Allow the optimizing code generator to call Math.pow with untagged doubles.

src/assembler.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 48 matching lines @@
 #error "Unknown architecture."
 #endif  // Target architecture.
 #endif  // V8_INTERPRETED_REGEXP
 
 namespace v8 {
 namespace internal {
 
 
 const double DoubleConstant::min_int = kMinInt;
 const double DoubleConstant::one_half = 0.5;
+const double DoubleConstant::negative_infinity = -V8_INFINITY;
 
 
 // -----------------------------------------------------------------------------
 // Implementation of Label
 
 int Label::pos() const {
   if (pos_ < 0) return -pos_ - 1;
   if (pos_ > 0) return  pos_ - 1;
   UNREACHABLE();
   return 0;
@@ skipping 636 matching lines @@
       const_cast<double*>(&DoubleConstant::min_int)));
 }
 
 
 ExternalReference ExternalReference::address_of_one_half() {
   return ExternalReference(reinterpret_cast<void*>(
       const_cast<double*>(&DoubleConstant::one_half)));
 }
 
 
+ExternalReference ExternalReference::address_of_negative_infinity() {
+  return ExternalReference(reinterpret_cast<void*>(
+      const_cast<double*>(&DoubleConstant::negative_infinity)));
+}
+
+
 #ifndef V8_INTERPRETED_REGEXP
 
 ExternalReference ExternalReference::re_check_stack_guard_state() {
   Address function;
 #ifdef V8_TARGET_ARCH_X64
   function = FUNCTION_ADDR(RegExpMacroAssemblerX64::CheckStackGuardState);
 #elif V8_TARGET_ARCH_IA32
   function = FUNCTION_ADDR(RegExpMacroAssemblerIA32::CheckStackGuardState);
 #elif V8_TARGET_ARCH_ARM
   function = FUNCTION_ADDR(RegExpMacroAssemblerARM::CheckStackGuardState);
@@ skipping 49 matching lines @@
 
 
 static double div_two_doubles(double x, double y) {
   return x / y;
 }
 
 
 static double mod_two_doubles(double x, double y) {
   return modulo(x, y);
 }
 

[fschneider, 2010/12/08 11:27:07]

It would be good to not duplicate code between here and runtime.cc.

[William Hesse, 2010/12/08 13:37:00]

Done.

 
+// Helper function to compute x^y, where y is known to be an
+// integer. Uses binary decomposition to limit the number of
+// multiplications; see the discussion in "Hacker's Delight" by Henry
+// S. Warren, Jr., figure 11-6, page 213.
+static double powi(double x, int y) {
+  unsigned n = (y < 0) ? -y : y;
+  double m = x;
+  double p = 1;
+  while (n != 0) {
+    if ((n & 1) != 0) p *= m;
+    m *= m;
+    if ((n & 2) != 0) p *= m;
+    m *= m;
+    n >>= 2;
+  }
+  if (y < 0) {
+    // Unfortunately, we have to be careful when p has reached
+    // infinity in the computation, because sometimes the higher
+    // internal precision in the pow() implementation would have
+    // given us a finite p. This happens very rarely.
+    double result = 1.0 / p;
+    return (result == 0 && isinf(p))
+        ? pow(x, static_cast<double>(y))  // Avoid pow(double, int).
+        : result;
+  } else {
+    return p;
+  }
+}
+
+
+static double power_two_doubles(double x, double y) {
+  int y_int = static_cast<int>(y);
+  if (y == y_int) {
+    return powi(x, y_int);
+  }
+  if (!isinf(x)) {
+    if (y == 0.5) return sqrt(x);
+    if (y == -0.5) return 1.0 / sqrt(x);
+  }
+  if (y == 0) return 1.0;
+  if (isnan(y) || ((x == 1 || x == -1) && isinf(y))) {
+    return OS::nan_value();
+  }
+  return pow(x, y);
+}
+
+
+static double power_double_int(double x, int y) {
+  return powi(x, y);
+}
+
+
 static int native_compare_doubles(double y, double x) {
   if (x == y) return EQUAL;
   return x < y ? LESS : GREATER;
 }
 
 
 ExternalReference ExternalReference::double_fp_operation(
     Token::Value operation) {
   typedef double BinaryFPOperation(double x, double y);
   BinaryFPOperation* function = NULL;
   switch (operation) {
     case Token::ADD:
       function = &add_two_doubles;
       break;
     case Token::SUB:
       function = &sub_two_doubles;
       break;
     case Token::MUL:
       function = &mul_two_doubles;
       break;
     case Token::DIV:
       function = &div_two_doubles;
       break;
     case Token::MOD:
       function = &mod_two_doubles;
       break;
+    case Token::BIT_XOR:

[Kevin Millikin (Chromium), 2010/12/08 10:01:46]

Don't repurpose these tokens this way, it's a bug waiting to happen.

Introduce an enumeration in ExternalReference for the operation (and a function
to convert token to operation for the one call site in ARM that needs it).

[William Hesse, 2010/12/08 13:37:00]

I removed the power case.  Did not change the existing code.

On 2010/12/08 10:01:46, Kevin Millikin wrote:
Done.

+      function = &power_two_doubles;
+      break;
+    case Token::BIT_OR:
+      function = reinterpret_cast<BinaryFPOperation*>(&power_double_int);
+      break;
     default:
       UNREACHABLE();
   }
   // Passing true as 2nd parameter indicates that they return an fp value.
   return ExternalReference(Redirect(FUNCTION_ADDR(function), true));
 }
 
 
 ExternalReference ExternalReference::compare_doubles() {
   return ExternalReference(Redirect(FUNCTION_ADDR(native_compare_doubles),
@@ skipping 51 matching lines @@
     assembler_->RecordRelocInfo(RelocInfo::POSITION, state_.current_position);
     state_.written_position = state_.current_position;
     written = true;
   }
 
   // Return whether something was written.
   return written;
 }
 
 } }  // namespace v8::internal