1const std = @import("../std.zig");
2const math = std.math;
3const Random = std.Random;
4const DefaultPrng = Random.DefaultPrng;
5const SplitMix64 = Random.SplitMix64;
6const DefaultCsprng = Random.DefaultCsprng;
7const expect = std.testing.expect;
8const expectEqual = std.testing.expectEqual;
9
10const SequentialPrng = struct {
11 const Self = @This();
12 next_value: u8,
13
14 pub fn init() Self {
15 return Self{
16 .next_value = 0,
17 };
18 }
19
20 pub fn random(self: *Self) Random {
21 return Random.init(self, fill);
22 }
23
24 pub fn fill(self: *Self, buf: []u8) void {
25 for (buf) |*b| {
26 b.* = self.next_value;
27 }
28 self.next_value +%= 1;
29 }
30};
31
32/// Do not use this PRNG! It is meant to be predictable, for the purposes of test reproducibility and coverage.
33/// Its output is just a repeat of a user-specified byte pattern.
34/// Name is a reference to this comic: https://dilbert.com/strip/2001-10-25
35const Dilbert = struct {
36 pattern: []const u8 = undefined,
37 curr_idx: usize = 0,
38
39 pub fn init(pattern: []const u8) !Dilbert {
40 if (pattern.len == 0)
41 return error.EmptyPattern;
42 var self = Dilbert{};
43 self.pattern = pattern;
44 self.curr_idx = 0;
45 return self;
46 }
47
48 pub fn random(self: *Dilbert) Random {
49 return Random.init(self, fill);
50 }
51
52 pub fn fill(self: *Dilbert, buf: []u8) void {
53 for (buf) |*byte| {
54 byte.* = self.pattern[self.curr_idx];
55 self.curr_idx = (self.curr_idx + 1) % self.pattern.len;
56 }
57 }
58
59 test "Dilbert fill" {
60 var r = try Dilbert.init("9nine");
61
62 const seq = [_]u64{
63 0x396E696E65396E69,
64 0x6E65396E696E6539,
65 0x6E696E65396E696E,
66 0x65396E696E65396E,
67 0x696E65396E696E65,
68 };
69
70 for (seq) |s| {
71 var buf0: [8]u8 = undefined;
72 var buf1: [8]u8 = undefined;
73 std.mem.writeInt(u64, &buf0, s, .big);
74 r.fill(&buf1);
75 try std.testing.expect(std.mem.eql(u8, buf0[0..], buf1[0..]));
76 }
77 }
78};
79
80test "Random int" {
81 try testRandomInt();
82 try comptime testRandomInt();
83}
84fn testRandomInt() !void {
85 var rng = SequentialPrng.init();
86 const random = rng.random();
87
88 try expect(random.int(u0) == 0);
89
90 rng.next_value = 0;
91 try expect(random.int(u1) == 0);
92 try expect(random.int(u1) == 1);
93 try expect(random.int(u2) == 2);
94 try expect(random.int(u2) == 3);
95 try expect(random.int(u2) == 0);
96
97 rng.next_value = 0xff;
98 try expect(random.int(u8) == 0xff);
99 rng.next_value = 0x11;
100 try expect(random.int(u8) == 0x11);
101
102 rng.next_value = 0xff;
103 try expect(random.int(u32) == 0xffffffff);
104 rng.next_value = 0x11;
105 try expect(random.int(u32) == 0x11111111);
106
107 rng.next_value = 0xff;
108 try expect(random.int(i32) == -1);
109 rng.next_value = 0x11;
110 try expect(random.int(i32) == 0x11111111);
111
112 rng.next_value = 0xff;
113 try expect(random.int(i8) == -1);
114 rng.next_value = 0x11;
115 try expect(random.int(i8) == 0x11);
116
117 rng.next_value = 0xff;
118 try expect(random.int(u33) == 0x1ffffffff);
119 rng.next_value = 0xff;
120 try expect(random.int(i1) == -1);
121 rng.next_value = 0xff;
122 try expect(random.int(i2) == -1);
123 rng.next_value = 0xff;
124 try expect(random.int(i33) == -1);
125}
126
127test "Random boolean" {
128 try testRandomBoolean();
129 try comptime testRandomBoolean();
130}
131fn testRandomBoolean() !void {
132 var rng = SequentialPrng.init();
133 const random = rng.random();
134
135 try expect(random.boolean() == false);
