        self.isaac64();
    }

    /// Refills the output buffer (`self.rsl`)
    fn isaac64(&mut self) {
        self.c = self.c + w(1);
        // abbreviations
        let mut a = self.a;
        let mut b = self.b + self.c;
        const MIDPOINT: usize = RAND_SIZE_64 / 2;
        const MP_VEC: [(usize, usize); 2] = [(0, MIDPOINT), (MIDPOINT, 0)];
        macro_rules! ind {
            ($x:expr) => {
                *self.mem.get_unchecked((($x >> 3).0 as usize) & (RAND_SIZE_64 - 1))
            }
        }

        for &(mr_offset, m2_offset) in &MP_VEC {
            for base in (0..MIDPOINT / 4).map(|i| i * 4) {

                macro_rules! rngstepp {
                    ($j:expr, $shift:expr) => {{
                        let base = base + $j;
                        let mix = a ^ (a << $shift);
                        let mix = if $j == 0 {!mix} else {mix};

                        unsafe {
                            let x = *self.mem.get_unchecked(base + mr_offset);
                            a = mix + *self.mem.get_unchecked(base + m2_offset);
                            let y = ind!(x) + a + b;
                            *self.mem.get_unchecked_mut(base + mr_offset) = y;

                            b = ind!(y >> RAND_SIZE_64_LEN) + x;
                            *self.rsl.get_unchecked_mut(base + mr_offset) = b;
                        }
                    }}
                }

                macro_rules! rngstepn {
                    ($j:expr, $shift:expr) => {{
                        let base = base + $j;
                        let mix = a ^ (a >> $shift);
                        let mix = if $j == 0 {!mix} else {mix};

                        unsafe {
                            let x = *self.mem.get_unchecked(base + mr_offset);
                            a = mix + *self.mem.get_unchecked(base + m2_offset);
                            let y = ind!(x) + a + b;
                            *self.mem.get_unchecked_mut(base + mr_offset) = y;

                            b = ind!(y >> RAND_SIZE_64_LEN) + x;
                            *self.rsl.get_unchecked_mut(base + mr_offset) = b;
                        }
                    }}
                }

                rngstepp!(0, 21);
                rngstepn!(1, 5);
                rngstepp!(2, 12);
                rngstepn!(3, 33);
            }
        }

        self.a = a;
        self.b = b;
        self.cnt = RAND_SIZE_64;
    }
}

impl RandomGen for Rng {
    // FIXME(https://github.com/rust-lang/rfcs/issues/628)
    // having gen_u32 like this should be unnecessary
    #[inline]
    fn gen_u32(&mut self) -> u32 {
        self.gen_u64() as u32
    }

    #[inline]
    fn gen_u64(&mut self) -> u64 {
        if self.cnt == 0 {
            // make some more numbers
            self.isaac64();
        }
        self.cnt -= 1;

        // See corresponding location in Rng.gen_u32 for
        // explanation.
        debug_assert!(self.cnt < RAND_SIZE_64);
        self.rsl[(self.cnt % RAND_SIZE_64) as usize].0
    }
}

impl<'a> Seedable<&'a [u64]> for Rng {
    fn reseed(&mut self, seed: &'a [u64]) {
        // make the seed into [seed[0], seed[1], ..., seed[seed.len()
        // - 1], 0, 0, ...], to fill rng.rsl.
        let seed_iter = seed.iter().cloned().chain(repeat(0));

        for (rsl_elem, seed_elem) in self.rsl.iter_mut().zip(seed_iter) {
            *rsl_elem = w(seed_elem);
        }
        self.cnt = 0;
        self.a = w(0);
        self.b = w(0);
        self.c = w(0);

        self.init(true);
    }

    /// Create an ISAAC random number generator with a seed. This can
    /// be any length, although the maximum number of elements used is
    /// 256 and any more will be silently ignored. A generator
    /// constructed with a given seed will generate the same sequence
    /// of values as all other generators constructed with that seed.
    fn from_seed(seed: &'a [u64]) -> Rng {
        let mut rng = empty;
        rng.reseed(seed);
        rng
    }
}

impl Random for Rng {
    fn random<G: ?Sized + RandomGen>(g: &mut G) -> Self {
        let mut ret = empty;
        unsafe {
            let ptr = ret.rsl.as_mut_ptr() as *mut u8;

            let slice = slice::from_raw_parts_mut(ptr, RAND_SIZE_64 * 8);
            g.fill_bytes(slice);
        }
        ret.cnt = 0;
        ret.a = w(0);
        ret.b = w(0);
        ret.c = w(0);

        ret.init(true);
        return ret;
    }
}


#[cfg(test)]
mod tests {
    use std::prelude::v1::*;

    use {RandomGen, Seedable, Stream};
    use super::Rng;

    #[test]
    fn test_rng_64_seeded() {
        let seed: &[_] = &[1, 23, 456, 7890, 12345];
        let ra: Rng = Seedable::from_seed(seed);
        let rb: Rng = Seedable::from_seed(seed);
        assert!(Iterator::eq(Stream::<_, u64>::new(ra).take(64),
                             Stream::<_, u64>::new(rb).take(64)));
    }

    #[test]
    fn test_rng_64_reseed() {
        let mut s = [0; 256];
        s[1] = 50;
        s[2] = 77;
        s[3] = 19;
        let mut r: Rng = Seedable::from_seed(&s[..]);
        let xs: Vec<u64> = Stream::new(&mut r).take(64).collect();

        r.reseed(&s);

        let ys: Vec<u64> = Stream::new(&mut r).take(64).collect();
        assert_eq!(xs, ys);
    }

    #[test]
    fn test_rng_64_true_values() {
        let seed: &[_] = &[1, 23, 456, 7890, 12345];
        let mut ra: Rng = Seedable::from_seed(seed);
        // Regression test that isaac is actually using the above vector
        let v = (0..10).map(|_| ra.gen_u64()).collect::<Vec<_>>();
        assert_eq!(v,
                   vec![547121783600835980, 14377643087320773276, 17351601304698403469,
                        1238879483818134882, 11952566807690396487, 13970131091560099343,
                        4469761996653280935, 15552757044682284409, 6860251611068737823,
                        13722198873481261842]);

        let seed: &[_] = &[12345, 67890, 54321, 9876];
        let mut rb: Rng = Seedable::from_seed(seed);
        // skip forward to the 10000th number
        for _ in 0..10000 {
            rb.gen_u64();
        }

        let v = (0..10).map(|_| rb.gen_u64()).collect::<Vec<_>>();
        assert_eq!(v,
                   vec![18143823860592706164, 8491801882678285927, 2699425367717515619,
                        17196852593171130876, 2606123525235546165, 15790932315217671084,
                        596345674630742204, 9947027391921273664, 11788097613744130851,
                        10391409374914919106]);

    }

    #[test]
    fn test_rng_clone() {
        let seed: &[_] = &[1, 23, 456, 7890, 12345];
        let mut rng: Rng = Seedable::from_seed(seed);
        let mut clone = rng.clone();
        for _ in 0..16 {
            assert_eq!(rng.gen_u64(), clone.gen_u64());
        }
    }
}