[Math] implement Math.random as TFJ builtin.

src/builtins/builtins-math.cc

Index: src/builtins/builtins-math.cc
diff --git a/src/builtins/builtins-math.cc b/src/builtins/builtins-math.cc
index 6058f12265a36fd3380f02ebf3e07865c0a905e6..29c87b4be2ab225849a046902e44e1f4ce8c9b20 100644
--- a/src/builtins/builtins-math.cc
+++ b/src/builtins/builtins-math.cc
@@ -452,6 +452,46 @@ void Builtins::Generate_MathPow(CodeStubAssembler* assembler) {
   assembler->Return(result);
 }
 
+// ES6 section 20.2.2.27 Math.random ( )
+void Builtins::Generate_MathRandom(CodeStubAssembler* assembler) {
+  using compiler::Node;
+
+  Node* context = assembler->Parameter(3);
+  Node* native_context = assembler->LoadNativeContext(context);
+
+  // Load cache index.
+  CodeStubAssembler::Variable smi_index(assembler,
+                                        MachineRepresentation::kTagged);
+  smi_index.Bind(assembler->LoadContextElement(
+      native_context, Context::MATH_RANDOM_INDEX_INDEX));
+
+  // Cached random numbers are exhausted if index is 0. Go to slow path.
+  CodeStubAssembler::Label if_cached(assembler);
+  assembler->GotoIf(assembler->SmiAbove(smi_index.value(),
+                                        assembler->SmiConstant(Smi::kZero)),
+                    &if_cached);
+
+  // Cache exhausted, populate the cache. Return value is the new index.
+  smi_index.Bind(
+      assembler->CallRuntime(Runtime::kGenerateRandomNumbers, context));
+  assembler->Goto(&if_cached);
+
+  // Compute next index by decrement.
+  assembler->Bind(&if_cached);
+  Node* new_smi_index = assembler->SmiSub(
+      smi_index.value(), assembler->SmiConstant(Smi::FromInt(1)));
+  assembler->StoreContextElement(
+      native_context, Context::MATH_RANDOM_INDEX_INDEX, new_smi_index);
+
+  // Load and return next cached random number.
+  Node* array = assembler->LoadContextElement(native_context,
+                                              Context::MATH_RANDOM_CACHE_INDEX);
+  Node* random = assembler->LoadFixedDoubleArrayElement(
+      array, new_smi_index, MachineType::Float64(), 0,
+      CodeStubAssembler::SMI_PARAMETERS);
+  assembler->Return(assembler->ChangeFloat64ToTagged(random));
+}
+
 // ES6 section 20.2.2.28 Math.round ( x )
 void Builtins::Generate_MathRound(CodeStubAssembler* assembler) {
   Generate_MathRoundingOperation(assembler, &CodeStubAssembler::Float64Round);