Esoteric bit operations.

tests/corelib/bit_twiddling_test.dart

Index: tests/corelib/bit_twiddling_test.dart
diff --git a/tests/corelib/bit_twiddling_test.dart b/tests/corelib/bit_twiddling_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..7cf7e4cf786c80e57bc37ef5f231cb2cdbd8510c
--- /dev/null
+++ b/tests/corelib/bit_twiddling_test.dart
@@ -0,0 +1,93 @@
+// Copyright (c) 2013, 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.
+// Testing Bigints.
+
+library bit_twiddling_test;
+import "package:expect/expect.dart";
+
+
+bool haveBigints() {
+  return 100000000000000000000 + 1 != 100000000000000000000;
+}
+
+testBitLength() {
+  check(int i, width) {
+    Expect.equals(width, i.bitLength, '$i.bitLength ==  $width');
+    Expect.equals(width, (-i-1).bitLength, '(~$i).bitLength == $width');

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

Why -i-1 instead of ~i here? Is it dart2js consideration?

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

Yes, added comment.

+  }
+
+  check(0, 0);
+  check(1, 1);
+  check(2, 2);
+  check(3, 2);
+  check(4, 3);
+  check(5, 3);
+  check(6, 3);
+  check(7, 3);
+  check(8, 4);
+  check(127, 7);
+  check(128, 8);
+  check(129, 8);
+  check(2147483646, 31);
+  check(2147483647, 31);
+  check(2147483648, 32);
+  check(2147483649, 32);
+  check(4294967295, 32);
+  check(4294967296, 33);
+  check(0xffffffffff, 40);
+  check(0xfffffffffff, 44);
+  check(0xffffffffffff, 48);
+  check(0x1000000000000, 49);
+  check(0x1000000000001, 49);
+  check(0x1ffffffffffff, 49);
+  check(0x2000000000000, 50);
+  check(0x2000000000001, 50);
+
+  if (haveBigints()) {
+    check(0xffffffffffffff, 56);
+    check(0xffffffffffffffff, 64);
+    check(0xffffffffffffffffff, 72);
+    check(0x1000000000000000000, 73);
+    check(0x1000000000000000001, 73);
+
+
+    check(0xfffffffffffffffffffffffffffffffffffffe, 152);
+    check(0xffffffffffffffffffffffffffffffffffffff, 152);
+    check(0x100000000000000000000000000000000000000, 153);
+    check(0x100000000000000000000000000000000000001, 153);
+
+  }
+}
+
+testConversions() {
+  checkU(src, width, expected) {
+    Expect.equals(expected, src.toUnsigned(width));
+  }
+  checkS(src, width, expected) {
+    Expect.equals(expected, src.toSigned(width),
+        '$src.toSigned($width) == $expected');
+  }
+  checkU(1, 8, 1);
+  checkU(0xff, 8, 0xff);

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

There is no truncating test, and not unsigned->signed test.
How about
  checkU(0xffff, 8, 0xff);
  checkU(-1, 8, 0xff);
Then I prefer to test around known pain points: 31 bit and 32 bit numbers:
  checkU(0x7fffffff, 30, 0x3fffffff);
  checkU(0x7fffffff, 31, 0x7fffffff);
  checkU(0x7fffffff, 32, 0x7fffffff);
  checkU(0x80000000, 30, 0);
  checkU(0x80000000, 31, 0);
  checkU(0x80000000, 32, 0x80000000);
  checkU(0xffffffff, 30, 0x3fffffff);
  checkU(0xffffffff, 31, 0x7fffffff);
  checkU(0xffffffff, 32, 0xffffffff);
  checkU(0x100000000, 30, 0);
  checkU(0x100000000, 31, 0);
  checkU(0x100000000, 32, 0);
  checkU(0x1ffffffff, 30, 0x3fffffff);
  checkU(0x1ffffffff, 31, 0x7fffffff);
  checkU(0x1ffffffff, 32, 0xffffffff);
  

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

Done.

+  checkU(0xffffffff, 32, 0xffffffff);
+
+  checkU( 1, 0, 0);
+  checkU( 0, 0, 0);
+  checkU(-1, 0, 0);
+
+  checkS(0xff, 8, -1);
+  checkS(128, 8, -128);
+  checkS(0x80000000, 32, -2147483648);

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

Similar truncating tests for signed:
  checkS(-1, 3, -1);
  checkS(-0x101, 8, 0);
Maybe some edge cases too.

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

Done.

+
+  checkS(-1, 1, -1);
+  checkS( 0, 1,  0);
+  checkS( 1, 1, -1);
+  checkS( 2, 1,  0);
+  checkS( 3, 1, -1);
+}
+
+main() {
+  testBitLength();
+  testConversions();
+}