[runtime] Add PositiveNumberToUint32 helper to avoid double to uint roundtrip

src/conversions-inl.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CONVERSIONS_INL_H_
 #define V8_CONVERSIONS_INL_H_
 
 #include <float.h>         // Required for DBL_MAX and on Win32 for finite()
 #include <limits.h>        // Required for INT_MAX etc.
 #include <stdarg.h>
@@ skipping 110 matching lines @@
   return !IsMinusZero(value) && value >= 0 && value <= kMaxUInt32 &&
          value == FastUI2D(FastD2UI(value));
 }
 
 
 int32_t NumberToInt32(Object* number) {
   if (number->IsSmi()) return Smi::cast(number)->value();
   return DoubleToInt32(number->Number());
 }
 
-
 uint32_t NumberToUint32(Object* number) {
   if (number->IsSmi()) return Smi::cast(number)->value();
   return DoubleToUint32(number->Number());
 }
 
+uint32_t PositiveNumberToUint32(Object* number) {
+  if (number->IsSmi()) {
+    int value = Smi::cast(number)->value();
+    if (value <= 0) return 0;
+    return value;
+  }
+  DCHECK(number->IsHeapNumber());
+  double value = number->Number();
+  // Catch all values smaller than 1 and use the double-negation trick for NANs.
+  if (!(value >= 1)) return 0;
+  uint32_t max = std::numeric_limits<uint32_t>::max();
+  if (value < max) return static_cast<uint32_t>(value);
+  return max;
+}
+
 int64_t NumberToInt64(Object* number) {
   if (number->IsSmi()) return Smi::cast(number)->value();
   return static_cast<int64_t>(number->Number());
 }
 
 bool TryNumberToSize(Object* number, size_t* result) {
   // Do not create handles in this function! Don't use SealHandleScope because
   // the function can be used concurrently.
   if (number->IsSmi()) {
     int value = Smi::cast(number)->value();
@@ skipping 623 matching lines @@
   buffer[buffer_pos] = '\0';
 
   double converted = Strtod(Vector<const char>(buffer, buffer_pos), exponent);
   return (sign == NEGATIVE) ? -converted : converted;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CONVERSIONS_INL_H_