third_party/rust_crates/vendor/rand_isaac/src/isaac.rs - fuchsia - Git at Google

 // Copyright 2018 Developers of the Rand project.
 // Copyright 2013-2018 The Rust Project Developers.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or https://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 core::{fmt, slice};
 use core::num::Wrapping as w;
 use rand_core::{RngCore, SeedableRng, Error, le};
 use rand_core::block::{BlockRngCore, BlockRng};
 use isaac_array::IsaacArray;

 #[allow(non_camel_case_types)]
 type w32 = w<u32>;

 const RAND_SIZE_LEN: usize = 8;
 const RAND_SIZE: usize = 1 << RAND_SIZE_LEN;

 /// A random number generator that uses the ISAAC algorithm.
 ///
 /// ISAAC stands for "Indirection, Shift, Accumulate, Add, and Count" which are
 /// the principal bitwise operations employed. It is the most advanced of a
 /// series of array based random number generator designed by Robert Jenkins
 /// in 1996[^1][^2].
 ///
 /// ISAAC is notably fast and produces excellent quality random numbers for
 /// non-cryptographic applications.
 ///
 /// In spite of being designed with cryptographic security in mind, ISAAC hasn't
 /// been stringently cryptanalyzed and thus cryptographers do not not
 /// consensually trust it to be secure. When looking for a secure RNG, prefer
 /// [`Hc128Rng`] instead, which, like ISAAC, is an array-based RNG and one of
 /// the stream-ciphers selected the by eSTREAM contest.
 ///
 /// In 2006 an improvement to ISAAC was suggested by Jean-Philippe Aumasson,
 /// named ISAAC+[^3]. But because the specification is not complete, because
 /// there is no good implementation, and because the suggested bias may not
 /// exist, it is not implemented here.
 ///
 /// ## Overview of the ISAAC algorithm:
 /// (in pseudo-code)
 ///
 /// ```text
 /// Input: a, b, c, s[256] // state
 /// Output: r[256]         // results
 ///
 /// mix(a,i) = a ^ a << 13   if i = 0 mod 4
 ///            a ^ a >>  6   if i = 1 mod 4
 ///            a ^ a <<  2   if i = 2 mod 4
 ///            a ^ a >> 16   if i = 3 mod 4
 ///
 /// c = c + 1
 /// b = b + c
 ///
 /// for i in 0..256 {
 ///     x = s_[i]
 ///     a = f(a,i) + s[i+128 mod 256]
 ///     y = a + b + s[x>>2 mod 256]
 ///     s[i] = y
 ///     b = x + s[y>>10 mod 256]
 ///     r[i] = b
 /// }
 /// ```
 ///
 /// Numbers are generated in blocks of 256. This means the function above only
 /// runs once every 256 times you ask for a next random number. In all other
 /// circumstances the last element of the results array is returned.
 ///
 /// ISAAC therefore needs a lot of memory, relative to other non-crypto RNGs.
 /// 2 * 256 * 4 = 2 kb to hold the state and results.
 ///
 /// This implementation uses [`BlockRng`] to implement the [`RngCore`] methods.
 ///
 /// ## References
 /// [^1]: Bob Jenkins, [*ISAAC: A fast cryptographic random number generator*](
 ///       http://burtleburtle.net/bob/rand/isaacafa.html)
 ///
 /// [^2]: Bob Jenkins, [*ISAAC and RC4*](
 ///       http://burtleburtle.net/bob/rand/isaac.html)
 ///
 /// [^3]: Jean-Philippe Aumasson, [*On the pseudo-random generator ISAAC*](
 ///       https://eprint.iacr.org/2006/438)
 ///
 /// [`Hc128Rng`]: ../../rand_hc/struct.Hc128Rng.html
 /// [`BlockRng`]: ../../rand_core/block/struct.BlockRng.html
 /// [`RngCore`]: ../../rand_core/trait.RngCore.html
 #[derive(Clone, Debug)]
 #[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
 pub struct IsaacRng(BlockRng<IsaacCore>);

 impl RngCore for IsaacRng {
     #[inline(always)]
     fn next_u32(&mut self) -> u32 {
         self.0.next_u32()
     }

     #[inline(always)]
     fn next_u64(&mut self) -> u64 {
         self.0.next_u64()
     }

     fn fill_bytes(&mut self, dest: &mut [u8]) {
         self.0.fill_bytes(dest)
     }

     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
         self.0.try_fill_bytes(dest)
     }
 }

 impl SeedableRng for IsaacRng {
     type Seed = <IsaacCore as SeedableRng>::Seed;

     fn from_seed(seed: Self::Seed) -> Self {
         IsaacRng(BlockRng::<IsaacCore>::from_seed(seed))
     }

