1 // Copyright 2018 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 #include "src/numbers/math-random.h"
6
7 #include "src/base/utils/random-number-generator.h"
8 #include "src/common/assert-scope.h"
9 #include "src/execution/isolate.h"
10 #include "src/objects/contexts-inl.h"
11 #include "src/objects/fixed-array.h"
12 #include "src/objects/smi.h"
13
14 namespace v8 {
15 namespace internal {
16
InitializeContext(Isolate * isolate,Handle<Context> native_context)17 void MathRandom::InitializeContext(Isolate* isolate,
18 Handle<Context> native_context) {
19 Handle<FixedDoubleArray> cache = Handle<FixedDoubleArray>::cast(
20 isolate->factory()->NewFixedDoubleArray(kCacheSize));
21 for (int i = 0; i < kCacheSize; i++) cache->set(i, 0);
22 native_context->set_math_random_cache(*cache);
23 Handle<PodArray<State>> pod =
24 PodArray<State>::New(isolate, 1, AllocationType::kOld);
25 native_context->set_math_random_state(*pod);
26 ResetContext(*native_context);
27 }
28
ResetContext(Context native_context)29 void MathRandom::ResetContext(Context native_context) {
30 native_context.set_math_random_index(Smi::zero());
31 State state = {0, 0};
32 PodArray<State>::cast(native_context.math_random_state()).set(0, state);
33 }
34
RefillCache(Isolate * isolate,Address raw_native_context)35 Address MathRandom::RefillCache(Isolate* isolate, Address raw_native_context) {
36 Context native_context = Context::cast(Object(raw_native_context));
37 DisallowGarbageCollection no_gc;
38 PodArray<State> pod =
39 PodArray<State>::cast(native_context.math_random_state());
40 State state = pod.get(0);
41 // Initialize state if not yet initialized. If a fixed random seed was
42 // requested, use it to reset our state the first time a script asks for
43 // random numbers in this context. This ensures the script sees a consistent
44 // sequence.
45 if (state.s0 == 0 && state.s1 == 0) {
46 uint64_t seed;
47 if (FLAG_random_seed != 0) {
48 seed = FLAG_random_seed;
49 } else {
50 isolate->random_number_generator()->NextBytes(&seed, sizeof(seed));
51 }
52 state.s0 = base::RandomNumberGenerator::MurmurHash3(seed);
53 state.s1 = base::RandomNumberGenerator::MurmurHash3(~seed);
54 CHECK(state.s0 != 0 || state.s1 != 0);
55 }
56
57 FixedDoubleArray cache =
58 FixedDoubleArray::cast(native_context.math_random_cache());
59 // Create random numbers.
60 for (int i = 0; i < kCacheSize; i++) {
61 // Generate random numbers using xorshift128+.
62 base::RandomNumberGenerator::XorShift128(&state.s0, &state.s1);
63 cache.set(i, base::RandomNumberGenerator::ToDouble(state.s0));
64 }
65 pod.set(0, state);
66
67 Smi new_index = Smi::FromInt(kCacheSize);
68 native_context.set_math_random_index(new_index);
69 return new_index.ptr();
70 }
71
72 } // namespace internal
73 } // namespace v8
74