alazar 0.0.2

randomness
Documentation 
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

// alazar::xorshift::u128
//
//! 128-bit versions of XorShift generators.
//

use devela::convert::{
    u128_into_u32_le, u128_into_u64_le, u32_from_u16_le, u32_from_u8_le, u64_from_u16_le,
    u64_from_u32_le, u64_from_u8_le, u64_into_u32_le,
};

/// The `XorShift128` pseudo-random number generator.
///
/// It has a 128-bit state and generates 64-bit numbers.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct XorShift128([u32; 4]);

impl Default for XorShift128 {
    fn default() -> Self {
        Self::new_unchecked(Self::DEFAULT_SEED)
    }
}

// private associated items
impl XorShift128 {
    const DEFAULT_SEED: [u32; 4] = [0xDEFA0017; 4];

    #[cold]
    #[inline]
    const fn cold_path_result() -> Option<Self> {
        None
    }

    #[cold]
    #[inline]
    #[allow(dead_code)]
    const fn cold_path_default() -> Self {
        Self::new_unchecked(Self::DEFAULT_SEED)
    }
}

impl XorShift128 {
    /// Returns a seeded `XorShift128` generator from the given 4 × 32-bit seeds.
    ///
    /// Returns `None` if all given seeds are `0`.
    #[inline]
    #[must_use]
    pub const fn new(seeds: [u32; 4]) -> Option<Self> {
        if (seeds[0] | seeds[1] | seeds[2] | seeds[3]) == 0 {
            Self::cold_path_result()
        } else {
            Some(Self([seeds[0], seeds[1], seeds[2], seeds[3]]))
        }
    }

    /// Returns a seeded `XorShift128` generator from the given 8-bit seed,
    /// unchecked.
    ///
    /// The seeds must not be all `0`, otherwise every result will also be `0`.
    ///
    /// # Panics
    /// Panics in debug if the seeds are all `0`.
    #[inline]
    #[must_use]
    pub const fn new_unchecked(seeds: [u32; 4]) -> Self {
        debug_assert![
            (seeds[0] | seeds[1] | seeds[2] | seeds[3]) != 0,
            "Seeds must be non-zero"
        ];
        Self(seeds)
    }

    /// Returns the current random `u64`.
    #[inline(always)]
    #[must_use]
    pub const fn current_u64(&self) -> u64 {
        ((self.0[0] as u64) << 32) | (self.0[1] as u64)
    }

    /// Returns the next random `u64`.
    #[inline]
    #[must_use]
    pub fn next_u64(&mut self) -> u64 {
        let t = self.0[3];
        let mut s = self.0[0];
        self.0[3] = self.0[2];
        self.0[2] = self.0[1];
        self.0[1] = s;
        s ^= s << 11;
        s ^= s >> 8;
        self.0[0] = s ^ t ^ (t >> 19);

        ((self.0[0] as u64) << 32) | (self.0[1] as u64)
    }

    /// Returns a copy of the next new random state.
    #[inline]
    #[must_use]
    pub const fn next_new(&self) -> Self {
        let mut x = self.0;

        let t = x[3];
        let mut s = x[0];
        x[3] = x[2];
        x[2] = x[1];
        x[1] = s;
        s ^= s << 11;
        s ^= s >> 8;
        x[0] = s ^ t ^ (t >> 19);

        Self(x)
    }
}

/// # Extra constructors
impl XorShift128 {
    /// Returns a seeded `XorShift128` generator from the given 128-bit seed.
    ///
    /// The seeds will be split in little endian order.
    #[inline]
    pub const fn new1_u128(seed: u128) -> Option<Self> {
        Self::new(u128_into_u32_le(seed))
    }

    /// Returns a seeded `XorShift128` generator from the given 2 × 64-bit seeds.
    ///
    /// The seeds will be split in little endian order.
    #[inline]
    pub const fn new2_u64(seeds: [u64; 2]) -> Option<Self> {
        let [x, y] = u64_into_u32_le(seeds[0]);
        let [z, a] = u64_into_u32_le(seeds[1]);
        Self::new([x, y, z, a])
    }

    /// Returns a seeded `XorShift128` generator from the given 4 × 32-bit seeds.
    ///
    /// This is an alias of [`new`][Self#method.new].
    #[inline]
    pub const fn new4_u32(seeds: [u32; 4]) -> Option<Self> {
        Self::new(seeds)
    }