     /// Create an ISAAC random number generator using an `u64` as seed.
     /// If `seed == 0` this will produce the same stream of random numbers as
     /// the reference implementation when used unseeded.
     fn seed_from_u64(seed: u64) -> Self {
         IsaacRng(BlockRng::<IsaacCore>::seed_from_u64(seed))
     }

     fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error> {
         BlockRng::<IsaacCore>::from_rng(rng).map(|rng| IsaacRng(rng))
     }
 }

 impl IsaacRng {
     /// Create an ISAAC random number generator using an `u64` as seed.
     /// If `seed == 0` this will produce the same stream of random numbers as
     /// the reference implementation when used unseeded.
     #[deprecated(since="0.6.0", note="use SeedableRng::seed_from_u64 instead")]
     pub fn new_from_u64(seed: u64) -> Self {
         Self::seed_from_u64(seed)
     }
 }

 /// The core of `IsaacRng`, used with `BlockRng`.
 #[derive(Clone)]
 #[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
 pub struct IsaacCore {
     #[cfg_attr(feature="serde1",serde(with="super::isaac_array::isaac_array_serde"))]
     mem: [w32; RAND_SIZE],
     a: w32,
     b: w32,
     c: w32,
 }

 // Custom Debug implementation that does not expose the internal state
 impl fmt::Debug for IsaacCore {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "IsaacCore {{}}")
     }
 }

 impl BlockRngCore for IsaacCore {
     type Item = u32;
     type Results = IsaacArray<Self::Item>;

     /// Refills the output buffer, `results`. See also the pseudocode desciption
     /// of the algorithm in the [`IsaacRng`] documentation.
     ///
     /// Optimisations used (similar to the reference implementation):
     ///
     /// - The loop is unrolled 4 times, once for every constant of mix().
     /// - The contents of the main loop are moved to a function `rngstep`, to
     ///   reduce code duplication.
     /// - We use local variables for a and b, which helps with optimisations.
     /// - We split the main loop in two, one that operates over 0..128 and one
     ///   over 128..256. This way we can optimise out the addition and modulus
     ///   from `s[i+128 mod 256]`.
     /// - We maintain one index `i` and add `m` or `m2` as base (m2 for the
     ///   `s[i+128 mod 256]`), relying on the optimizer to turn it into pointer
     ///   arithmetic.
     /// - We fill `results` backwards. The reference implementation reads values
     ///   from `results` in reverse. We read them in the normal direction, to
     ///   make `fill_bytes` a memcopy. To maintain compatibility we fill in
     ///   reverse.
     ///
     /// [`IsaacRng`]: struct.IsaacRng.html
     fn generate(&mut self, results: &mut IsaacArray<Self::Item>) {
         self.c += w(1);
         // abbreviations
         let mut a = self.a;
         let mut b = self.b + self.c;
         const MIDPOINT: usize = RAND_SIZE / 2;

         #[inline]
         fn ind(mem:&[w32; RAND_SIZE], v: w32, amount: usize) -> w32 {
             let index = (v >> amount).0 as usize % RAND_SIZE;
             mem[index]
         }

         #[inline]
         fn rngstep(mem: &mut [w32; RAND_SIZE],
                    results: &mut [u32; RAND_SIZE],
                    mix: w32,
                    a: &mut w32,
                    b: &mut w32,
                    base: usize,
                    m: usize,
                    m2: usize) {
             let x = mem[base + m];
             *a = mix + mem[base + m2];
             let y = *a + *b + ind(&mem, x, 2);
             mem[base + m] = y;
             *b = x + ind(&mem, y, 2 + RAND_SIZE_LEN);
             results[RAND_SIZE - 1 - base - m] = (*b).0;
         }

         let mut m = 0;
         let mut m2 = MIDPOINT;
         for i in (0..MIDPOINT/4).map(|i| i * 4) {
             rngstep(&mut self.mem, results, a ^ (a << 13), &mut a, &mut b, i + 0, m, m2);
             rngstep(&mut self.mem, results, a ^ (a >> 6 ),  &mut a, &mut b, i + 1, m, m2);
             rngstep(&mut self.mem, results, a ^ (a << 2 ),  &mut a, &mut b, i + 2, m, m2);
             rngstep(&mut self.mem, results, a ^ (a >> 16),  &mut a, &mut b, i + 3, m, m2);
         }

         m = MIDPOINT;
         m2 = 0;
         for i in (0..MIDPOINT/4).map(|i| i * 4) {
             rngstep(&mut self.mem, results, a ^ (a << 13), &mut a, &mut b, i + 0, m, m2);
             rngstep(&mut self.mem, results, a ^ (a >> 6 ),  &mut a, &mut b, i + 1, m, m2);
             rngstep(&mut self.mem, results, a ^ (a << 2 ),  &mut a, &mut b, i + 2, m, m2);
             rngstep(&mut self.mem, results, a ^ (a >> 16),  &mut a, &mut b, i + 3, m, m2);
         }

