// 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.

use cast;
use rand::{Rng, SeedableRng, OSRng};
use iter::{Iterator, range, range_step, Repeat};
use option::{None, Some};

static RAND_SIZE_LEN: u32 = 8;
static RAND_SIZE: u32 = 1 << RAND_SIZE_LEN;

/// A random number generator that uses the [ISAAC
/// algorithm](http://en.wikipedia.org/wiki/ISAAC_%28cipher%29).
///
/// The ISAAC algorithm is suitable for cryptographic purposes.
pub struct IsaacRng {
    priv cnt: u32,
    priv rsl: [u32, .. RAND_SIZE],
    priv mem: [u32, .. RAND_SIZE],
    priv a: u32,
    priv b: u32,
    priv c: u32
}
static EMPTY: IsaacRng = IsaacRng {
    cnt: 0,
    rsl: [0, .. RAND_SIZE],
    mem: [0, .. RAND_SIZE],
    a: 0, b: 0, c: 0
};

impl IsaacRng {
    /// Create an ISAAC random number generator with a random seed.
    pub fn new() -> IsaacRng {
        let mut rng = EMPTY;

        {
            let bytes = unsafe {cast::transmute::<&mut [u32], &mut [u8]>(rng.rsl)};
            OSRng::new().fill_bytes(bytes);
        }

        rng.init(true);
        rng
    }

    /// Create an ISAAC random number generator using the default
    /// fixed seed.
    pub fn new_unseeded() -> IsaacRng {
        let mut rng = EMPTY;
        rng.init(false);
        rng
    }

    /// Initialises `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) {
        let mut a = 0x9e3779b9;
        let mut b = a;
        let mut c = a;
        let mut d = a;
        let mut e = a;
        let mut f = a;
        let mut g = a;
        let mut h = a;

        macro_rules! mix(
            () => {{
                a^=b<<11; d+=a; b+=c;
                b^=c>>2;  e+=b; c+=d;
                c^=d<<8;  f+=c; d+=e;
                d^=e>>16; g+=d; e+=f;
                e^=f<<10; h+=e; f+=g;
                f^=g>>4;  a+=f; g+=h;
                g^=h<<8;  b+=g; h+=a;
                h^=a>>9;  c+=h; a+=b;
            }}
        );

        do 4.times { mix!(); }

        if use_rsl {
            macro_rules! memloop (
                ($arr:expr) => {{
                    for i in range_step(0u32, RAND_SIZE, 8) {
                        a+=$arr[i  ]; b+=$arr[i+1];
                        c+=$arr[i+2]; d+=$arr[i+3];
                        e+=$arr[i+4]; f+=$arr[i+5];
                        g+=$arr[i+6]; 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 range_step(0u32, RAND_SIZE, 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.isaac();
    }

    /// Refills the output buffer (`self.rsl`)
    #[inline]
    fn isaac(&mut self) {
        self.c += 1;
        // abbreviations
        let mut a = self.a;
        let mut b = self.b + self.c;

        static MIDPOINT: uint = RAND_SIZE as uint / 2;

        macro_rules! ind (($x:expr) => {
            self.mem[($x >> 2) & (RAND_SIZE - 1)]
        });
        macro_rules! rngstep(
            ($j:expr, $shift:expr) => {{
                let base = $j;
                let mix = if $shift < 0 {
                    a >> -$shift as uint
                } else {
                    a << $shift as uint
                };

                let x = self.mem[base  + mr_offset];
                a = (a ^ mix) + self.mem[base + m2_offset];
                let y = ind!(x) + a + b;
                self.mem[base + mr_offset] = y;

                b = ind!(y >> RAND_SIZE_LEN) + x;
                self.rsl[base + mr_offset] = b;
            }}
        );

        let r = [(0, MIDPOINT), (MIDPOINT, 0)];
        for &(mr_offset, m2_offset) in r.iter() {
            for i in range_step(0u, MIDPOINT, 4) {
                rngstep!(i + 0, 13);
                rngstep!(i + 1, -6);
                rngstep!(i + 2, 2);
                rngstep!(i + 3, -16);
            }
        }

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

impl Rng for IsaacRng {
    #[inline]
    fn next_u32(&mut self) -> u32 {
        if self.cnt == 0 {
            // make some more numbers
            self.isaac();
        }
        self.cnt -= 1;
        self.rsl[self.cnt]
    }
}

impl<'self> SeedableRng<&'self [u32]> for IsaacRng {
    fn reseed(&mut self, seed: &'self [u32]) {
        // make the seed into [seed[0], seed[1], ..., seed[seed.len()
        // - 1], 0, 0, ...], to fill rng.rsl.
        let seed_iter = seed.iter().map(|&x| x).chain(Repeat::new(0u32));

        for (rsl_elem, seed_elem) in self.rsl.mut_iter().zip(seed_iter) {
            *rsl_elem = seed_elem;
        }
        self.cnt = 0;
        self.a = 0;
        self.b = 0;
        self.c = 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: &'self [u32]) -> IsaacRng {
        let mut rng = EMPTY;
        rng.reseed(seed);
        rng
    }
}


static RAND_SIZE_64_LEN: uint = 8;
static RAND_SIZE_64: uint = 1 << RAND_SIZE_64_LEN;