    /// Returns a seeded `XorShift128` generator from the given 8 × 16-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[inline]
    pub const fn new8_u16(seeds: [u16; 8]) -> Option<Self> {
        Self::new([
            u32_from_u16_le([seeds[0], seeds[1]]),
            u32_from_u16_le([seeds[2], seeds[3]]),
            u32_from_u16_le([seeds[4], seeds[5]]),
            u32_from_u16_le([seeds[6], seeds[7]]),
        ])
    }

    /// Returns a seeded `XorShift128` generator from the given 16 × 8-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[inline]
    pub const fn new16_u8(seeds: [u8; 16]) -> Option<Self> {
        Self::new([
            u32_from_u8_le([seeds[0], seeds[1], seeds[2], seeds[3]]),
            u32_from_u8_le([seeds[4], seeds[5], seeds[6], seeds[7]]),
            u32_from_u8_le([seeds[8], seeds[9], seeds[10], seeds[11]]),
            u32_from_u8_le([seeds[12], seeds[13], seeds[14], seeds[15]]),
        ])
    }
}

/// The `XorShift128+` pseudo-random number generator.
///
/// It has a 128-bit state and generates 64-bit numbers.
///
/// It is generally considered to have better statistical properties than
/// [`XorShift128`].
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct XorShift128p([u64; 2]);

impl Default for XorShift128p {
    fn default() -> Self {
        Self::new_unchecked([0xDEFA0017_DEFA0017; 2])
    }
}

// private associated items
impl XorShift128p {
    const DEFAULT_SEED: [u64; 2] = [0xDEFA0017_DEFA0017; 2];

    #[cold]
    #[inline]
    const fn cold_path_result() -> Option<Self> {
        None
    }

    #[cold]
    #[inline]
    #[allow(dead_code)]
    const fn cold_path_default() -> Self {
        Self::new_unchecked(Self::DEFAULT_SEED)
    }
}

impl XorShift128p {
    /// Returns a seeded `XorShift128+` generator from the given 2 × 64-bit seeds.
    ///
    /// Returns `None` if all given seeds are `0`.
    #[inline]
    #[must_use]
    pub const fn new(seeds: [u64; 2]) -> Option<Self> {
        if (seeds[0] | seeds[1]) == 0 {
            Self::cold_path_result()
        } else {
            Some(Self(seeds))
        }
    }

    /// Returns a seeded `XorShift128p` generator from the given 8-bit seed,
    /// unchecked.
    ///
    /// The seeds must not be all `0`, otherwise every result will also be `0`.
    ///
    /// # Panics
    /// Panics in debug if the seeds are all `0`.
    #[inline]
    #[must_use]
    pub const fn new_unchecked(seeds: [u64; 2]) -> Self {
        debug_assert![(seeds[0] | seeds[1]) != 0, "Seeds must be non-zero"];
        Self(seeds)
    }

    /// Returns the current random `u64`.
    #[inline(always)]
    #[must_use]
    pub const fn current_u64(&self) -> u64 {
        self.0[0].wrapping_add(self.0[1])
    }

    /// Returns the next random `u64`.
    #[inline]
    #[must_use]
    pub fn next_u64(&mut self) -> u64 {
        let [s0, mut s1] = [self.0[0], self.0[1]];
        let result = s0.wrapping_add(s1);

        s1 ^= s0;
        self.0[0] = s0.rotate_left(55) ^ s1 ^ (s1 << 14); // a, b
        self.0[1] = s1.rotate_left(36); // c

        result
    }

    /// Returns a copy of the next new random state.
    #[inline]
    #[must_use]
    pub const fn next_new(&self) -> Self {
        let mut x = self.0;
        let [s0, mut s1] = [x[0], x[1]];

        s1 ^= s0;
        x[0] = s0.rotate_left(55) ^ s1 ^ (s1 << 14); // a, b
        x[1] = s1.rotate_left(36); // c

        Self(x)
    }
}

/// # Extra constructors
impl XorShift128p {
    /// Returns a seeded `XorShift128+` generator from the given 128-bit seed.
    ///
    /// The seeds will be split in little endian order.
    #[inline]
    pub const fn new1_u128(seed: u128) -> Option<Self> {
        Self::new(u128_into_u64_le(seed))
    }

    /// Returns a seeded `XorShift128+` generator from the given 2 × 64-bit seeds.
    ///
    /// This is an alias of [`new`][Self#method.new].
    #[inline]
    pub const fn new2_u64(seeds: [u64; 2]) -> Option<Self> {
        Self::new(seeds)
    }

