OLD | NEW |
---|---|
(Empty) | |
1 // Copyright 2015 the V8 project authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 // Flags: --random-seed=12 | |
6 | |
7 (function() { | |
8 var kHistory = 2; | |
9 var kRepeats = 100; | |
10 var history = new Uint32Array(kHistory); | |
11 | |
12 function random() { | |
13 return (Math.random() * Math.pow(2, 32)) >>> 0; | |
erikcorry
2015/11/25 07:43:08
This doesn't test the low bits of the floating poi
| |
14 } | |
15 | |
16 function ChiSquared(m, n) { | |
17 var ys_minus_np1 = (m - n / 2.0); | |
18 var chi_squared_1 = ys_minus_np1 * ys_minus_np1 * 2.0 / n; | |
19 var ys_minus_np2 = ((n - m) - n / 2.0); | |
20 var chi_squared_2 = ys_minus_np2 * ys_minus_np2 * 2.0 / n; | |
21 return chi_squared_1 + chi_squared_2; | |
22 } | |
23 for (var predictor_bit = -2; predictor_bit < 32; predictor_bit++) { | |
24 // The predicted bit is one of the bits from the PRNG. | |
25 for (var random_bit = 0; random_bit < 32; random_bit++) { | |
26 for (var ago = 0; ago < kHistory; ago++) { | |
27 // We don't want to check whether each bit predicts itself. | |
28 if (ago == 0 && predictor_bit == random_bit) continue; | |
29 // Enter the new random value into the history | |
30 for (var i = ago; i >= 0; i--) { | |
31 history[i] = random(); | |
32 } | |
33 // Find out how many of the bits are the same as the prediction bit. | |
34 var m = 0; | |
35 for (var i = 0; i < kRepeats; i++) { | |
36 for (var j = ago - 1; j >= 0; j--) history[j + 1] = history[j]; | |
37 history[0] = random(); | |
38 var predicted; | |
39 if (predictor_bit >= 0) { | |
40 predicted = (history[ago] >> predictor_bit) & 1; | |
41 } else { | |
42 predicted = predictor_bit == -2 ? 0 : 1; | |
43 } | |
44 var bit = (history[0] >> random_bit) & 1; | |
45 if (bit == predicted) m++; | |
46 } | |
47 // Chi squared analysis for k = 2 (2, states: same/not-same) and one | |
48 // degree of freedom (k - 1). | |
49 var chi_squared = ChiSquared(m, kRepeats); | |
50 if (chi_squared > 24) { | |
51 var percent = Math.floor(m * 100.0 / kRepeats); | |
52 if (predictor_bit < 0) { | |
53 var bit_value = predictor_bit == -2 ? 0 : 1; | |
54 print(`Bit ${random_bit} is ${bit_value} ${percent}% of the time`); | |
55 } else { | |
56 print(`Bit ${random_bit} is the same as bit ${predictor_bit} ` + | |
57 `${ago} ago ${percent}% of the time`); | |
58 } | |
59 } | |
60 // For 1 degree of freedom this corresponds to 1 in a million. We are | |
61 // running ~8000 tests, so that would be surprising. | |
62 assertTrue(chi_squared <= 24); | |
63 // If the predictor bit is a fixed 0 or 1 then it makes no sense to | |
64 // repeat the test with a different age. | |
65 if (predictor_bit < 0) break; | |
66 } | |
67 } | |
68 } | |
69 })(); | |
OLD | NEW |