/// A random number generator that uses the 64-bit variant of the
/// [ISAAC
/// algorithm](http://en.wikipedia.org/wiki/ISAAC_%28cipher%29).
///
/// The ISAAC algorithm is suitable for cryptographic purposes.
pub struct Isaac64Rng {
    priv cnt: uint,
    priv rsl: [u64, .. RAND_SIZE_64],
    priv mem: [u64, .. RAND_SIZE_64],
    priv a: u64,
    priv b: u64,
    priv c: u64,
}

static EMPTY_64: Isaac64Rng = Isaac64Rng {
    cnt: 0,
    rsl: [0, .. RAND_SIZE_64],
    mem: [0, .. RAND_SIZE_64],
    a: 0, b: 0, c: 0,
};

impl Isaac64Rng {
    /// Create a 64-bit ISAAC random number generator with a random
    /// seed.
    pub fn new() -> Isaac64Rng {
        let mut rng = EMPTY_64;
        {
            let bytes = unsafe {cast::transmute::<&mut [u64], &mut [u8]>(rng.rsl)};
            OSRng::new().fill_bytes(bytes);
        }
        rng.init(true);
        rng
    }

    /// Create a 64-bit ISAAC random number generator using the
    /// default fixed seed.
    pub fn new_unseeded() -> Isaac64Rng {
        let mut rng = EMPTY_64;
        rng.init(false);
        rng
    }

    /// Initialises `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 = 0x9e3779b97f4a7c13;
            )
        );
        init!(a); init!(b); init!(c); init!(d);
        init!(e); init!(f); init!(g); init!(h);

        macro_rules! mix(
            () => {{
                a-=e; f^=h>>9;  h+=a;
                b-=f; g^=a<<9;  a+=b;
                c-=g; h^=b>>23; b+=c;
                d-=h; a^=c<<15; c+=d;
                e-=a; b^=d>>14; d+=e;
                f-=b; c^=e<<20; e+=f;
                g-=c; d^=f>>17; f+=g;
                h-=d; e^=g<<14; g+=h;
            }}
        );

        for _ in range(0, 4) { mix!(); }
        if use_rsl {
            macro_rules! memloop (
                ($arr:expr) => {{
                    for i in range(0, RAND_SIZE_64 / 8).map(|i| i * 8) {
                        a+=$arr[i  ]; b+=$arr[i+1];
                        c+=$arr[i+2]; d+=$arr[i+3];
                        e+=$arr[i+4]; f+=$arr[i+5];
                        g+=$arr[i+6]; 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 range(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 += 1;
        // abbreviations
        let mut a = self.a;
        let mut b = self.b + self.c;
        static MIDPOINT: uint =  RAND_SIZE_64 / 2;
        static MP_VEC: [(uint, uint), .. 2] = [(0,MIDPOINT), (MIDPOINT, 0)];
        macro_rules! ind (
            ($x:expr) => {
                self.mem.unsafe_get(($x as uint >> 3) & (RAND_SIZE_64 - 1))
            }
        );
        macro_rules! rngstep(
            ($j:expr, $shift:expr) => {{
                let base = base + $j;
                let mix = a ^ (if $shift < 0 {
                    a >> -$shift as uint
                } else {
                    a << $shift as uint
                });
                let mix = if $j == 0 {!mix} else {mix};

                unsafe {
                    let x = self.mem.unsafe_get(base + mr_offset);
                    a = mix + self.mem.unsafe_get(base + m2_offset);
                    let y = ind!(x) + a + b;
                    self.mem.unsafe_set(base + mr_offset, y);

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

        for &(mr_offset, m2_offset) in MP_VEC.iter() {
            for base in range(0, MIDPOINT / 4).map(|i| i * 4) {
                rngstep!(0, 21);
                rngstep!(1, -5);
                rngstep!(2, 12);
                rngstep!(3, -33);
            }
        }

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

impl Rng for Isaac64Rng {
    // FIXME #7771: having next_u32 like this should be unnecessary
    #[inline]
    fn next_u32(&mut self) -> u32 {
        self.next_u64() as u32
    }

    #[inline]
    fn next_u64(&mut self) -> u64 {
        if self.cnt == 0 {
            // make some more numbers
            self.isaac64();
        }
        self.cnt -= 1;
        unsafe { self.rsl.unsafe_get(self.cnt) }
    }
}

impl<'self> SeedableRng<&'self [u64]> for Isaac64Rng {
    fn reseed(&mut self, seed: &'self [u64]) {
        // make the seed into [seed[0], seed[1], ..., seed[seed.len()
        // - 1], 0, 0, ...], to fill rng.rsl.
        let seed_iter = seed.iter().map(|&x| x).chain(Repeat::new(0u64));

        for (rsl_elem, seed_elem) in self.rsl.mut_iter().zip(seed_iter) {
            *rsl_elem = seed_elem;
        }
        self.cnt = 0;
        self.a = 0;
        self.b = 0;
        self.c = 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: &'self [u64]) -> Isaac64Rng {
        let mut rng = EMPTY_64;
        rng.reseed(seed);
        rng
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use rand::{Rng, SeedableRng, OSRng};
    use option::Some;
    use iter::range;
    use vec;

