Option to truncate integers to 64 bits, part 1 (core VM changes)

runtime/lib/double.cc

Index: runtime/lib/double.cc
diff --git a/runtime/lib/double.cc b/runtime/lib/double.cc
index 813002445b1cb00c566f19e418bc429e9691e81d..8a8c23797339cc81494141ebbd9f9fa029cc6768 100644
--- a/runtime/lib/double.cc
+++ b/runtime/lib/double.cc
@@ -79,6 +79,19 @@ static RawInteger* DoubleToInteger(double val, const char* error_msg) {
     args.SetAt(0, String::Handle(String::New(error_msg)));
     Exceptions::ThrowByType(Exceptions::kUnsupported, args);
   }
+  if (FLAG_truncate_ints_to_64_bits) {
+    // TODO(alexmarkov): decide on the double-to-integer conversion semantics
+    // in truncating mode.

[regis, 2017/07/07 20:10:29]

Something to discuss with the API people. You could pass a bool here indicating
whether to throw or to use min/max. I think it is safer to throw.

[alexmarkov, 2017/07/07 20:46:38]

Acknowledged.

+    int64_t ival = 0;
+    if (val <= static_cast<double>(kMinInt64)) {
+      ival = kMinInt64;
+    } else if (val >= static_cast<double>(kMaxInt64)) {
+      ival = kMaxInt64;
+    } else {  // representable in int64_t

[regis, 2017/07/07 20:10:29]

The convention is to use a capital letter and a period:
// Representable as int64_t.

[alexmarkov, 2017/07/07 20:46:38]

Done.

+      ival = static_cast<int64_t>(val);
+    }
+    return Integer::New(ival);
+  }
   if ((-1.0 < val) && (val < 1.0)) {
     return Smi::New(0);
   }