Prevent deopt when assigning double values to typed arrays

src/conversions-inl.h

Index: src/conversions-inl.h
diff --git a/src/conversions-inl.h b/src/conversions-inl.h
index cb7dbf88d2a32d7f132fcc5e9e76da60102b461e..eed64cd26f89668b86122c4963a261a2947d9475 100644
--- a/src/conversions-inl.h
+++ b/src/conversions-inl.h
@@ -1,4 +1,4 @@
-// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// 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:
@@ -77,6 +77,20 @@ static inline double DoubleToInteger(double x) {
 }
 
 
+uint8_t ClampToUInt8(double double_value) {
+  if (!(double_value > 0)) {
+    // NaN and less than zero clamp to zero.
+    return 0;
+  } else if (double_value > 255) {
+    // Greater than 255 clamp to 255.
+    return 255;
+  } else {
+    // Other doubles are rounded to the nearest integer.
+    return static_cast<uint8_t>(double_value + 0.5);
+  }
+}
+
+
 int32_t NumberToInt32(Object* number) {
   if (number->IsSmi()) return Smi::cast(number)->value();
   return DoubleToInt32(number->Number());
@@ -89,6 +103,28 @@ uint32_t NumberToUint32(Object* number) {
 }
 
 
+uint8_t NumberToClampedUInt8(Object* number)
+{
+  if (number->IsSmi()) {
+    int32_t value = Smi::cast(number)->value();
+    if (value < 0) {
+      return 0;
+    } else if (value > 255) {
+      return 255;
+    } else {
+      return static_cast<uint8_t>(value);
+    }
+  } else if (number->IsHeapNumber()) {
+    return ClampToUInt8(number->Number());
+  } else {
+    // Clamp undefined to zero (default). All other types have been
+    // converted to a number type further up in the call chain.
+    ASSERT(number->IsUndefined());
+    return 0;
+  }
+}
+
+
 int32_t DoubleToInt32(double x) {
   int32_t i = FastD2I(x);
   if (FastI2D(i) == x) return i;