         self.a = a;
         self.b = b;
     }
 }

 impl IsaacCore {
     /// Create a new ISAAC random number generator.
     ///
     /// The author Bob Jenkins describes how to best initialize ISAAC here:
     /// <https://rt.cpan.org/Public/Bug/Display.html?id=64324>
     /// The answer is included here just in case:
     ///
     /// "No, you don't need a full 8192 bits of seed data. Normal key sizes will
     /// do fine, and they should have their expected strength (eg a 40-bit key
     /// will take as much time to brute force as 40-bit keys usually will). You
     /// could fill the remainder with 0, but set the last array element to the
     /// length of the key provided (to distinguish keys that differ only by
     /// different amounts of 0 padding). You do still need to call `randinit()`
     /// to make sure the initial state isn't uniform-looking."
     /// "After publishing ISAAC, I wanted to limit the key to half the size of
     /// `r[]`, and repeat it twice. That would have made it hard to provide a
     /// key that sets the whole internal state to anything convenient. But I'd
     /// already published it."
     ///
     /// And his answer to the question "For my code, would repeating the key
     /// over and over to fill 256 integers be a better solution than
     /// zero-filling, or would they essentially be the same?":
     /// "If the seed is under 32 bytes, they're essentially the same, otherwise
     /// repeating the seed would be stronger. randinit() takes a chunk of 32
     /// bytes, mixes it, and combines that with the next 32 bytes, et cetera.
     /// Then loops over all the elements the same way a second time."
     #[inline]
     fn init(mut mem: [w32; RAND_SIZE], rounds: u32) -> Self {
         fn mix(a: &mut w32, b: &mut w32, c: &mut w32, d: &mut w32,
                e: &mut w32, f: &mut w32, g: &mut w32, h: &mut w32) {
             *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;
         }

         // These numbers are the result of initializing a...h with the
         // fractional part of the golden ratio in binary (0x9e3779b9)
         // and applying mix() 4 times.
         let mut a = w(0x1367df5a);
         let mut b = w(0x95d90059);
         let mut c = w(0xc3163e4b);
         let mut d = w(0x0f421ad8);
         let mut e = w(0xd92a4a78);
         let mut f = w(0xa51a3c49);
         let mut g = w(0xc4efea1b);
         let mut h = w(0x30609119);

         // Normally this should do two passes, to make all of the seed effect
         // all of `mem`
         for _ in 0..rounds {
             for i in (0..RAND_SIZE/8).map(|i| i * 8) {
                 a += mem[i  ]; b += mem[i+1];
                 c += mem[i+2]; d += mem[i+3];
                 e += mem[i+4]; f += mem[i+5];
                 g += mem[i+6]; h += mem[i+7];
                 mix(&mut a, &mut b, &mut c, &mut d,
                     &mut e, &mut f, &mut g, &mut h);
                 mem[i  ] = a; mem[i+1] = b;
                 mem[i+2] = c; mem[i+3] = d;
                 mem[i+4] = e; mem[i+5] = f;
                 mem[i+6] = g; mem[i+7] = h;
             }
         }

         Self { mem, a: w(0), b: w(0), c: w(0) }
     }
 }

 impl SeedableRng for IsaacCore {
     type Seed = [u8; 32];

     fn from_seed(seed: Self::Seed) -> Self {
         let mut seed_u32 = [0u32; 8];
         le::read_u32_into(&seed, &mut seed_u32);
         // Convert the seed to `Wrapping<u32>` and zero-extend to `RAND_SIZE`.
         let mut seed_extended = [w(0); RAND_SIZE];
         for (x, y) in seed_extended.iter_mut().zip(seed_u32.iter()) {
             *x = w(*y);
         }
         Self::init(seed_extended, 2)
     }

     /// Create an ISAAC random number generator using an `u64` as seed.
     /// If `seed == 0` this will produce the same stream of random numbers as
     /// the reference implementation when used unseeded.
     fn seed_from_u64(seed: u64) -> Self {
         let mut key = [w(0); RAND_SIZE];
         key[0] = w(seed as u32);
         key[1] = w((seed >> 32) as u32);
         // Initialize with only one pass.
         // A second pass does not improve the quality here, because all of the
         // seed was already available in the first round.
         // Not doing the second pass has the small advantage that if
         // `seed == 0` this method produces exactly the same state as the
         // reference implementation when used unseeded.
         Self::init(key, 1)
     }

     fn from_rng<R: RngCore>(mut rng: R) -> Result<Self, Error> {
         // Custom `from_rng` implementation that fills a seed with the same size
         // as the entire state.
         let mut seed = [w(0u32); RAND_SIZE];
         unsafe {
             let ptr = seed.as_mut_ptr() as *mut u8;

             let slice = slice::from_raw_parts_mut(ptr, RAND_SIZE * 4);
             rng.try_fill_bytes(slice)?;
         }
         for i in seed.iter_mut() {
             *i = w(i.0.to_le());
         }

