70 lines
2.6 KiB
JavaScript
70 lines
2.6 KiB
JavaScript
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// Copyright 2015 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Flags: --random-seed=12
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(function() {
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var kHistory = 2;
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var kRepeats = 100;
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var history = new Uint32Array(kHistory);
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function random() {
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return (Math.random() * Math.pow(2, 32)) >>> 0;
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}
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function ChiSquared(m, n) {
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var ys_minus_np1 = (m - n / 2.0);
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var chi_squared_1 = ys_minus_np1 * ys_minus_np1 * 2.0 / n;
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var ys_minus_np2 = ((n - m) - n / 2.0);
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var chi_squared_2 = ys_minus_np2 * ys_minus_np2 * 2.0 / n;
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return chi_squared_1 + chi_squared_2;
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}
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for (var predictor_bit = -2; predictor_bit < 32; predictor_bit++) {
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// The predicted bit is one of the bits from the PRNG.
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for (var random_bit = 0; random_bit < 32; random_bit++) {
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for (var ago = 0; ago < kHistory; ago++) {
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// We don't want to check whether each bit predicts itself.
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if (ago == 0 && predictor_bit == random_bit) continue;
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// Enter the new random value into the history
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for (var i = ago; i >= 0; i--) {
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history[i] = random();
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}
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// Find out how many of the bits are the same as the prediction bit.
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var m = 0;
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for (var i = 0; i < kRepeats; i++) {
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for (var j = ago - 1; j >= 0; j--) history[j + 1] = history[j];
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history[0] = random();
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var predicted;
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if (predictor_bit >= 0) {
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predicted = (history[ago] >> predictor_bit) & 1;
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} else {
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predicted = predictor_bit == -2 ? 0 : 1;
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}
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var bit = (history[0] >> random_bit) & 1;
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if (bit == predicted) m++;
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}
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// Chi squared analysis for k = 2 (2, states: same/not-same) and one
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// degree of freedom (k - 1).
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var chi_squared = ChiSquared(m, kRepeats);
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if (chi_squared > 24) {
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var percent = Math.floor(m * 100.0 / kRepeats);
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if (predictor_bit < 0) {
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var bit_value = predictor_bit == -2 ? 0 : 1;
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print(`Bit ${random_bit} is ${bit_value} ${percent}% of the time`);
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} else {
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print(`Bit ${random_bit} is the same as bit ${predictor_bit} ` +
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`${ago} ago ${percent}% of the time`);
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}
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}
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// For 1 degree of freedom this corresponds to 1 in a million. We are
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// running ~8000 tests, so that would be surprising.
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assertTrue(chi_squared <= 24);
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// If the predictor bit is a fixed 0 or 1 then it makes no sense to
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// repeat the test with a different age.
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if (predictor_bit < 0) break;
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}
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}
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}
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})();
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