Tweaks on Math.pow (ia32 and x64).

src/runtime.cc

 // Copyright 2011 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 7380 matching lines @@
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_log) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
   isolate->counters()->math_log()->Increment();
 
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
   return isolate->transcendental_cache()->Get(TranscendentalCache::LOG, x);
 }
 
-
+// Slow version of Math.pow.  We check for fast paths for special cases.
+// Used if SSE2/VFP3 is not available.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_pow) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 2);
   isolate->counters()->math_pow()->Increment();
 
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
 
   // If the second argument is a smi, it is much faster to call the
   // custom powi() function than the generic pow().
   if (args[1]->IsSmi()) {
     int y = args.smi_at(1);
     return isolate->heap()->NumberFromDouble(power_double_int(x, y));
   }
 
   CONVERT_DOUBLE_ARG_CHECKED(y, 1);
-  // Returning a smi would not confuse crankshaft as this part of code is only
-  // run if SSE2 was not available, in which case crankshaft is disabled.
-  if (y == 0) return Smi::FromInt(1);  // Returns 1 if exponent is 0.
-  return isolate->heap()->AllocateHeapNumber(power_double_double(x, y));
+  int y_int = static_cast<int>(y);
+  double result;
+  if (y == y_int) {
+    result = power_double_int(x, y_int);  // Returns 1 if exponent is 0.
+  } else  if (y == 0.5) {
+    result = (isinf(x)) ? V8_INFINITY : sqrt(x + 0.0);  // Convert -0 to +0.
+  } else if (y == -0.5) {
+    result = (isinf(x)) ? 0 : 1.0 / sqrt(x + 0.0);  // Convert -0 to +0.
+  } else {
+    result = power_double_double(x, y);
+  }
+  if (isnan(result)) return isolate->heap()->nan_value();
+  return isolate->heap()->AllocateHeapNumber(result);
 }
 
-// Fast version of Math.pow if we know that y is not an integer and
-// y is not -0.5 or 0.5. Used as slowcase from codegen.
+// Fast version of Math.pow if we know that y is not an integer and y is not
+// -0.5 or 0.5.  Used as slow case from fullcodegen.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_pow_cfunction) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 2);
+  isolate->counters()->math_pow()->Increment();
+
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
   CONVERT_DOUBLE_ARG_CHECKED(y, 1);
   if (y == 0) {
     return Smi::FromInt(1);
   } else if (isnan(y) || ((x == 1 || x == -1) && isinf(y))) {

[ulan, 2011/12/07 16:03:04]

This code is almost the same as in power_double_double. Can we reuse it?

     return isolate->heap()->nan_value();
   } else {
     return isolate->heap()->AllocateHeapNumber(pow(x, y));
   }
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_RoundNumber) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
@@ skipping 6126 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags);
   }
 }
 
 
 } }  // namespace v8::internal