         Ok(Self::init(seed, 2))
     }
 }

 #[cfg(test)]
 mod test {
     use rand_core::{RngCore, SeedableRng};
     use super::IsaacRng;

     #[test]
     fn test_isaac_construction() {
         // Test that various construction techniques produce a working RNG.
         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                     0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng1 = IsaacRng::from_seed(seed);
         assert_eq!(rng1.next_u32(), 2869442790);

         let mut rng2 = IsaacRng::from_rng(rng1).unwrap();
         assert_eq!(rng2.next_u32(), 3094074039);
     }

     #[test]
     fn test_isaac_true_values_32() {
         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                      57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng1 = IsaacRng::from_seed(seed);
         let mut results = [0u32; 10];
         for i in results.iter_mut() { *i = rng1.next_u32(); }
         let expected = [
             2558573138, 873787463, 263499565, 2103644246, 3595684709,
             4203127393, 264982119, 2765226902, 2737944514, 3900253796];
         assert_eq!(results, expected);

         let seed = [57,48,0,0, 50,9,1,0, 49,212,0,0, 148,38,0,0,
                     0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng2 = IsaacRng::from_seed(seed);
         // skip forward to the 10000th number
         for _ in 0..10000 { rng2.next_u32(); }

         for i in results.iter_mut() { *i = rng2.next_u32(); }
         let expected = [
             3676831399, 3183332890, 2834741178, 3854698763, 2717568474,
             1576568959, 3507990155, 179069555, 141456972, 2478885421];
         assert_eq!(results, expected);
     }

     #[test]
     fn test_isaac_true_values_64() {
         // As above, using little-endian versions of above values
         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                     57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng = IsaacRng::from_seed(seed);
         let mut results = [0u64; 5];
         for i in results.iter_mut() { *i = rng.next_u64(); }
         let expected = [
             3752888579798383186, 9035083239252078381,18052294697452424037,
             11876559110374379111, 16751462502657800130];
         assert_eq!(results, expected);
     }

     #[test]
     fn test_isaac_true_bytes() {
         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                      57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng = IsaacRng::from_seed(seed);
         let mut results = [0u8; 32];
         rng.fill_bytes(&mut results);
         // Same as first values in test_isaac_true_values as bytes in LE order
         let expected = [82, 186, 128, 152, 71, 240, 20, 52,
                         45, 175, 180, 15, 86, 16, 99, 125,
                         101, 203, 81, 214, 97, 162, 134, 250,
                         103, 78, 203, 15, 150, 3, 210, 164];
         assert_eq!(results, expected);
     }

     #[test]
     fn test_isaac_new_uninitialized() {
         // Compare the results from initializing `IsaacRng` with
         // `seed_from_u64(0)`, to make sure it is the same as the reference
         // implementation when used uninitialized.
         // Note: We only test the first 16 integers, not the full 256 of the
         // first block.
         let mut rng = IsaacRng::seed_from_u64(0);
         let mut results = [0u32; 16];
         for i in results.iter_mut() { *i = rng.next_u32(); }
         let expected: [u32; 16] = [
             0x71D71FD2, 0xB54ADAE7, 0xD4788559, 0xC36129FA,
             0x21DC1EA9, 0x3CB879CA, 0xD83B237F, 0xFA3CE5BD,
             0x8D048509, 0xD82E9489, 0xDB452848, 0xCA20E846,
             0x500F972E, 0x0EEFF940, 0x00D6B993, 0xBC12C17F];
         assert_eq!(results, expected);
     }

     #[test]
     fn test_isaac_clone() {
         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                      57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng1 = IsaacRng::from_seed(seed);
         let mut rng2 = rng1.clone();
         for _ in 0..16 {
             assert_eq!(rng1.next_u32(), rng2.next_u32());
         }
     }

     #[test]
     #[cfg(feature="serde1")]
     fn test_isaac_serde() {
         use bincode;
         use std::io::{BufWriter, BufReader};

         let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
                      57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
         let mut rng = IsaacRng::from_seed(seed);

         let buf: Vec<u8> = Vec::new();
         let mut buf = BufWriter::new(buf);
         bincode::serialize_into(&mut buf, &rng).expect("Could not serialize");

         let buf = buf.into_inner().unwrap();
         let mut read = BufReader::new(&buf[..]);
         let mut deserialized: IsaacRng = bincode::deserialize_from(&mut read).expect("Could not deserialize");

         for _ in 0..300 { // more than the 256 buffered results
             assert_eq!(rng.next_u32(), deserialized.next_u32());
         }
     }
 }
	// Copyright 2018 Developers of the Rand project.
	// Copyright 2013-2018 The Rust Project Developers.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or https://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 core::{fmt, slice};
	use core::num::Wrapping as w;
	use rand_core::{RngCore, SeedableRng, Error, le};
	use rand_core::block::{BlockRngCore, BlockRng};
	use isaac_array::IsaacArray;

