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Unified Diff: src/base/utils/random-number-generator.cc

Issue 1475493003: Revert of Implement xorshift128+ for Math.random. (Closed) Base URL: https://chromium.googlesource.com/v8/v8.git@master
Patch Set: Created 5 years, 1 month ago
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Index: src/base/utils/random-number-generator.cc
diff --git a/src/base/utils/random-number-generator.cc b/src/base/utils/random-number-generator.cc
index 53a37526714a127f8ad9bf68677e7d88eaae6496..4cf06a90473096d0101913cfdf788298db91f618 100644
--- a/src/base/utils/random-number-generator.cc
+++ b/src/base/utils/random-number-generator.cc
@@ -97,14 +97,15 @@
double RandomNumberGenerator::NextDouble() {
- XorShift128(&state0_, &state1_);
- return ToDouble(state0_, state1_);
+ return ((static_cast<int64_t>(Next(26)) << 27) + Next(27)) /
+ static_cast<double>(static_cast<int64_t>(1) << 53);
}
int64_t RandomNumberGenerator::NextInt64() {
- XorShift128(&state0_, &state1_);
- return bit_cast<int64_t>(state0_ + state1_);
+ uint64_t lo = bit_cast<unsigned>(Next(32));
+ uint64_t hi = bit_cast<unsigned>(Next(32));
+ return lo | (hi << 32);
}
@@ -118,25 +119,21 @@
int RandomNumberGenerator::Next(int bits) {
DCHECK_LT(0, bits);
DCHECK_GE(32, bits);
- XorShift128(&state0_, &state1_);
- return static_cast<int>((state0_ + state1_) >> (64 - bits));
+ // Do unsigned multiplication, which has the intended modulo semantics, while
+ // signed multiplication would expose undefined behavior.
+ uint64_t product = static_cast<uint64_t>(seed_) * kMultiplier;
+ // Assigning a uint64_t to an int64_t is implementation defined, but this
+ // should be OK. Use a static_cast to explicitly state that we know what we're
+ // doing. (Famous last words...)
+ int64_t seed = static_cast<int64_t>((product + kAddend) & kMask);
+ seed_ = seed;
+ return static_cast<int>(seed >> (48 - bits));
}
void RandomNumberGenerator::SetSeed(int64_t seed) {
initial_seed_ = seed;
- state0_ = MurmurHash3(bit_cast<uint64_t>(seed));
- state1_ = MurmurHash3(state0_);
-}
-
-
-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;
+ seed_ = (seed ^ kMultiplier) & kMask;
}
} // namespace base
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