Faster implementation of Math.exp()

src/arm/codegen-arm.cc

Index: src/arm/codegen-arm.cc
diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index 52a62959ef1ebd195cd5cb7725f2fafbb2f6b6e1..689de9f4c64c34e50399de8fb6bb75e921d24672 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -31,11 +31,11 @@
 
 #include "codegen.h"
 #include "macro-assembler.h"
+#include "simulator-arm.h"
 
 namespace v8 {
 namespace internal {
 
-#define __ ACCESS_MASM(masm)
 
 UnaryMathFunction CreateTranscendentalFunction(TranscendentalCache::Type type) {
   switch (type) {
@@ -49,6 +49,74 @@ UnaryMathFunction CreateTranscendentalFunction(TranscendentalCache::Type type) {
 }
 
 
+#define __ masm.
+
+
+#if defined(USE_SIMULATOR)
+byte* fast_exp_arm_machine_code = NULL;
+double fast_exp_simulator(double x) {
+  return Simulator::current(Isolate::Current())->CallFP(
+      fast_exp_arm_machine_code, x, 0);
+}
+#endif
+
+
+UnaryMathFunction CreateExpFunction() {
+  if (!CpuFeatures::IsSupported(VFP2)) return &exp;
+  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));
+
+  {
+    CpuFeatures::Scope use_vfp(VFP2);
+    DoubleRegister input = d0;
+    DoubleRegister result = d1;
+    DoubleRegister double_scratch1 = d2;
+    DoubleRegister double_scratch2 = d3;
+    Register temp1 = r4;
+    Register temp2 = r5;
+    Register temp3 = r6;
+
+    if (masm.use_eabi_hardfloat()) {
+      // Input value is in d0 anyway, nothing to do.
+    } else {
+      __ vmov(input, r0, r1);
+    }
+    __ Push(temp3, temp2, temp1);
+    MathExpGenerator::EmitMathExp(
+        &masm, input, result, double_scratch1, double_scratch2,
+        temp1, temp2, temp3);
+    __ Pop(temp3, temp2, temp1);
+    if (masm.use_eabi_hardfloat()) {
+      __ vmov(d0, result);
+    } else {
+      __ vmov(r0, r1, result);
+    }
+    __ Ret();
+  }
+
+  CodeDesc desc;
+  masm.GetCode(&desc);
+
+  CPU::FlushICache(buffer, actual_size);
+  OS::ProtectCode(buffer, actual_size);
+
+#if !defined(USE_SIMULATOR)
+  return FUNCTION_CAST<UnaryMathFunction>(buffer);
+#else
+  fast_exp_arm_machine_code = buffer;
+  return &fast_exp_simulator;
+#endif
+}
+
+
+#undef __
+
+
 UnaryMathFunction CreateSqrtFunction() {
   return &sqrt;
 }
@@ -73,6 +141,8 @@ void StubRuntimeCallHelper::AfterCall(MacroAssembler* masm) const {
 // -------------------------------------------------------------------------
 // Code generators
 
+#define __ ACCESS_MASM(masm)
+
 void ElementsTransitionGenerator::GenerateMapChangeElementsTransition(
     MacroAssembler* masm) {
   // ----------- S t a t e -------------
@@ -450,6 +520,78 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ bind(&done);
 }
 
+
+static MemOperand ExpConstant(int index, Register base) {
+  return MemOperand(base, index * kDoubleSize);
+}
+
+
+void MathExpGenerator::EmitMathExp(MacroAssembler* masm,
+                                   DoubleRegister input,
+                                   DoubleRegister result,
+                                   DoubleRegister double_scratch1,
+                                   DoubleRegister double_scratch2,
+                                   Register temp1,
+                                   Register temp2,
+                                   Register temp3) {
+  ASSERT(!input.is(result));
+  ASSERT(!input.is(double_scratch1));
+  ASSERT(!input.is(double_scratch2));
+  ASSERT(!result.is(double_scratch1));
+  ASSERT(!result.is(double_scratch2));
+  ASSERT(!double_scratch1.is(double_scratch2));
+  ASSERT(!temp1.is(temp2));
+  ASSERT(!temp1.is(temp3));
+  ASSERT(!temp2.is(temp3));
+  ASSERT(ExternalReference::math_exp_constants(0).address() != NULL);
+
+  Label done;
+
+  __ mov(temp3, Operand(ExternalReference::math_exp_constants(0)));
+
+  __ vldr(double_scratch1, ExpConstant(0, temp3));
+  __ vmov(result, kDoubleRegZero);
+  __ VFPCompareAndSetFlags(double_scratch1, input);
+  __ b(ge, &done);
+  __ vldr(double_scratch2, ExpConstant(1, temp3));
+  __ VFPCompareAndSetFlags(input, double_scratch2);
+  __ vldr(result, ExpConstant(2, temp3));
+  __ b(ge, &done);
+  __ vldr(double_scratch1, ExpConstant(3, temp3));
+  __ vldr(result, ExpConstant(4, temp3));
+  __ vmul(double_scratch1, double_scratch1, input);
+  __ vadd(double_scratch1, double_scratch1, result);
+  __ vmov(temp2, temp1, double_scratch1);
+  __ vsub(double_scratch1, double_scratch1, result);
+  __ vldr(result, ExpConstant(6, temp3));
+  __ vldr(double_scratch2, ExpConstant(5, temp3));
+  __ vmul(double_scratch1, double_scratch1, double_scratch2);
+  __ vsub(double_scratch1, double_scratch1, input);
+  __ vsub(result, result, double_scratch1);
+  __ vmul(input, double_scratch1, double_scratch1);
+  __ vmul(result, result, input);
+  __ mov(temp1, Operand(temp2, LSR, 11));
+  __ vldr(double_scratch2, ExpConstant(7, temp3));
+  __ vmul(result, result, double_scratch2);
+  __ vsub(result, result, double_scratch1);
+  __ vldr(double_scratch2, ExpConstant(8, temp3));
+  __ vadd(result, result, double_scratch2);
+  __ movw(ip, 0x7ff);
+  __ and_(temp2, temp2, Operand(ip));
+  __ add(temp1, temp1, Operand(0x3ff));
+  __ mov(temp1, Operand(temp1, LSL, 20));
+
+  // Must not call ExpConstant() after overwriting temp3!
+  __ mov(temp3, Operand(ExternalReference::math_exp_log_table()));
+  __ ldr(ip, MemOperand(temp3, temp2, LSL, 3));
+  __ add(temp3, temp3, Operand(kPointerSize));
+  __ ldr(temp2, MemOperand(temp3, temp2, LSL, 3));
+  __ orr(temp1, temp1, temp2);
+  __ vmov(input, ip, temp1);
+  __ vmul(result, result, input);
+  __ bind(&done);
+}
+
 #undef __
 
 // add(r0, pc, Operand(-8))