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    // 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-64 random number generator.

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

    use {Rng, SeedableRng, Rand};

    #[allow(bad_style)]
    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(Copy)]
    pub struct Isaac64Rng {
        cnt: usize,
        rsl: [w64; RAND_SIZE_64],
        mem: [w64; RAND_SIZE_64],
        a: w64,
        b: w64,
        c: w64,
    }

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

    impl Isaac64Rng {
        /// 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 = 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 >> 3usize).0 as usize) & (RAND_SIZE_64 - 1))
                }
            }

            for &(mr_offset, m2_offset) in MP_VEC.iter() {
                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;
        }
    }

    // Cannot be derived because [u32; 256] does not implement Clone
    impl Clone for Isaac64Rng {
        fn clone(&self) -> Isaac64Rng {
            *self
        }
    }

    impl Rng for Isaac64Rng {
        #[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;

            // See corresponding location in IsaacRng.next_u32 for
            // explanation.
            debug_assert!(self.cnt < RAND_SIZE_64);
            self.rsl[(self.cnt % RAND_SIZE_64) as usize].0
        }
    }

    impl<'a> SeedableRng<&'a [u64]> for Isaac64Rng {
        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().map(|&x| x).chain(repeat(0u64));

            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]) -> Isaac64Rng {
            let mut rng = EMPTY_64;
            rng.reseed(seed);
            rng
        }
    }

    impl Rand for Isaac64Rng {
        fn rand<R: Rng>(other: &mut R) -> Isaac64Rng {
            let mut ret = EMPTY_64;
            unsafe {
                let ptr = ret.rsl.as_mut_ptr() as *mut u8;

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

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

    impl fmt::Debug for Isaac64Rng {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "Isaac64Rng {{}}")
        }
    }

    #[cfg(test)]
    mod test {
        use {Rng, SeedableRng};
        use super::Isaac64Rng;

        #[test]
        fn test_rng_64_rand_seeded() {
            let s = ::test::rng().gen_iter::<u64>().take(256).collect::<Vec<u64>>();
            let mut ra: Isaac64Rng = SeedableRng::from_seed(&s[..]);
            let mut rb: Isaac64Rng = SeedableRng::from_seed(&s[..]);
            assert!(::test::iter_eq(ra.gen_ascii_chars().take(100),
                                    rb.gen_ascii_chars().take(100)));
        }

        #[test]
        fn test_rng_64_seeded() {
            let seed: &[_] = &[1, 23, 456, 7890, 12345];
            let mut ra: Isaac64Rng = SeedableRng::from_seed(seed);
            let mut rb: Isaac64Rng = SeedableRng::from_seed(seed);
            assert!(::test::iter_eq(ra.gen_ascii_chars().take(100),
                                    rb.gen_ascii_chars().take(100)));
        }

        #[test]
        fn test_rng_64_reseed() {
            let s = ::test::rng().gen_iter::<u64>().take(256).collect::<Vec<u64>>();
            let mut r: Isaac64Rng = SeedableRng::from_seed(&s[..]);
            let string1: String = r.gen_ascii_chars().take(100).collect();

            r.reseed(&s[..]);

            let string2: String = r.gen_ascii_chars().take(100).collect();
            assert_eq!(string1, string2);
        }

        #[test]
        fn test_rng_64_true_values() {
            let seed: &[_] = &[1, 23, 456, 7890, 12345];
            let mut ra: Isaac64Rng = SeedableRng::from_seed(seed);
            // Regression test that isaac is actually using the above vector
            let v = (0..10).map(|_| ra.next_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: Isaac64Rng = SeedableRng::from_seed(seed);
            // skip forward to the 10000th number
            for _ in 0..10000 { rb.next_u64(); }

            let v = (0..10).map(|_| rb.next_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: Isaac64Rng = SeedableRng::from_seed(seed);
            let mut clone = rng.clone();
            for _ in 0..16 {
                assert_eq!(rng.next_u64(), clone.next_u64());
            }
        }
    }

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