Add 'fixnum' library to utils/

lib/fixnum/intx.dart

Index: lib/fixnum/intx.dart
diff --git a/lib/fixnum/intx.dart b/lib/fixnum/intx.dart
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+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/**
+ * A fixed-precision integer.
+ */
+interface intx extends Comparable, Hashable {
+
+  // Arithmetic operations.
+  intx operator +(other);
+  intx operator -(other);
+  // The unary '-' operator.  Note that -MIN_VALUE will be equal
+  // to MIN_VALUE due to overflow.
+  intx operator negate();
+  intx operator *(other);
+  intx operator %(other);
+  // Truncating division.
+  intx operator ~/(other);
+  intx remainder(other);
+
+  // Note: no / operator
+
+  // Bit-operations.
+  intx operator &(other);
+  intx operator |(other);
+  intx operator ^(other);
+  intx operator ~();
+  intx operator <<(int shiftAmount);
+  intx operator >>(int shiftAmount);
+  intx shiftRightUnsigned(int shiftAmount);
+
+  // Relational operations, may be applied to intx or int.
+  int compareTo(Comparable other);
+  bool operator ==(other);
+  bool operator <(other);
+  bool operator <=(other);
+  bool operator >(other);
+  bool operator >=(other);
+
+  // Testers.
+  bool isEven();
+  bool isMaxValue();
+  bool isMinValue();
+  bool isNegative();
+  bool isOdd();
+  bool isZero();
+
+  int hashCode();
+
+  intx abs();
+
+  /**
+   * Returns the number of leading zeros in this [intx] as an [int]
+   * between 0 and 64.
+   */
+  int numberOfLeadingZeros();
+
+  /**
+   * Returns the number of trailing zeros in this [intx] as an [int]
+   * between 0 and 64.
+   */
+  int numberOfTrailingZeros();
+
+  /**
+   * Converts this [intx] to a [List] of [int], starting with the least
+   * significant byte.
+   */
+  List<int> toBytes();
+
+  /**
+   * Converts this [intx] to an [int].  On some platforms, inputs with large
+   * absolute values (i.e., > 2^52) may lose some of their low bits.
+   */
+  int toInt();
+
+  /**
+   * Converts an [intx] to 32 bits.  Narrower values are sign extended and
+   * wider values have their high bits truncated.
+   */
+  int32 toInt32();
+
+  /**
+   * Converts an [intx] to 64 bits.
+   */
+  int64 toInt64();
+
+  /**
+   * Returns the value of this [intx] as a decimal [String].
+   */
+  String toString();
+
+  /**
+   * Returns the value of this [intx] as a hexadecimal [String].
+   */
+  String toHexString();
+
+  /**
+   * Returns the value of this [intx] as a [String] in the given radix.
+   * [radix] must be an integer between 2 and 16, inclusive.
+   */
+  String toRadixString(int radix);
+}