1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// https://rust-lang.org/COPYRIGHT.
//
// 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-64 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, BlockRng64};
use prng::isaac_array::IsaacArray;

#[allow(non_camel_case_types)]
type w64 = w<u64>;

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

/// A random number generator that uses ISAAC-64, the 64-bit variant of 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].
///
/// ISAAC-64 is mostly similar to ISAAC. Because it operates on 64-bit integers
/// instead of 32-bit, it uses twice as much memory to hold its state and
/// results. Also it uses different constants for shifts and indirect indexing,
/// optimized to give good results for 64bit arithmetic.
///
/// ISAAC-64 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.
///
/// ## Overview of the ISAAC-64 algorithm:
/// (in pseudo-code)
///
/// ```text
/// Input: a, b, c, s[256] // state
/// Output: r[256] // results
///
/// mix(a,i) = !(a ^ a << 21)  if i = 0 mod 4
///              a ^ a >>  5   if i = 1 mod 4
///              a ^ a << 12   if i = 2 mod 4
///              a ^ a >> 33   if i = 3 mod 4
///
/// c = c + 1
/// b = b + c
///
/// for i in 0..256 {
///     x = s_[i]
///     a = mix(a,i) + s[i+128 mod 256]
///     y = a + b + s[x>>3 mod 256]
///     s[i] = y
///     b = x + s[y>>11 mod 256]
///     r[i] = b
/// }
/// ```
///
/// This implementation uses [`BlockRng64`] to implement the [`RngCore`] methods.
///
/// See for more information the documentation of [`IsaacRng`].
///
/// [^1]: Bob Jenkins, [*ISAAC and RC4*](
///       http://burtleburtle.net/bob/rand/isaac.html)
///
/// [`IsaacRng`]: ../isaac/struct.IsaacRng.html
/// [`Hc128Rng`]: ../hc128/struct.Hc128Rng.html
/// [`BlockRng64`]: ../../../rand_core/block/struct.BlockRng64.html
/// [`RngCore`]: ../../trait.RngCore.html
#[derive(Clone, Debug)]
#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
pub struct Isaac64Rng(BlockRng64<Isaac64Core>);

impl RngCore for Isaac64Rng {
    #[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 Isaac64Rng {
    type Seed = <Isaac64Core as SeedableRng>::Seed;

    fn from_seed(seed: Self::Seed) -> Self {
        Isaac64Rng(BlockRng64::<Isaac64Core>::from_seed(seed))
    }

    fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error> {
        BlockRng64::<Isaac64Core>::from_rng(rng).map(|rng| Isaac64Rng(rng))
    }
}

impl Isaac64Rng {
    /// Create a 64-bit ISAAC random number generator using the
    /// default fixed seed.
    ///
    /// DEPRECATED. `Isaac64Rng::new_from_u64(0)` will produce identical results.
    #[deprecated(since="0.5.0", note="use the FromEntropy or SeedableRng trait")]
    pub fn new_unseeded() -> Self {
        Self::new_from_u64(0)
    }

    /// Create an ISAAC-64 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.
    pub fn new_from_u64(seed: u64) -> Self {
        Isaac64Rng(BlockRng64::new(Isaac64Core::new_from_u64(seed)))
    }
}

/// The core of `Isaac64Rng`, used with `BlockRng`.
#[derive(Clone)]
#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
pub struct Isaac64Core {
    #[cfg_attr(feature="serde1",serde(with="super::isaac_array::isaac_array_serde"))]
    mem: [w64; RAND_SIZE],
    a: w64,
    b: w64,
    c: w64,
}

// Custom Debug implementation that does not expose the internal state
impl fmt::Debug for Isaac64Core {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Isaac64Core {{}}")
    }
}

impl BlockRngCore for Isaac64Core {
    type Item = u64;
    type Results = IsaacArray<Self::Item>;

    /// Refills the output buffer, `results`. See also the pseudocode desciption
    /// of the algorithm in the [`Isaac64Rng`] 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.
    /// 
    /// [`Isaac64Rng`]: struct.Isaac64Rng.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:&[w64; RAND_SIZE], v: w64, amount: usize) -> w64 {
            let index = (v >> amount).0 as usize % RAND_SIZE;
            mem[index]
        }

