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// Copyright 2013 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "src/flags.h"
#include "src/isolate.h"
#include "src/v8.h"
#include "test/cctest/cctest.h"
#include "src/base/utils/random-number-generator.h"
namespace v8 {
namespace internal {
static const int64_t kRandomSeeds[] = {-1, 1, 42, 100, 1234567890, 987654321};
TEST(RandomSeedFlagIsUsed) {
for (unsigned n = 0; n < arraysize(kRandomSeeds); ++n) {
FLAG_random_seed = static_cast<int>(kRandomSeeds[n]);
v8::Isolate::CreateParams create_params;
create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
v8::Isolate* i = v8::Isolate::New(create_params);
v8::base::RandomNumberGenerator& rng =
*reinterpret_cast<Isolate*>(i)->random_number_generator();
CHECK_EQ(kRandomSeeds[n], rng.initial_seed());
i->Dispose();
}
}
// Chi squared for getting m 0s out of n bits.
double ChiSquared(int m, int n) {
double ys_minus_np1 = (m - n / 2.0);
double chi_squared_1 = ys_minus_np1 * ys_minus_np1 * 2.0 / n;
double ys_minus_np2 = ((n - m) - n / 2.0);
double chi_squared_2 = ys_minus_np2 * ys_minus_np2 * 2.0 / n;
return chi_squared_1 + chi_squared_2;
}
// Test for correlations between recent bits from the PRNG, or bits that are
// biased.
void RandomBitCorrelation(int random_bit) {
FLAG_random_seed = 31415926;
v8::Isolate::CreateParams create_params;
create_params.array_buffer_allocator = CcTest::array_buffer_allocator();
v8::Isolate* isolate = v8::Isolate::New(create_params);
Isolate* i_isolate = reinterpret_cast<Isolate*>(isolate);
v8::base::RandomNumberGenerator* rng = i_isolate->random_number_generator();
#ifdef DEBUG
const int kHistory = 2;
const int kRepeats = 1000;
#else
const int kHistory = 8;
const int kRepeats = 10000;
#endif
uint32_t history[kHistory];
// The predictor bit is either constant 0 or 1, or one of the bits from the
// history.
for (int predictor_bit = -2; predictor_bit < 32; predictor_bit++) {
// The predicted bit is one of the bits from the PRNG.
for (int ago = 0; ago < kHistory; ago++) {
// We don't want to check whether each bit predicts itself.
if (ago == 0 && predictor_bit == random_bit) continue;
// Enter the new random value into the history
for (int i = ago; i >= 0; i--) {
history[i] = bit_cast<uint32_t>(rng->NextInt());
}
// Find out how many of the bits are the same as the prediction bit.
int m = 0;
for (int i = 0; i < kRepeats; i++) {
v8::HandleScope scope(isolate);
uint32_t random = bit_cast<uint32_t>(rng->NextInt());
for (int j = ago - 1; j >= 0; j--) history[j + 1] = history[j];
history[0] = random;
int predicted;
if (predictor_bit >= 0) {
predicted = (history[ago] >> predictor_bit) & 1;
} else {
predicted = predictor_bit == -2 ? 0 : 1;
}
int bit = (random >> random_bit) & 1;
if (bit == predicted) m++;
}
// Chi squared analysis for k = 2 (2, states: same/not-same) and one
// degree of freedom (k - 1).
double chi_squared = ChiSquared(m, kRepeats);
if (chi_squared > 24) {
int percent = static_cast<int>(m * 100.0 / kRepeats);
if (predictor_bit < 0) {
PrintF("Bit %d is %d %d%% of the time\n", random_bit,
predictor_bit == -2 ? 0 : 1, percent);
} else {
PrintF("Bit %d is the same as bit %d %d ago %d%% of the time\n",
random_bit, predictor_bit, ago, percent);
}
}
// For 1 degree of freedom this corresponds to 1 in a million. We are
// running ~8000 tests, so that would be surprising.
CHECK_LE(chi_squared, 24);
// If the predictor bit is a fixed 0 or 1 then it makes no sense to
// repeat the test with a different age.
if (predictor_bit < 0) break;
}
}
isolate->Dispose();
}
#define TEST_RANDOM_BIT(BIT) \
TEST(RandomBitCorrelations##BIT) { RandomBitCorrelation(BIT); }
TEST_RANDOM_BIT(0)
TEST_RANDOM_BIT(1)
TEST_RANDOM_BIT(2)
TEST_RANDOM_BIT(3)
TEST_RANDOM_BIT(4)
TEST_RANDOM_BIT(5)
TEST_RANDOM_BIT(6)
TEST_RANDOM_BIT(7)
TEST_RANDOM_BIT(8)
TEST_RANDOM_BIT(9)
TEST_RANDOM_BIT(10)
TEST_RANDOM_BIT(11)
TEST_RANDOM_BIT(12)
TEST_RANDOM_BIT(13)
TEST_RANDOM_BIT(14)
TEST_RANDOM_BIT(15)
TEST_RANDOM_BIT(16)
TEST_RANDOM_BIT(17)
TEST_RANDOM_BIT(18)
TEST_RANDOM_BIT(19)
TEST_RANDOM_BIT(20)
TEST_RANDOM_BIT(21)
TEST_RANDOM_BIT(22)
TEST_RANDOM_BIT(23)
TEST_RANDOM_BIT(24)
TEST_RANDOM_BIT(25)
TEST_RANDOM_BIT(26)
TEST_RANDOM_BIT(27)
TEST_RANDOM_BIT(28)
TEST_RANDOM_BIT(29)
TEST_RANDOM_BIT(30)
TEST_RANDOM_BIT(31)
#undef TEST_RANDOM_BIT
} // namespace internal
} // namespace v8
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