Avoid Bigint literals in Dart core library

runtime/lib/bigint.dart

Index: runtime/lib/bigint.dart
diff --git a/runtime/lib/bigint.dart b/runtime/lib/bigint.dart
index af03ea41fd62394b676623b0b59d6b2126c524e9..217b6ed027913af46acc604126dda38121701ef3 100644
--- a/runtime/lib/bigint.dart
+++ b/runtime/lib/bigint.dart
@@ -57,6 +57,10 @@ class _Bigint extends _IntegerImplementation implements int {
   static const int _DIGIT2_BITS = _DIGIT_BITS >> 1;
   static const int _DIGIT2_MASK = (1 << _DIGIT2_BITS) - 1;
 
+  // Bits per 2 digits
+  static const int _TWO_DIGITS_BITS = _DIGIT_BITS << 1;
+  static const int _TWO_DIGITS_MASK = (1 << _TWO_DIGITS_BITS) - 1;

[regis, 2017/07/17 16:45:31]

How is this supposed to work? Do you avoid the creation of a bigint when bigints
are disabled, because the shift will wrap around? A comment explaining these new
constants would be nice.

[alexmarkov, 2017/07/17 20:21:28]

Done.

+
   // Min and max of non bigint values.
   static const int _MIN_INT64 = (-1) << 63;
   static const int _MAX_INT64 = 0x7fffffffffffffff;
@@ -1932,7 +1936,8 @@ class _Montgomery implements _Reduction {
         0xffff; // y == 1/x mod 2^16
     y = (y * (2 - ((xl * y) & 0xffffffff))) & 0xffffffff; // y == 1/x mod 2^32
     var x = (args[_X_HI] << _Bigint._DIGIT_BITS) | xl;
-    y = (y * (2 - ((x * y) & 0xffffffffffffffff))) & 0xffffffffffffffff;
+    y = (y * (2 - ((x * y) & _Bigint._TWO_DIGITS_MASK))) &
+        _Bigint._TWO_DIGITS_MASK;
     // y == 1/x mod _DIGIT_BASE^2
     y = -y; // We really want the negative inverse.
     args[_RHO] = y & _Bigint._DIGIT_MASK;