	#[allow(non_camel_case_types)]
	type w32 = w<u32>;

	const RAND_SIZE_LEN: usize = 8;
	const RAND_SIZE: usize = 1 << RAND_SIZE_LEN;

	/// A random number generator that uses the ISAAC algorithm.
	///
	/// ISAAC stands for "Indirection, Shift, Accumulate, Add, and Count" which are
	/// the principal bitwise operations employed. It is the most advanced of a
	/// series of array based random number generator designed by Robert Jenkins
	/// in 1996[^1][^2].
	///
	/// ISAAC is notably fast and produces excellent quality random numbers for
	/// non-cryptographic applications.
	///
	/// In spite of being designed with cryptographic security in mind, ISAAC hasn't
	/// been stringently cryptanalyzed and thus cryptographers do not not
	/// consensually trust it to be secure. When looking for a secure RNG, prefer
	/// [`Hc128Rng`] instead, which, like ISAAC, is an array-based RNG and one of
	/// the stream-ciphers selected the by eSTREAM contest.
	///
	/// In 2006 an improvement to ISAAC was suggested by Jean-Philippe Aumasson,
	/// named ISAAC+[^3]. But because the specification is not complete, because
	/// there is no good implementation, and because the suggested bias may not
	/// exist, it is not implemented here.
	///
	/// ## Overview of the ISAAC algorithm:
	/// (in pseudo-code)
	///
	/// ```text
	/// Input: a, b, c, s[256] // state
	/// Output: r[256] // results
	///
	/// mix(a,i) = a ^ a << 13 if i = 0 mod 4
	/// a ^ a >> 6 if i = 1 mod 4
	/// a ^ a << 2 if i = 2 mod 4
	/// a ^ a >> 16 if i = 3 mod 4
	///
	/// c = c + 1
	/// b = b + c
	///
	/// for i in 0..256 {
	/// x = s_[i]
	/// a = f(a,i) + s[i+128 mod 256]
	/// y = a + b + s[x>>2 mod 256]
	/// s[i] = y
	/// b = x + s[y>>10 mod 256]
	/// r[i] = b
	/// }
	/// ```
	///
	/// Numbers are generated in blocks of 256. This means the function above only
	/// runs once every 256 times you ask for a next random number. In all other
	/// circumstances the last element of the results array is returned.
	///
	/// ISAAC therefore needs a lot of memory, relative to other non-crypto RNGs.
	/// 2 * 256 * 4 = 2 kb to hold the state and results.
	///
	/// This implementation uses [`BlockRng`] to implement the [`RngCore`] methods.
	///
	/// ## References
	/// [^1]: Bob Jenkins, [ISAAC: A fast cryptographic random number generator](
	/// http://burtleburtle.net/bob/rand/isaacafa.html)
	///
	/// [^2]: Bob Jenkins, [ISAAC and RC4](
	/// http://burtleburtle.net/bob/rand/isaac.html)
	///
	/// [^3]: Jean-Philippe Aumasson, [On the pseudo-random generator ISAAC](
	/// https://eprint.iacr.org/2006/438)
	///
	/// [`Hc128Rng`]: ../../rand_hc/struct.Hc128Rng.html
	/// [`BlockRng`]: ../../rand_core/block/struct.BlockRng.html
	/// [`RngCore`]: ../../rand_core/trait.RngCore.html
	#[derive(Clone, Debug)]
	#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
	pub struct IsaacRng(BlockRng<IsaacCore>);

	impl RngCore for IsaacRng {
	#[inline(always)]
	fn next_u32(&mut self) -> u32 {
	self.0.next_u32()
	}

	#[inline(always)]
	fn next_u64(&mut self) -> u64 {
	self.0.next_u64()
	}

	fn fill_bytes(&mut self, dest: &mut [u8]) {
	self.0.fill_bytes(dest)
	}

	fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
	self.0.try_fill_bytes(dest)
	}
	}

	impl SeedableRng for IsaacRng {
	type Seed = <IsaacCore as SeedableRng>::Seed;

	fn from_seed(seed: Self::Seed) -> Self {
	IsaacRng(BlockRng::<IsaacCore>::from_seed(seed))
	}

