code review 5440113: math/go: added BitCount() to Int.

math/go: added BitCount() to Int.

To count the number of bits set in Int, the BitCount() method was added.
Corresponding bitCount() functions were added to nat.go and arith.go.

The underlying func bitCount(x Word) (n int) uses the Wegner algorithm.
It is not the best algorithm (particularly when there are many 1's),
but it is simple and passes written test cases.

The commented out block of code above corresponds to another
algorithm: variable-precision SWAR algorithm. However, this code did
not pass the test cases.
Perhaps it had something to do with integer overflow?

Regardless, the Wegner algorithm worked well and passes all test
cases added to int_test.go.

The bitCount function should perhaps return uint64 instead to
guard against overflow. But the return variable is set as int
in order to be consistent with the bitLen function and friends.

[davids, 2012-02-01 05:39:14]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go/

[dsymonds, 2012-02-01 06:39:25]

In the words of the sages, "not now". Perhaps after Go 1.


Dave.

[anacrolix, 2014-09-11 18:09:21]

Can this be revisited?

[gobot, 2014-09-11 18:10:44]

Replacing golang-dev with golang-codereviews.

To the author of this CL: 

If you are using 'hg mail -r golang-dev' to mail the CL, use simply 'hg mail'
instead.

If you did not name golang-dev explicitly and it was still added to the CL,
it means your working copy of the repo has a stale codereview.cfg
(or lib/codereview/codereview.cfg).
Please run 'hg sync' to update your client to the most recent codereview.cfg.
If the most recent codereview.cfg has defaultcc set to golang-dev instead of
golang-codereviews, please send a CL correcting it.

Thanks very much.

[iant, 2014-09-12 13:29:10]

On Thu, Sep 11, 2014 at 11:09 AM,  <anacrolix@gmail.com> wrote:
> Can this be revisited?
>
> https://codereview.appspot.com/5440113/

I'm sorry, now you've run into the 1.4 feature freeze.  This could be
revisited after the 1.4 release.

Ian

[gobot, 2014-12-19 05:18:09]

R=close

To the author of this CL:

The Go project has moved to Gerrit Code Review.

If this CL should be continued, please see the latest version of
https://golang.org/doc/contribute.html for instructions on
how to set up Git and the Go project's Gerrit codereview plugin,
and then create a new change with your current code.

If there has been discussion on this CL, please give a link to it
(golang.org/cl/5440113 is best) in the description in your
new CL.

Thanks very much.