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

src/assembler.cc

Index: src/assembler.cc
===================================================================
--- src/assembler.cc	(revision 5948)
+++ 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 +800,51 @@
 }
 
 
+// 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.
+double power_double_int(double x, int y) {
+  double m = (y < 0) ? 1/x : x;

[Florian Schneider, 2010/12/08 14:09:27]

--> 1 / x

[William Hesse, 2010/12/08 14:53:16]

Done.

+  unsigned n = (y < 0) ? -y : y;
+  double p = 1;
+  while (n != 0) {
+    if ((n & 1) != 0) p *= m;
+    m *= m;
+    if ((n & 2) != 0) p *= m;
+    m *= m;
+    n >>= 2;
+  }
+  return p;
+}
+
+
+double power_double_double(double x, double y) {
+  int y_int = static_cast<int>(y);
+  if (y == y_int) {
+    return power_double_int(x, y_int);  // Returns 1.0 for exponent 0.
+  }
+  if (!isinf(x)) {
+    if (y == 0.5) return sqrt(x);
+    if (y == -0.5) return 1.0 / sqrt(x);
+  }
+  if (isnan(y) || ((x == 1 || x == -1) && isinf(y))) {
+    return OS::nan_value();
+  }
+  return pow(x, y);
+}
+
+
+ExternalReference ExternalReference::power_double_double_function() {
+  return ExternalReference(Redirect(FUNCTION_ADDR(power_double_double)));
+}
+
+
+ExternalReference ExternalReference::power_double_int_function() {
+  return ExternalReference(Redirect(FUNCTION_ADDR(power_double_int)));
+}
+
+
 static int native_compare_doubles(double y, double x) {
   if (x == y) return EQUAL;
   return x < y ? LESS : GREATER;