Esoteric bit operations.

runtime/lib/integers.dart

 // 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.
 
 // TODO(srdjan): fix limitations.
 // - shift amount must be a Smi.
 class _IntegerImplementation {
   factory _IntegerImplementation._uninstantiable() {
     throw new UnsupportedError(
         "_IntegerImplementation can only be allocated by the VM");
@@ skipping 77 matching lines @@
   bool _equalToInteger(int other) native "Integer_equalToInteger";
   int abs() {
     return this < 0 ? -this : this;
   }
   bool get isEven => ((this & 1) == 0);
   bool get isOdd => !isEven;
   bool get isNaN => false;
   bool get isNegative => this < 0;
   bool get isInfinite => false;
 
+  int toUnsigned(int width) {
+    return this & ((1 << width) - 1);
+  }
+
+  int toSigned(int width) {
+    int signMask = 1 << (width - 1);
+    return (this & (signMask - 1)) - (this & signMask);

[Lasse Reichstein Nielsen, 2013/09/06 12:40:11]

Clever. I don't see a good way to document why this works, so I guess it'll just
have to be "because it works". :)

[sra1, 2013/09/06 22:11:57]

I'll give it a shot.

+  }
+
   int compareTo(num other) {
     final int EQUAL = 0, LESS = -1, GREATER = 1;
     if (other is double) {
       // TODO(floitsch): the following locals should be 'const'.
       int MAX_EXACT_INT_TO_DOUBLE = 9007199254740992;  // 2^53.
       int MIN_EXACT_INT_TO_DOUBLE = -MAX_EXACT_INT_TO_DOUBLE;
       double d = other;
       if (d.isInfinite) {
         return d == double.NEGATIVE_INFINITY ? GREATER : LESS;
       }
@@ skipping 97 matching lines @@
 
 class _Smi extends _IntegerImplementation implements int {
   factory _Smi._uninstantiable() {
     throw new UnsupportedError(
         "_Smi can only be allocated by the VM");
   }
   int get hashCode {
     return this;
   }
   int operator ~() native "Smi_bitNegate";
+  int get bitLength native "Smi_bitLength";
+
   int _shrFromInt(int other) native "Smi_shrFromInt";
   int _shlFromInt(int other) native "Smi_shlFromInt";
 
   String toString() {
     if (this == 0) return "0";
     var reversed = new List();
     var val = this < 0 ? -this : this;
     while (val > 0) {
       reversed.add((val % 10) + 0x30);
       val = val ~/ 10;
@@ skipping 20 matching lines @@
 // Represents integers that cannot be represented by Smi but fit into 64bits.
 class _Mint extends _IntegerImplementation implements int {
   factory _Mint._uninstantiable() {
     throw new UnsupportedError(
         "_Mint can only be allocated by the VM");
   }
   int get hashCode {
     return this;
   }
   int operator ~() native "Mint_bitNegate";
+  int get bitLength native "Mint_bitLength";
 
   // Shift by mint exceeds range that can be handled by the VM.
   int _shrFromInt(int other) {
     if (other < 0) {
       return -1;
     } else {
       return 0;
     }
   }
   int _shlFromInt(int other) native "Mint_shlFromInt";
 }
 
 // A number that can be represented as Smi or Mint will never be represented as
 // Bigint.
 class _Bigint extends _IntegerImplementation implements int {
   factory _Bigint._uninstantiable() {
     throw new UnsupportedError(
         "_Bigint can only be allocated by the VM");
   }
   int get hashCode {
     return this;
   }
   int operator ~() native "Bigint_bitNegate";
+  int get bitLength native "Bigint_bitLength";
 
   // Shift by bigint exceeds range that can be handled by the VM.
   int _shrFromInt(int other) {
     if (other < 0) {
       return -1;
     } else {
       return 0;
     }
   }
   int _shlFromInt(int other) native "Bigint_shlFromInt";
 
   int pow(int exponent) {
     throw "Bigint.pow not implemented";
   }
 }