Fix incorrect Math.pow() calculations on MinGW-w64.

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 1135 matching lines @@
     m *= m;
     if ((n & 2) != 0) p *= m;
     m *= m;
     n >>= 2;
   }
   return p;
 }
 
 
 double power_double_double(double x, double y) {
+#ifdef __MINGW64_VERSION_MAJOR
+  // MinGW64 has a custom implementation for pow.  This handles certain
+  // special cases that are different.
+  if ((x == 0.0 || isinf(x)) && isfinite(y)) {
+    double f;
+    if (modf(y, &f) != 0.0) return ((x == 0.0) ^ (y > 0)) ? V8_INFINITY : 0;
+  }
+
+  if (x == 2.0) {
+    int y_int = static_cast<int>(y);
+    if (y == y_int) return ldexp(1.0, y);
+  }
+#endif
+
   // The checks for special cases can be dropped in ia32 because it has already
   // been done in generated code before bailing out here.
   if (isnan(y) || ((x == 1 || x == -1) && isinf(y))) return OS::nan_value();
   return pow(x, y);
 }
 
 
 ExternalReference ExternalReference::power_double_double_function(
     Isolate* isolate) {
   return ExternalReference(Redirect(isolate,
@@ skipping 127 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