136 try expect(random.boolean() == true);
137 try expect(random.boolean() == false);
138 try expect(random.boolean() == true);
139}
140
141test "Random enum" {
142 try testRandomEnumValue();
143 try comptime testRandomEnumValue();
144}
145fn testRandomEnumValue() !void {
146 const TestEnum = enum {
147 First,
148 Second,
149 Third,
150 };
151 var rng = SequentialPrng.init();
152 const random = rng.random();
153 rng.next_value = 0;
154 try expect(random.enumValue(TestEnum) == TestEnum.First);
155 try expect(random.enumValue(TestEnum) == TestEnum.First);
156 try expect(random.enumValue(TestEnum) == TestEnum.First);
157}
158
159test "Random intLessThan" {
160 @setEvalBranchQuota(10000);
161 try testRandomIntLessThan();
162 try comptime testRandomIntLessThan();
163}
164fn testRandomIntLessThan() !void {
165 var rng = SequentialPrng.init();
166 const random = rng.random();
167
168 rng.next_value = 0xff;
169 try expect(random.uintLessThan(u8, 4) == 3);
170 try expect(rng.next_value == 0);
171 try expect(random.uintLessThan(u8, 4) == 0);
172 try expect(rng.next_value == 1);
173
174 rng.next_value = 0;
175 try expect(random.uintLessThan(u64, 32) == 0);
176
177 // trigger the bias rejection code path
178 rng.next_value = 0;
179 try expect(random.uintLessThan(u8, 3) == 0);
180 // verify we incremented twice
181 try expect(rng.next_value == 2);
182
183 rng.next_value = 0xff;
184 try expect(random.intRangeLessThan(u8, 0, 0x80) == 0x7f);
185 rng.next_value = 0xff;
186 try expect(random.intRangeLessThan(u8, 0x7f, 0xff) == 0xfe);
187
188 rng.next_value = 0xff;
189 try expect(random.intRangeLessThan(i8, 0, 0x40) == 0x3f);
190 rng.next_value = 0xff;
191 try expect(random.intRangeLessThan(i8, -0x40, 0x40) == 0x3f);
192 rng.next_value = 0xff;
193 try expect(random.intRangeLessThan(i8, -0x80, 0) == -1);
194
195 rng.next_value = 0xff;
196 try expect(random.intRangeLessThan(i3, -4, 0) == -1);
197 rng.next_value = 0xff;
198 try expect(random.intRangeLessThan(i3, -2, 2) == 1);
199}
200
201test "Random intAtMost" {
202 @setEvalBranchQuota(10000);
203 try testRandomIntAtMost();
204 try comptime testRandomIntAtMost();
205}
206fn testRandomIntAtMost() !void {
207 var rng = SequentialPrng.init();
208 const random = rng.random();
209
210 rng.next_value = 0xff;
211 try expect(random.uintAtMost(u8, 3) == 3);
212 try expect(rng.next_value == 0);
213 try expect(random.uintAtMost(u8, 3) == 0);
214
215 // trigger the bias rejection code path
216 rng.next_value = 0;
217 try expect(random.uintAtMost(u8, 2) == 0);
218 // verify we incremented twice
219 try expect(rng.next_value == 2);
220
221 rng.next_value = 0xff;
222 try expect(random.intRangeAtMost(u8, 0, 0x7f) == 0x7f);
223 rng.next_value = 0xff;
224 try expect(random.intRangeAtMost(u8, 0x7f, 0xfe) == 0xfe);
225
226 rng.next_value = 0xff;
227 try expect(random.intRangeAtMost(i8, 0, 0x3f) == 0x3f);
228 rng.next_value = 0xff;
229 try expect(random.intRangeAtMost(i8, -0x40, 0x3f) == 0x3f);
230 rng.next_value = 0xff;
231 try expect(random.intRangeAtMost(i8, -0x80, -1) == -1);
232
233 rng.next_value = 0xff;
234 try expect(random.intRangeAtMost(i3, -4, -1) == -1);
235 rng.next_value = 0xff;
236 try expect(random.intRangeAtMost(i3, -2, 1) == 1);
237
238 try expect(random.uintAtMost(u0, 0) == 0);
239}
240
241test "Random Biased" {
242 var prng = DefaultPrng.init(0);
243 const random = prng.random();
244 // Not thoroughly checking the logic here.
245 // Just want to execute all the paths with different types.