	/// Create an ISAAC random number generator using an `u64` as seed.
	/// If `seed == 0` this will produce the same stream of random numbers as
	/// the reference implementation when used unseeded.
	fn seed_from_u64(seed: u64) -> Self {
	IsaacRng(BlockRng::<IsaacCore>::seed_from_u64(seed))
	}

	fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error> {
	BlockRng::<IsaacCore>::from_rng(rng).map(\|rng\| IsaacRng(rng))
	}
	}

	impl IsaacRng {
	/// Create an ISAAC random number generator using an `u64` as seed.
	/// If `seed == 0` this will produce the same stream of random numbers as
	/// the reference implementation when used unseeded.
	#[deprecated(since="0.6.0", note="use SeedableRng::seed_from_u64 instead")]
	pub fn new_from_u64(seed: u64) -> Self {
	Self::seed_from_u64(seed)
	}
	}

	/// The core of `IsaacRng`, used with `BlockRng`.
	#[derive(Clone)]
	#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
	pub struct IsaacCore {
	#[cfg_attr(feature="serde1",serde(with="super::isaac_array::isaac_array_serde"))]
	mem: [w32; RAND_SIZE],
	a: w32,
	b: w32,
	c: w32,
	}

	// Custom Debug implementation that does not expose the internal state
	impl fmt::Debug for IsaacCore {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	write!(f, "IsaacCore {{}}")
	}
	}

	impl BlockRngCore for IsaacCore {
	type Item = u32;
	type Results = IsaacArray<Self::Item>;

	/// Refills the output buffer, `results`. See also the pseudocode desciption
	/// of the algorithm in the [`IsaacRng`] documentation.
	///
	/// Optimisations used (similar to the reference implementation):
	///
	/// - The loop is unrolled 4 times, once for every constant of mix().
	/// - The contents of the main loop are moved to a function `rngstep`, to
	/// reduce code duplication.
	/// - We use local variables for a and b, which helps with optimisations.
	/// - We split the main loop in two, one that operates over 0..128 and one
	/// over 128..256. This way we can optimise out the addition and modulus
	/// from `s[i+128 mod 256]`.
	/// - We maintain one index `i` and add `m` or `m2` as base (m2 for the
	/// `s[i+128 mod 256]`), relying on the optimizer to turn it into pointer
	/// arithmetic.
	/// - We fill `results` backwards. The reference implementation reads values
	/// from `results` in reverse. We read them in the normal direction, to
	/// make `fill_bytes` a memcopy. To maintain compatibility we fill in
	/// reverse.
	///
	/// [`IsaacRng`]: struct.IsaacRng.html
	fn generate(&mut self, results: &mut IsaacArray<Self::Item>) {
	self.c += w(1);
	// abbreviations
	let mut a = self.a;
	let mut b = self.b + self.c;
	const MIDPOINT: usize = RAND_SIZE / 2;

	#[inline]
	fn ind(mem:&[w32; RAND_SIZE], v: w32, amount: usize) -> w32 {
	let index = (v >> amount).0 as usize % RAND_SIZE;
	mem[index]
	}

	#[inline]
	fn rngstep(mem: &mut [w32; RAND_SIZE],
	results: &mut [u32; RAND_SIZE],
	mix: w32,
	a: &mut w32,
	b: &mut w32,
	base: usize,
	m: usize,
	m2: usize) {
	let x = mem[base + m];
	*a = mix + mem[base + m2];
	let y = a + b + ind(&mem, x, 2);
	mem[base + m] = y;
	*b = x + ind(&mem, y, 2 + RAND_SIZE_LEN);
	results[RAND_SIZE - 1 - base - m] = (*b).0;
	}

	let mut m = 0;
	let mut m2 = MIDPOINT;
	for i in (0..MIDPOINT/4).map(\|i\| i * 4) {
	rngstep(&mut self.mem, results, a ^ (a << 13), &mut a, &mut b, i + 0, m, m2);
	rngstep(&mut self.mem, results, a ^ (a >> 6 ), &mut a, &mut b, i + 1, m, m2);
	rngstep(&mut self.mem, results, a ^ (a << 2 ), &mut a, &mut b, i + 2, m, m2);
	rngstep(&mut self.mem, results, a ^ (a >> 16), &mut a, &mut b, i + 3, m, m2);
	}

	m = MIDPOINT;
	m2 = 0;
	for i in (0..MIDPOINT/4).map(\|i\| i * 4) {
	rngstep(&mut self.mem, results, a ^ (a << 13), &mut a, &mut b, i + 0, m, m2);
	rngstep(&mut self.mem, results, a ^ (a >> 6 ), &mut a, &mut b, i + 1, m, m2);
	rngstep(&mut self.mem, results, a ^ (a << 2 ), &mut a, &mut b, i + 2, m, m2);
	rngstep(&mut self.mem, results, a ^ (a >> 16), &mut a, &mut b, i + 3, m, m2);
	}

