Revert 17963, 17962 and 17955: Random number generator in JS changes

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index cd9c712d3eaf46c3d125e03bbac205612d960707..0aa8197ce1fe128098ef6f5c742592eb976f5653 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -3934,6 +3934,68 @@ void LCodeGen::DoPower(LPower* instr) {
 }
 
 
+void LCodeGen::DoRandom(LRandom* instr) {
+  // Assert that the register size is indeed the size of each seed.
+  static const int kSeedSize = sizeof(uint32_t);
+  STATIC_ASSERT(kPointerSize == kSeedSize);
+
+  // Load native context
+  Register global_object = ToRegister(instr->global_object());
+  Register native_context = global_object;
+  __ ldr(native_context, FieldMemOperand(
+          global_object, GlobalObject::kNativeContextOffset));
+
+  // Load state (FixedArray of the native context's random seeds)
+  static const int kRandomSeedOffset =
+      FixedArray::kHeaderSize + Context::RANDOM_SEED_INDEX * kPointerSize;
+  Register state = native_context;
+  __ ldr(state, FieldMemOperand(native_context, kRandomSeedOffset));
+
+  // Load state[0].
+  Register state0 = ToRegister(instr->scratch());
+  __ ldr(state0, FieldMemOperand(state, ByteArray::kHeaderSize));
+  // Load state[1].
+  Register state1 = ToRegister(instr->scratch2());
+  __ ldr(state1, FieldMemOperand(state, ByteArray::kHeaderSize + kSeedSize));
+
+  // state[0] = 18273 * (state[0] & 0xFFFF) + (state[0] >> 16)
+  Register scratch3 = ToRegister(instr->scratch3());
+  Register scratch4 = scratch0();
+  __ and_(scratch3, state0, Operand(0xFFFF));
+  __ mov(scratch4, Operand(18273));
+  __ mul(scratch3, scratch3, scratch4);
+  __ add(state0, scratch3, Operand(state0, LSR, 16));
+  // Save state[0].
+  __ str(state0, FieldMemOperand(state, ByteArray::kHeaderSize));
+
+  // state[1] = 36969 * (state[1] & 0xFFFF) + (state[1] >> 16)
+  __ and_(scratch3, state1, Operand(0xFFFF));
+  __ mov(scratch4, Operand(36969));
+  __ mul(scratch3, scratch3, scratch4);
+  __ add(state1, scratch3, Operand(state1, LSR, 16));
+  // Save state[1].
+  __ str(state1, FieldMemOperand(state, ByteArray::kHeaderSize + kSeedSize));
+
+  // Random bit pattern = (state[0] << 14) + (state[1] & 0x3FFFF)
+  Register random = scratch4;
+  __ and_(random, state1, Operand(0x3FFFF));
+  __ add(random, random, Operand(state0, LSL, 14));
+
+  // 0x41300000 is the top half of 1.0 x 2^20 as a double.
+  // Create this constant using mov/orr to avoid PC relative load.
+  __ mov(scratch3, Operand(0x41000000));
+  __ orr(scratch3, scratch3, Operand(0x300000));
+  // Move 0x41300000xxxxxxxx (x = random bits) to VFP.
+  DwVfpRegister result = ToDoubleRegister(instr->result());
+  __ vmov(result, random, scratch3);
+  // Move 0x4130000000000000 to VFP.
+  __ mov(scratch4, Operand::Zero());
+  DwVfpRegister scratch5 = double_scratch0();
+  __ vmov(scratch5, scratch4, scratch3);
+  __ vsub(result, result, scratch5);
+}
+
+
 void LCodeGen::DoMathExp(LMathExp* instr) {
   DwVfpRegister input = ToDoubleRegister(instr->value());
   DwVfpRegister result = ToDoubleRegister(instr->result());