| // Copyright 2013 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "src/base/utils/random-number-generator.h" |
| |
| #include <stdio.h> |
| #include <stdlib.h> |
| |
| #include <new> |
| |
| #include "src/base/macros.h" |
| #include "src/base/platform/mutex.h" |
| #include "src/base/platform/time.h" |
| |
| namespace v8 { |
| namespace base { |
| |
| static LazyMutex entropy_mutex = LAZY_MUTEX_INITIALIZER; |
| static RandomNumberGenerator::EntropySource entropy_source = NULL; |
| |
| |
| // static |
| void RandomNumberGenerator::SetEntropySource(EntropySource source) { |
| LockGuard<Mutex> lock_guard(entropy_mutex.Pointer()); |
| entropy_source = source; |
| } |
| |
| |
| RandomNumberGenerator::RandomNumberGenerator() { |
| // Check if embedder supplied an entropy source. |
| { LockGuard<Mutex> lock_guard(entropy_mutex.Pointer()); |
| if (entropy_source != NULL) { |
| int64_t seed; |
| if (entropy_source(reinterpret_cast<unsigned char*>(&seed), |
| sizeof(seed))) { |
| SetSeed(seed); |
| return; |
| } |
| } |
| } |
| |
| #if V8_OS_CYGWIN || V8_OS_WIN |
| // Use rand_s() to gather entropy on Windows. See: |
| // https://code.google.com/p/v8/issues/detail?id=2905 |
| unsigned first_half, second_half; |
| errno_t result = rand_s(&first_half); |
| DCHECK_EQ(0, result); |
| result = rand_s(&second_half); |
| DCHECK_EQ(0, result); |
| SetSeed((static_cast<int64_t>(first_half) << 32) + second_half); |
| #else |
| // Gather entropy from /dev/urandom if available. |
| FILE* fp = fopen("/dev/urandom", "rb"); |
| if (fp != NULL) { |
| int64_t seed; |
| size_t n = fread(&seed, sizeof(seed), 1, fp); |
| fclose(fp); |
| if (n == 1) { |
| SetSeed(seed); |
| return; |
| } |
| } |
| |
| // We cannot assume that random() or rand() were seeded |
| // properly, so instead of relying on random() or rand(), |
| // we just seed our PRNG using timing data as fallback. |
| // This is weak entropy, but it's sufficient, because |
| // it is the responsibility of the embedder to install |
| // an entropy source using v8::V8::SetEntropySource(), |
| // which provides reasonable entropy, see: |
| // https://code.google.com/p/v8/issues/detail?id=2905 |
| int64_t seed = Time::NowFromSystemTime().ToInternalValue() << 24; |
| seed ^= TimeTicks::HighResolutionNow().ToInternalValue() << 16; |
| seed ^= TimeTicks::Now().ToInternalValue() << 8; |
| SetSeed(seed); |
| #endif // V8_OS_CYGWIN || V8_OS_WIN |
| } |
| |
| |
| int RandomNumberGenerator::NextInt(int max) { |
| DCHECK_LT(0, max); |
| |
| // Fast path if max is a power of 2. |
| if (IS_POWER_OF_TWO(max)) { |
| return static_cast<int>((max * static_cast<int64_t>(Next(31))) >> 31); |
| } |
| |
| while (true) { |
| int rnd = Next(31); |
| int val = rnd % max; |
| if (rnd - val + (max - 1) >= 0) { |
| return val; |
| } |
| } |
| } |
| |
| |
| double RandomNumberGenerator::NextDouble() { |
| XorShift128(&state0_, &state1_); |
| return ToDouble(state0_, state1_); |
| } |
| |
| |
| int64_t RandomNumberGenerator::NextInt64() { |
| XorShift128(&state0_, &state1_); |
| return bit_cast<int64_t>(state0_ + state1_); |
| } |
| |
| |
| void RandomNumberGenerator::NextBytes(void* buffer, size_t buflen) { |
| for (size_t n = 0; n < buflen; ++n) { |
| static_cast<uint8_t*>(buffer)[n] = static_cast<uint8_t>(Next(8)); |
| } |
| } |
| |
| |
| int RandomNumberGenerator::Next(int bits) { |
| DCHECK_LT(0, bits); |
| DCHECK_GE(32, bits); |
| XorShift128(&state0_, &state1_); |
| return static_cast<int>((state0_ + state1_) >> (64 - bits)); |
| } |
| |
| |
| void RandomNumberGenerator::SetSeed(int64_t seed) { |
| initial_seed_ = seed; |
| state0_ = MurmurHash3(bit_cast<uint64_t>(seed)); |
| state1_ = MurmurHash3(~state0_); |
| CHECK(state0_ != 0 || state1_ != 0); |
| } |
| |
| |
| uint64_t RandomNumberGenerator::MurmurHash3(uint64_t h) { |
| h ^= h >> 33; |
| h *= V8_UINT64_C(0xFF51AFD7ED558CCD); |
| h ^= h >> 33; |
| h *= V8_UINT64_C(0xC4CEB9FE1A85EC53); |
| h ^= h >> 33; |
| return h; |
| } |
| |
| } // namespace base |
| } // namespace v8 |