246
247 try expect(random.uintLessThanBiased(u1, 1) == 0);
248 try expect(random.uintLessThanBiased(u32, 10) < 10);
249 try expect(random.uintLessThanBiased(u64, 20) < 20);
250
251 try expect(random.uintAtMostBiased(u0, 0) == 0);
252 try expect(random.uintAtMostBiased(u1, 0) <= 0);
253 try expect(random.uintAtMostBiased(u32, 10) <= 10);
254 try expect(random.uintAtMostBiased(u64, 20) <= 20);
255
256 try expect(random.intRangeLessThanBiased(u1, 0, 1) == 0);
257 try expect(random.intRangeLessThanBiased(i1, -1, 0) == -1);
258 try expect(random.intRangeLessThanBiased(u32, 10, 20) >= 10);
259 try expect(random.intRangeLessThanBiased(i32, 10, 20) >= 10);
260 try expect(random.intRangeLessThanBiased(u64, 20, 40) >= 20);
261 try expect(random.intRangeLessThanBiased(i64, 20, 40) >= 20);
262
263 // uncomment for broken module error:
264 //expect(random.intRangeAtMostBiased(u0, 0, 0) == 0);
265 try expect(random.intRangeAtMostBiased(u1, 0, 1) >= 0);
266 try expect(random.intRangeAtMostBiased(i1, -1, 0) >= -1);
267 try expect(random.intRangeAtMostBiased(u32, 10, 20) >= 10);
268 try expect(random.intRangeAtMostBiased(i32, 10, 20) >= 10);
269 try expect(random.intRangeAtMostBiased(u64, 20, 40) >= 20);
270 try expect(random.intRangeAtMostBiased(i64, 20, 40) >= 20);
271}
272
273test "splitmix64 sequence" {
274 var r = SplitMix64.init(0xaeecf86f7878dd75);
275
276 const seq = [_]u64{
277 0x5dbd39db0178eb44,
278 0xa9900fb66b397da3,
279 0x5c1a28b1aeebcf5c,
280 0x64a963238f776912,
281 0xc6d4177b21d1c0ab,
282 0xb2cbdbdb5ea35394,
283 };
284
285 for (seq) |s| {
286 try expect(s == r.next());
287 }
288}
289
290// Actual Random helper function tests, pcg engine is assumed correct.
291test "Random float correctness" {
292 var prng = DefaultPrng.init(0);
293 const random = prng.random();
294
295 var i: usize = 0;
296 while (i < 1000) : (i += 1) {
297 const val1 = random.float(f32);
298 try expect(val1 >= 0.0);
299 try expect(val1 < 1.0);
300
301 const val2 = random.float(f64);
302 try expect(val2 >= 0.0);
303 try expect(val2 < 1.0);
304 }
305}
306
307// Check the "astronomically unlikely" code paths.
308test "Random float coverage" {
309 var prng = try Dilbert.init(&[_]u8{0});
310 const random = prng.random();
311
312 const rand_f64 = random.float(f64);
313 const rand_f32 = random.float(f32);
314
315 try expect(rand_f32 == 0.0);
316 try expect(rand_f64 == 0.0);
317}
318
319test "Random float chi-square goodness of fit" {
320 const num_numbers = 100000;
321 const num_buckets = 1000;
322
323 var f32_hist = std.AutoHashMap(u32, u32).init(std.testing.allocator);
324 defer f32_hist.deinit();
325 var f64_hist = std.AutoHashMap(u64, u32).init(std.testing.allocator);
326 defer f64_hist.deinit();
327
328 var prng = DefaultPrng.init(0);
329 const random = prng.random();
330
331 var i: usize = 0;
332 while (i < num_numbers) : (i += 1) {
333 const rand_f32 = random.float(f32);
334 const rand_f64 = random.float(f64);
335 const f32_put = try f32_hist.getOrPut(@as(u32, @intFromFloat(rand_f32 * @as(f32, @floatFromInt(num_buckets)))));
336 if (f32_put.found_existing) {
337 f32_put.value_ptr.* += 1;
338 } else {
339 f32_put.value_ptr.* = 1;
340 }
341 const f64_put = try f64_hist.getOrPut(@as(u32, @intFromFloat(rand_f64 * @as(f64, @floatFromInt(num_buckets)))));
342 if (f64_put.found_existing) {
343 f64_put.value_ptr.* += 1;
344 } else {
345 f64_put.value_ptr.* = 1;
346 }
347 }
348
349 var f32_total_variance: f64 = 0;
350 var f64_total_variance: f64 = 0;
351
352 {
353 var j: u32 = 0;
354 while (j < num_buckets) : (j += 1) {
355 const count = @as(f64, @floatFromInt((if (f32_hist.get(j)) |v| v else 0)));
356 const expected = @as(f64, @floatFromInt(num_numbers)) / @as(f64, @floatFromInt(num_buckets));
357 const delta = count - expected;
358 const variance = (delta * delta) / expected;
359 f32_total_variance += variance;
360 }
361 }
362
363 {
364 var j: u64 = 0;
365 while (j < num_buckets) : (j += 1) {
366 const count = @as(f64, @floatFromInt((if (f64_hist.get(j)) |v| v else 0)));
367 const expected = @as(f64, @floatFromInt(num_numbers)) / @as(f64, @floatFromInt(num_buckets));
368 const delta = count - expected;
369 const variance = (delta * delta) / expected;
370 f64_total_variance += variance;
371 }
372 }
373
374 // Accept p-values >= 0.05.
