Faster implementation of Math.exp()

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index aa777baf50ecf36e194474c9c79fa7ca96abcc58..e2471e69cc726d69c1eed338ac333558a8be6b9f 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -99,6 +99,36 @@ UnaryMathFunction CreateTranscendentalFunction(TranscendentalCache::Type type) {
 }
 
 
+UnaryMathFunction CreateExpFunction() {
+  if (!FLAG_fast_math) return &exp;
+  size_t actual_size;
+  byte* buffer = static_cast<byte*>(OS::Allocate(1 * KB, &actual_size, true));
+  if (buffer == NULL) return &exp;
+  ExternalReference::InitializeMathExpData();
+
+  MacroAssembler masm(NULL, buffer, static_cast<int>(actual_size));
+  // xmm0: raw double input.
+  XMMRegister input = xmm0;
+  XMMRegister result = xmm1;
+  __ push(rax);
+  __ push(rbx);
+
+  MathExpGenerator::EmitMathExp(&masm, input, result, xmm2, rax, rbx);
+
+  __ pop(rbx);
+  __ pop(rax);
+  __ movsd(xmm0, result);
+  __ Ret();
+
+  CodeDesc desc;
+  masm.GetCode(&desc);
+
+  CPU::FlushICache(buffer, actual_size);
+  OS::ProtectCode(buffer, actual_size);
+  return FUNCTION_CAST<UnaryMathFunction>(buffer);
+}
+
+
 UnaryMathFunction CreateSqrtFunction() {
   size_t actual_size;
   // Allocate buffer in executable space.
@@ -575,6 +605,58 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ bind(&done);
 }
 
+
+void MathExpGenerator::EmitMathExp(MacroAssembler* masm,
+                                   XMMRegister input,
+                                   XMMRegister result,
+                                   XMMRegister double_scratch,
+                                   Register temp1,
+                                   Register temp2) {
+  ASSERT(!input.is(result));
+  ASSERT(!input.is(double_scratch));
+  ASSERT(!result.is(double_scratch));
+  ASSERT(!temp1.is(temp2));
+  ASSERT(ExternalReference::math_exp_constants(0).address() != NULL);
+
+  Label done;
+
+  __ movq(kScratchRegister, ExternalReference::math_exp_constants(0));
+  __ movsd(double_scratch, Operand(kScratchRegister, 0 * kDoubleSize));
+  __ xorpd(result, result);
+  __ ucomisd(double_scratch, input);
+  __ j(above_equal, &done);
+  __ ucomisd(input, Operand(kScratchRegister, 1 * kDoubleSize));
+  __ movsd(result, Operand(kScratchRegister, 2 * kDoubleSize));
+  __ j(above_equal, &done);
+  __ movsd(double_scratch, Operand(kScratchRegister, 3 * kDoubleSize));
+  __ movsd(result, Operand(kScratchRegister, 4 * kDoubleSize));
+  __ mulsd(double_scratch, input);
+  __ addsd(double_scratch, result);
+  __ movq(temp2, double_scratch);
+  __ subsd(double_scratch, result);
+  __ movsd(result, Operand(kScratchRegister, 6 * kDoubleSize));
+  __ lea(temp1, Operand(temp2, 0x1ff800));
+  __ and_(temp2, Immediate(0x7ff));
+  __ shr(temp1, Immediate(11));
+  __ mulsd(double_scratch, Operand(kScratchRegister, 5 * kDoubleSize));
+  __ movq(kScratchRegister, ExternalReference::math_exp_log_table());
+  __ shl(temp1, Immediate(52));
+  __ or_(temp1, Operand(kScratchRegister, temp2, times_8, 0));
+  __ movq(kScratchRegister, ExternalReference::math_exp_constants(0));
+  __ subsd(double_scratch, input);
+  __ movsd(input, double_scratch);
+  __ subsd(result, double_scratch);
+  __ mulsd(input, double_scratch);
+  __ mulsd(result, input);
+  __ movq(input, temp1);
+  __ mulsd(result, Operand(kScratchRegister, 7 * kDoubleSize));
+  __ subsd(result, double_scratch);
+  __ addsd(result, Operand(kScratchRegister, 8 * kDoubleSize));
+  __ mulsd(result, input);
+
+  __ bind(&done);
+}
+
 #undef __