    /// Returns a seeded `XorShift128+` generator from the given 4 × 32-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[inline]
    pub const fn new4_u32(seeds: [u32; 4]) -> Option<Self> {
        Self::new([
            u64_from_u32_le([seeds[0], seeds[1]]),
            u64_from_u32_le([seeds[2], seeds[3]]),
        ])
    }

    /// Returns a seeded `XorShift128+` generator from the given 8 × 16-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[inline]
    pub const fn new8_u16(seeds: [u16; 8]) -> Option<Self> {
        Self::new([
            u64_from_u16_le([seeds[0], seeds[1], seeds[2], seeds[3]]),
            u64_from_u16_le([seeds[4], seeds[5], seeds[6], seeds[7]]),
        ])
    }

    /// Returns a seeded `XorShift128` generator from the given 4 × 8-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[inline]
    pub const fn new16_u8(seeds: [u8; 16]) -> Option<Self> {
        let s = seeds;
        Self::new([
            u64_from_u8_le([s[0], s[1], s[2], s[3], s[4], s[5], s[6], s[7]]),
            u64_from_u8_le([s[8], s[9], s[10], s[11], s[12], s[13], s[14], s[15]]),
        ])
    }
}

#[cfg(feature = "rand_core")]
#[cfg_attr(feature = "nightly", doc(cfg(feature = "rand_core")))]
mod impl_rand {
    use super::{XorShift128, XorShift128p};
    use rand_core::{Error, RngCore, SeedableRng};

    impl RngCore for XorShift128 {
        /// Returns the next random `u32`,
        /// from the first 32-bits of `next_u64`.
        fn next_u32(&mut self) -> u32 {
            (self.next_u64() & 0xFFFF_FFFF) as u32
        }

        /// Returns the next random `u64`.
        fn next_u64(&mut self) -> u64 {
            self.next_u64()
        }

        fn fill_bytes(&mut self, dest: &mut [u8]) {
            let mut i = 0;
            while i < dest.len() {
                let random_u64 = self.next_u64();
                let bytes = random_u64.to_le_bytes();
                let remaining = dest.len() - i;

                if remaining >= 8 {
                    dest[i..i + 8].copy_from_slice(&bytes);
                    i += 8;
                } else {
                    dest[i..].copy_from_slice(&bytes[..remaining]);
                    break;
                }
            }
        }

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

    impl SeedableRng for XorShift128 {
        type Seed = [u8; 16];

        /// When seeded with zero this implementation uses the default seed
        /// value as the cold path.
        fn from_seed(seed: Self::Seed) -> Self {
            let mut seed_u32s = [0u32; 4];
            if seed == [0; 16] {
                Self::cold_path_default()
            } else {
                for i in 0..4 {
                    seed_u32s[i] = u32::from_le_bytes([
                        seed[i * 4],
                        seed[i * 4 + 1],
                        seed[i * 4 + 2],
                        seed[i * 4 + 3],
                    ]);
                }
                Self::new_unchecked(seed_u32s)
            }
        }
    }

    impl RngCore for XorShift128p {
        /// Returns the next random `u32`,
        /// from the first 32-bits of `next_u64`.
        fn next_u32(&mut self) -> u32 {
            (self.next_u64() & 0xFFFF_FFFF) as u32
        }

        /// Returns the next random `u64`.
        fn next_u64(&mut self) -> u64 {
            self.next_u64()
        }

        fn fill_bytes(&mut self, dest: &mut [u8]) {
            let mut i = 0;
            while i < dest.len() {
                let random_u64 = self.next_u64();
                let bytes = random_u64.to_le_bytes();
                let remaining = dest.len() - i;

                if remaining >= 8 {
                    dest[i..i + 8].copy_from_slice(&bytes);
                    i += 8;
                } else {
                    dest[i..].copy_from_slice(&bytes[..remaining]);
                    break;
                }
            }
        }

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

    impl SeedableRng for XorShift128p {
        type Seed = [u8; 16];

        /// When seeded with zero this implementation uses the default seed
        /// value as the cold path.
        fn from_seed(seed: Self::Seed) -> Self {
            let mut seed_u64s = [0u64; 2];
            if seed == [0; 16] {
                Self::cold_path_default()
            } else {
                for i in 0..2 {
                    seed_u64s[i] = u64::from_le_bytes([
                        seed[i * 8],
                        seed[i * 8 + 1],
                        seed[i * 8 + 2],
                        seed[i * 8 + 3],
                        seed[i * 8 + 4],
                        seed[i * 8 + 5],
                        seed[i * 8 + 6],
                        seed[i * 8 + 7],
                    ]);
                }
                Self::new_unchecked(seed_u64s)
            }
        }
    }
}