375 // Critical value is calculated by opening a Python interpreter and running:
376 // scipy.stats.chi2.isf(0.05, num_buckets - 1)
377 const critical_value = 1073.6426506574246;
378 try expect(f32_total_variance < critical_value);
379 try expect(f64_total_variance < critical_value);
380}
381
382test "Random shuffle" {
383 var prng = DefaultPrng.init(0);
384 const random = prng.random();
385
386 var seq: [5]u8 = .{ 0, 1, 2, 3, 4 };
387 var seen: [5]bool = @splat(false);
388
389 var i: usize = 0;
390 while (i < 1000) : (i += 1) {
391 random.shuffle(u8, seq[0..]);
392 seen[seq[0]] = true;
393 try expect(sumArray(seq[0..]) == 10);
394 }
395
396 // we should see every entry at the head at least once
397 for (seen) |e| {
398 try expect(e == true);
399 }
400}
401
402fn sumArray(s: []const u8) u32 {
403 var r: u32 = 0;
404 for (s) |e|
405 r += e;
406 return r;
407}
408
409test "Random range" {
410 var prng = DefaultPrng.init(0);
411 const random = prng.random();
412
413 try testRange(random, -4, 3);
414 try testRange(random, -4, -1);
415 try testRange(random, 10, 14);
416 try testRange(random, -0x80, 0x7f);
417}
418
419fn testRange(r: Random, start: i8, end: i8) !void {
420 try testRangeBias(r, start, end, true);
421 try testRangeBias(r, start, end, false);
422}
423fn testRangeBias(r: Random, start: i8, end: i8, biased: bool) !void {
424 const count: usize = @intCast(@as(i32, end) - @as(i32, start));
425 var values_buffer: [0x100]bool = @splat(false);
426 const values = values_buffer[0..count];
427 var i: usize = 0;
428 while (i < count) {
429 const value: i32 = if (biased) r.intRangeLessThanBiased(i8, start, end) else r.intRangeLessThan(i8, start, end);
430 const index = @as(usize, @intCast(value - start));
431 if (!values[index]) {
432 i += 1;
433 values[index] = true;
434 }
435 }
436}
437
438test "CSPRNG" {
439 const io = std.testing.io;
440 var secret_seed: [DefaultCsprng.secret_seed_length]u8 = undefined;
441 io.random(&secret_seed);
442 var csprng = DefaultCsprng.init(secret_seed);
443 const random = csprng.random();
444 const a = random.int(u64);
445 const b = random.int(u64);
446 const c = random.int(u64);
447 try expect(a ^ b ^ c != 0);
448}
449
450test "Random weightedIndex" {
451 // Make sure weightedIndex works for various integers and floats
452 inline for (.{ u64, i4, f32, f64 }) |T| {
453 var prng = DefaultPrng.init(0);
454 const random = prng.random();
455
456 const proportions = [_]T{ 2, 1, 1, 2 };
457 var counts = [_]f64{ 0, 0, 0, 0 };
458
459 const n_trials: u64 = 10_000;
460 var i: usize = 0;
461 while (i < n_trials) : (i += 1) {
462 const pick = random.weightedIndex(T, &proportions);
463 counts[pick] += 1;
464 }
465
466 // We expect the first and last counts to be roughly 2x the second and third
467 const approxEqRel = std.math.approxEqRel;
468 // Define "roughly" to be within 10%
469 const tolerance = 0.1;
470 try std.testing.expect(approxEqRel(f64, counts[0], counts[1] * 2, tolerance));
471 try std.testing.expect(approxEqRel(f64, counts[1], counts[2], tolerance));
472 try std.testing.expect(approxEqRel(f64, counts[2] * 2, counts[3], tolerance));
473 }
474}