    #[test]
    fn test_rng_32_rand_seeded() {
        let s = OSRng::new().gen_vec::<u32>(256);
        let mut ra: IsaacRng = SeedableRng::from_seed(s.as_slice());
        let mut rb: IsaacRng = SeedableRng::from_seed(s.as_slice());
        assert_eq!(ra.gen_ascii_str(100u), rb.gen_ascii_str(100u));
    }
    #[test]
    fn test_rng_64_rand_seeded() {
        let s = OSRng::new().gen_vec::<u64>(256);
        let mut ra: Isaac64Rng = SeedableRng::from_seed(s.as_slice());
        let mut rb: Isaac64Rng = SeedableRng::from_seed(s.as_slice());
        assert_eq!(ra.gen_ascii_str(100u), rb.gen_ascii_str(100u));
    }

    #[test]
    fn test_rng_32_seeded() {
        let seed = &[2, 32, 4, 32, 51];
        let mut ra: IsaacRng = SeedableRng::from_seed(seed);
        let mut rb: IsaacRng = SeedableRng::from_seed(seed);
        assert_eq!(ra.gen_ascii_str(100u), rb.gen_ascii_str(100u));
    }
    #[test]
    fn test_rng_64_seeded() {
        let seed = &[2, 32, 4, 32, 51];
        let mut ra: Isaac64Rng = SeedableRng::from_seed(seed);
        let mut rb: Isaac64Rng = SeedableRng::from_seed(seed);
        assert_eq!(ra.gen_ascii_str(100u), rb.gen_ascii_str(100u));
    }

    #[test]
    fn test_rng_32_reseed() {
        let s = OSRng::new().gen_vec::<u32>(256);
        let mut r: IsaacRng = SeedableRng::from_seed(s.as_slice());
        let string1 = r.gen_ascii_str(100);

        r.reseed(s);

        let string2 = r.gen_ascii_str(100);
        assert_eq!(string1, string2);
    }
    #[test]
    fn test_rng_64_reseed() {
        let s = OSRng::new().gen_vec::<u64>(256);
        let mut r: Isaac64Rng = SeedableRng::from_seed(s.as_slice());
        let string1 = r.gen_ascii_str(100);

        r.reseed(s);

        let string2 = r.gen_ascii_str(100);
        assert_eq!(string1, string2);
    }

    #[test]
    fn test_rng_32_true_values() {
        let seed = &[2, 32, 4, 32, 51];
        let mut ra: IsaacRng = SeedableRng::from_seed(seed);
        // Regression test that isaac is actually using the above vector
        let v = vec::from_fn(10, |_| ra.next_u32());
        assert_eq!(v,
                   ~[447462228, 2081944040, 3163797308, 2379916134, 2377489184,
                     1132373754, 536342443, 2995223415, 1265094839, 345325140]);

        let seed = &[500, -4000, 123456, 9876543, 1, 1, 1, 1, 1];
        let mut rb: IsaacRng = SeedableRng::from_seed(seed);
        // skip forward to the 10000th number
        for _ in range(0, 10000) { rb.next_u32(); }

        let v = vec::from_fn(10, |_| rb.next_u32());
        assert_eq!(v,
                   ~[612373032, 292987903, 1819311337, 3141271980, 422447569,
                     310096395, 1083172510, 867909094, 2478664230, 2073577855]);
    }
    #[test]
    fn test_rng_64_true_values() {
        let seed = &[2, 32, 4, 32, 51];
        let mut ra: Isaac64Rng = SeedableRng::from_seed(seed);
        // Regression test that isaac is actually using the above vector
        let v = vec::from_fn(10, |_| ra.next_u64());
        assert_eq!(v,
                   ~[15015576812873463115, 12461067598045625862, 14818626436142668771,
                     5562406406765984441, 11813289907965514161, 13443797187798420053,
                     6935026941854944442, 7750800609318664042, 14428747036317928637,
                     14028894460301215947]);

        let seed = &[500, -4000, 123456, 9876543, 1, 1, 1, 1, 1];
        let mut rb: Isaac64Rng = SeedableRng::from_seed(seed);
        // skip forward to the 10000th number
        for _ in range(0, 10000) { rb.next_u64(); }

        let v = vec::from_fn(10, |_| rb.next_u64());
        assert_eq!(v,
                   ~[13557216323596688637, 17060829581390442094, 4927582063811333743,
                     2699639759356482270, 4819341314392384881, 6047100822963614452,
                     11086255989965979163, 11901890363215659856, 5370800226050011580,
                     16496463556025356451]);
    }
}