	self.a = a;
	self.b = b;
	}
	}

	impl IsaacCore {
	/// Create a new ISAAC random number generator.
	///
	/// The author Bob Jenkins describes how to best initialize ISAAC here:
	/// <https://rt.cpan.org/Public/Bug/Display.html?id=64324>
	/// The answer is included here just in case:
	///
	/// "No, you don't need a full 8192 bits of seed data. Normal key sizes will
	/// do fine, and they should have their expected strength (eg a 40-bit key
	/// will take as much time to brute force as 40-bit keys usually will). You
	/// could fill the remainder with 0, but set the last array element to the
	/// length of the key provided (to distinguish keys that differ only by
	/// different amounts of 0 padding). You do still need to call `randinit()`
	/// to make sure the initial state isn't uniform-looking."
	/// "After publishing ISAAC, I wanted to limit the key to half the size of
	/// `r[]`, and repeat it twice. That would have made it hard to provide a
	/// key that sets the whole internal state to anything convenient. But I'd
	/// already published it."
	///
	/// And his answer to the question "For my code, would repeating the key
	/// over and over to fill 256 integers be a better solution than
	/// zero-filling, or would they essentially be the same?":
	/// "If the seed is under 32 bytes, they're essentially the same, otherwise
	/// repeating the seed would be stronger. randinit() takes a chunk of 32
	/// bytes, mixes it, and combines that with the next 32 bytes, et cetera.
	/// Then loops over all the elements the same way a second time."
	#[inline]
	fn init(mut mem: [w32; RAND_SIZE], rounds: u32) -> Self {
	fn mix(a: &mut w32, b: &mut w32, c: &mut w32, d: &mut w32,
	e: &mut w32, f: &mut w32, g: &mut w32, h: &mut w32) {
	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;
	}

	// These numbers are the result of initializing a...h with the
	// fractional part of the golden ratio in binary (0x9e3779b9)
	// and applying mix() 4 times.
	let mut a = w(0x1367df5a);
	let mut b = w(0x95d90059);
	let mut c = w(0xc3163e4b);
	let mut d = w(0x0f421ad8);
	let mut e = w(0xd92a4a78);
	let mut f = w(0xa51a3c49);
	let mut g = w(0xc4efea1b);
	let mut h = w(0x30609119);

	// Normally this should do two passes, to make all of the seed effect
	// all of `mem`
	for _ in 0..rounds {
	for i in (0..RAND_SIZE/8).map(\|i\| i * 8) {
	a += mem[i ]; b += mem[i+1];
	c += mem[i+2]; d += mem[i+3];
	e += mem[i+4]; f += mem[i+5];
	g += mem[i+6]; h += mem[i+7];
	mix(&mut a, &mut b, &mut c, &mut d,
	&mut e, &mut f, &mut g, &mut h);
	mem[i ] = a; mem[i+1] = b;
	mem[i+2] = c; mem[i+3] = d;
	mem[i+4] = e; mem[i+5] = f;
	mem[i+6] = g; mem[i+7] = h;
	}
	}

	Self { mem, a: w(0), b: w(0), c: w(0) }
	}
	}

	impl SeedableRng for IsaacCore {
	type Seed = [u8; 32];

	fn from_seed(seed: Self::Seed) -> Self {
	let mut seed_u32 = [0u32; 8];
	le::read_u32_into(&seed, &mut seed_u32);
	// Convert the seed to `Wrapping<u32>` and zero-extend to `RAND_SIZE`.
	let mut seed_extended = [w(0); RAND_SIZE];
	for (x, y) in seed_extended.iter_mut().zip(seed_u32.iter()) {
	x = w(y);
	}
	Self::init(seed_extended, 2)
	}

	/// Create an ISAAC random number generator using an `u64` as seed.
	/// If `seed == 0` this will produce the same stream of random numbers as
	/// the reference implementation when used unseeded.
	fn seed_from_u64(seed: u64) -> Self {
	let mut key = [w(0); RAND_SIZE];
	key[0] = w(seed as u32);
	key[1] = w((seed >> 32) as u32);
	// Initialize with only one pass.
	// A second pass does not improve the quality here, because all of the
	// seed was already available in the first round.
	// Not doing the second pass has the small advantage that if
	// `seed == 0` this method produces exactly the same state as the
	// reference implementation when used unseeded.
	Self::init(key, 1)
	}

	fn from_rng<R: RngCore>(mut rng: R) -> Result<Self, Error> {
	// Custom `from_rng` implementation that fills a seed with the same size
	// as the entire state.
	let mut seed = [w(0u32); RAND_SIZE];
	unsafe {
	let ptr = seed.as_mut_ptr() as *mut u8;

	let slice = slice::from_raw_parts_mut(ptr, RAND_SIZE * 4);
	rng.try_fill_bytes(slice)?;
	}
	for i in seed.iter_mut() {
	*i = w(i.0.to_le());
	}