        #[inline]
        fn rngstep(mem: &mut [w64; RAND_SIZE],
                   results: &mut [u64; RAND_SIZE],
                   mix: w64,
                   a: &mut w64,
                   b: &mut w64,
                   base: usize,
                   m: usize,
                   m2: usize) {
            let x = mem[base + m];
            *a = mix + mem[base + m2];
            let y = *a + *b + ind(&mem, x, 3);
            mem[base + m] = y;
            *b = x + ind(&mem, y, 3 + 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 << 21)), &mut a, &mut b, i + 0, m, m2);
            rngstep(&mut self.mem, results,   a ^ (a >> 5 ),  &mut a, &mut b, i + 1, m, m2);
            rngstep(&mut self.mem, results,   a ^ (a << 12),  &mut a, &mut b, i + 2, m, m2);
            rngstep(&mut self.mem, results,   a ^ (a >> 33),  &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 << 21)), &mut a, &mut b, i + 0, m, m2);
            rngstep(&mut self.mem, results,   a ^ (a >> 5 ),  &mut a, &mut b, i + 1, m, m2);
            rngstep(&mut self.mem, results,   a ^ (a << 12),  &mut a, &mut b, i + 2, m, m2);
            rngstep(&mut self.mem, results,   a ^ (a >> 33),  &mut a, &mut b, i + 3, m, m2);
        }

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

impl Isaac64Core {
    /// Create a new ISAAC-64 random number generator.
    fn init(mut mem: [w64; RAND_SIZE], rounds: u32) -> Self {
        fn mix(a: &mut w64, b: &mut w64, c: &mut w64, d: &mut w64,
               e: &mut w64, f: &mut w64, g: &mut w64, h: &mut w64) {
            *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;
        }

        // These numbers are the result of initializing a...h with the
        // fractional part of the golden ratio in binary (0x9e3779b97f4a7c13)
        // and applying mix() 4 times.
        let mut a = w(0x647c4677a2884b7c);
        let mut b = w(0xb9f8b322c73ac862);
        let mut c = w(0x8c0ea5053d4712a0);
        let mut d = w(0xb29b2e824a595524);
        let mut e = w(0x82f053db8355e0ce);
        let mut f = w(0x48fe4a0fa5a09315);
        let mut g = w(0xae985bf2cbfc89ed);
        let mut h = w(0x98f5704f6c44c0ab);

        // 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) }
    }

    /// Create an ISAAC-64 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.
    pub fn new_from_u64(seed: u64) -> Self {
        let mut key = [w(0); RAND_SIZE];
        key[0] = w(seed);
        // 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)
    }
}

impl SeedableRng for Isaac64Core {
    type Seed = [u8; 32];

    fn from_seed(seed: Self::Seed) -> Self {
        let mut seed_u64 = [0u64; 4];
        le::read_u64_into(&seed, &mut seed_u64);
        // Convert the seed to `Wrapping<u64>` and zero-extend to `RAND_SIZE`.
        let mut seed_extended = [w(0); RAND_SIZE];
        for (x, y) in seed_extended.iter_mut().zip(seed_u64.iter()) {
            *x = w(*y);
        }
        Self::init(seed_extended, 2)
    }

    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(0u64); RAND_SIZE];
        unsafe {
            let ptr = seed.as_mut_ptr() as *mut u8;
            let slice = slice::from_raw_parts_mut(ptr, RAND_SIZE * 8);
            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 {RngCore, SeedableRng};
    use super::Isaac64Rng;

    #[test]
    fn test_isaac64_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 = Isaac64Rng::from_seed(seed);
        assert_eq!(rng1.next_u64(), 14964555543728284049);

        let mut rng2 = Isaac64Rng::from_rng(rng1).unwrap();
        assert_eq!(rng2.next_u64(), 919595328260451758);
    }

    #[test]
    fn test_isaac64_true_values_64() {
        let seed = [1,0,0,0, 0,0,0,0, 23,0,0,0, 0,0,0,0,
                    200,1,0,0, 0,0,0,0, 210,30,0,0, 0,0,0,0];
        let mut rng1 = Isaac64Rng::from_seed(seed);
        let mut results = [0u64; 10];
        for i in results.iter_mut() { *i = rng1.next_u64(); }
        let expected = [
                   15071495833797886820, 7720185633435529318,
                   10836773366498097981, 5414053799617603544,
                   12890513357046278984, 17001051845652595546,
                   9240803642279356310, 12558996012687158051,
                   14673053937227185542, 1677046725350116783];
        assert_eq!(results, expected);

        let seed = [57,48,0,0, 0,0,0,0, 50,9,1,0, 0,0,0,0,
                    49,212,0,0, 0,0,0,0, 148,38,0,0, 0,0,0,0];
        let mut rng2 = Isaac64Rng::from_seed(seed);
        // skip forward to the 10000th number
        for _ in 0..10000 { rng2.next_u64(); }

        for i in results.iter_mut() { *i = rng2.next_u64(); }
        let expected = [
            18143823860592706164, 8491801882678285927, 2699425367717515619,
            17196852593171130876, 2606123525235546165, 15790932315217671084,
            596345674630742204, 9947027391921273664, 11788097613744130851,
            10391409374914919106];
        assert_eq!(results, expected);
    }

