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

src/assembler.cc

Index: src/assembler.cc
===================================================================
--- src/assembler.cc	(revision 5940)
+++ src/assembler.cc	(working copy)
@@ -66,6 +66,7 @@
 
 const double DoubleConstant::min_int = kMinInt;
 const double DoubleConstant::one_half = 0.5;
+const double DoubleConstant::negative_infinity = -V8_INFINITY;
 
 
 // -----------------------------------------------------------------------------
@@ -722,6 +723,12 @@
 }
 
 
+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() {
@@ -793,6 +800,58 @@
 }
 

[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;
@@ -819,6 +878,12 @@
     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();
   }