	Ok(Self::init(seed, 2))
	}
	}

	#[cfg(test)]
	mod test {
	use rand_core::{RngCore, SeedableRng};
	use super::IsaacRng;

	#[test]
	fn test_isaac_construction() {
	// Test that various construction techniques produce a working RNG.
	let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
	0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng1 = IsaacRng::from_seed(seed);
	assert_eq!(rng1.next_u32(), 2869442790);

	let mut rng2 = IsaacRng::from_rng(rng1).unwrap();
	assert_eq!(rng2.next_u32(), 3094074039);
	}

	#[test]
	fn test_isaac_true_values_32() {
	let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
	57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng1 = IsaacRng::from_seed(seed);
	let mut results = [0u32; 10];
	for i in results.iter_mut() { *i = rng1.next_u32(); }
	let expected = [
	2558573138, 873787463, 263499565, 2103644246, 3595684709,
	4203127393, 264982119, 2765226902, 2737944514, 3900253796];
	assert_eq!(results, expected);

	let seed = [57,48,0,0, 50,9,1,0, 49,212,0,0, 148,38,0,0,
	0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng2 = IsaacRng::from_seed(seed);
	// skip forward to the 10000th number
	for _ in 0..10000 { rng2.next_u32(); }

	for i in results.iter_mut() { *i = rng2.next_u32(); }
	let expected = [
	3676831399, 3183332890, 2834741178, 3854698763, 2717568474,
	1576568959, 3507990155, 179069555, 141456972, 2478885421];
	assert_eq!(results, expected);
	}

	#[test]
	fn test_isaac_true_values_64() {
	// As above, using little-endian versions of above values
	let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
	57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng = IsaacRng::from_seed(seed);
	let mut results = [0u64; 5];
	for i in results.iter_mut() { *i = rng.next_u64(); }
	let expected = [
	3752888579798383186, 9035083239252078381,18052294697452424037,
	11876559110374379111, 16751462502657800130];
	assert_eq!(results, expected);
	}

	#[test]
	fn test_isaac_true_bytes() {
	let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
	57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng = IsaacRng::from_seed(seed);
	let mut results = [0u8; 32];
	rng.fill_bytes(&mut results);
	// Same as first values in test_isaac_true_values as bytes in LE order
	let expected = [82, 186, 128, 152, 71, 240, 20, 52,
	45, 175, 180, 15, 86, 16, 99, 125,
	101, 203, 81, 214, 97, 162, 134, 250,
	103, 78, 203, 15, 150, 3, 210, 164];
	assert_eq!(results, expected);
	}

	#[test]
	fn test_isaac_new_uninitialized() {
	// Compare the results from initializing `IsaacRng` with
	// `seed_from_u64(0)`, to make sure it is the same as the reference
	// implementation when used uninitialized.
	// Note: We only test the first 16 integers, not the full 256 of the
	// first block.
	let mut rng = IsaacRng::seed_from_u64(0);
	let mut results = [0u32; 16];
	for i in results.iter_mut() { *i = rng.next_u32(); }
	let expected: [u32; 16] = [
	0x71D71FD2, 0xB54ADAE7, 0xD4788559, 0xC36129FA,
	0x21DC1EA9, 0x3CB879CA, 0xD83B237F, 0xFA3CE5BD,
	0x8D048509, 0xD82E9489, 0xDB452848, 0xCA20E846,
	0x500F972E, 0x0EEFF940, 0x00D6B993, 0xBC12C17F];
	assert_eq!(results, expected);
	}

	#[test]
	fn test_isaac_clone() {
	let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
	57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng1 = IsaacRng::from_seed(seed);
	let mut rng2 = rng1.clone();
	for _ in 0..16 {
	assert_eq!(rng1.next_u32(), rng2.next_u32());
	}
	}

	#[test]
	#[cfg(feature="serde1")]
	fn test_isaac_serde() {
	use bincode;
	use std::io::{BufWriter, BufReader};

	let seed = [1,0,0,0, 23,0,0,0, 200,1,0,0, 210,30,0,0,
	57,48,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0];
	let mut rng = IsaacRng::from_seed(seed);

	let buf: Vec<u8> = Vec::new();
	let mut buf = BufWriter::new(buf);
	bincode::serialize_into(&mut buf, &rng).expect("Could not serialize");

	let buf = buf.into_inner().unwrap();
	let mut read = BufReader::new(&buf[..]);
	let mut deserialized: IsaacRng = bincode::deserialize_from(&mut read).expect("Could not deserialize");

	for _ in 0..300 { // more than the 256 buffered results
	assert_eq!(rng.next_u32(), deserialized.next_u32());
	}
	}
	}