    #[test]
    fn test_isaac64_true_values_32() {
        let seed = [1,0,0,0, 0,0,0,0, 23,0,0,0, 0,0,0,0,
                    200,1,0,0, 0,0,0,0, 210,30,0,0, 0,0,0,0];
        let mut rng = Isaac64Rng::from_seed(seed);
        let mut results = [0u32; 12];
        for i in results.iter_mut() { *i = rng.next_u32(); }
        // Subset of above values, as an LE u32 sequence
        let expected = [
                    3477963620, 3509106075,
                    687845478, 1797495790,
                    227048253, 2523132918,
                    4044335064, 1260557630,
                    4079741768, 3001306521,
                    69157722, 3958365844];
        assert_eq!(results, expected);
    }

    #[test]
    fn test_isaac64_true_values_mixed() {
        let seed = [1,0,0,0, 0,0,0,0, 23,0,0,0, 0,0,0,0,
                    200,1,0,0, 0,0,0,0, 210,30,0,0, 0,0,0,0];
        let mut rng = Isaac64Rng::from_seed(seed);
        // Test alternating between `next_u64` and `next_u32` works as expected.
        // Values are the same as `test_isaac64_true_values` and
        // `test_isaac64_true_values_32`.
        assert_eq!(rng.next_u64(), 15071495833797886820);
        assert_eq!(rng.next_u32(), 687845478);
        assert_eq!(rng.next_u32(), 1797495790);
        assert_eq!(rng.next_u64(), 10836773366498097981);
        assert_eq!(rng.next_u32(), 4044335064);
        // Skip one u32
        assert_eq!(rng.next_u64(), 12890513357046278984);
        assert_eq!(rng.next_u32(), 69157722);
    }

    #[test]
    fn test_isaac64_true_bytes() {
        let seed = [1,0,0,0, 0,0,0,0, 23,0,0,0, 0,0,0,0,
                    200,1,0,0, 0,0,0,0, 210,30,0,0, 0,0,0,0];
        let mut rng = Isaac64Rng::from_seed(seed);
        let mut results = [0u8; 32];
        rng.fill_bytes(&mut results);
        // Same as first values in test_isaac64_true_values as bytes in LE order
        let expected = [100, 131, 77, 207, 155, 181, 40, 209,
                        102, 176, 255, 40, 238, 155, 35, 107,
                        61, 123, 136, 13, 246, 243, 99, 150,
                        216, 167, 15, 241, 62, 149, 34, 75];
        assert_eq!(results, expected);
    }

    #[test]
    fn test_isaac64_new_uninitialized() {
        // Compare the results from initializing `IsaacRng` with
        // `new_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 = Isaac64Rng::new_from_u64(0);
        let mut results = [0u64; 16];
        for i in results.iter_mut() { *i = rng.next_u64(); }
        let expected: [u64; 16] = [
            0xF67DFBA498E4937C, 0x84A5066A9204F380, 0xFEE34BD5F5514DBB,
            0x4D1664739B8F80D6, 0x8607459AB52A14AA, 0x0E78BC5A98529E49,
            0xFE5332822AD13777, 0x556C27525E33D01A, 0x08643CA615F3149F,
            0xD0771FAF3CB04714, 0x30E86F68A37B008D, 0x3074EBC0488A3ADF,
            0x270645EA7A2790BC, 0x5601A0A8D3763C6A, 0x2F83071F53F325DD,
            0xB9090F3D42D2D2EA];
        assert_eq!(results, expected);
    }

    #[test]
    fn test_isaac64_clone() {
        let seed = [1,0,0,0, 0,0,0,0, 23,0,0,0, 0,0,0,0,
                    200,1,0,0, 0,0,0,0, 210,30,0,0, 0,0,0,0];
        let mut rng1 = Isaac64Rng::from_seed(seed);
        let mut rng2 = rng1.clone();
        for _ in 0..16 {
            assert_eq!(rng1.next_u64(), rng2.next_u64());
        }
    }

    #[test]
    #[cfg(all(feature="serde1", feature="std"))]
    fn test_isaac64_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 = Isaac64Rng::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: Isaac64Rng = bincode::deserialize_from(&mut read).expect("Could not deserialize");

        for _ in 0..300 { // more than the 256 buffered results
            assert_eq!(rng.next_u64(), deserialized.next_u64());
        }
    }
}