Fix code that left shifts a negative value. This has undefined behavior.

Fix code that left shifts a negative value.  This has undefined behavior.

Patched from internal cl/107515669 by rtrieu and added comments.

BUG=skia:2481
Committed: https://skia.googlesource.com/skia/+/0b2a18922146c6134515d42baf5935b71bba03c3

[dogben, 2015-11-11 02:34:05]

The CQ bit was checked by benjaminwagner@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-11-11 02:34:12]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1439483002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1439483002/1

[commit-bot: I haz the power, 2015-11-11 02:46:22]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-11 02:46:22]

Dry run: This issue passed the CQ dry run.

[dogben, 2015-11-11 02:52:39]

benjaminwagner@google.com changed reviewers:
+ mtklein@google.com, reed@google.com

[dogben, 2015-11-11 02:52:39]

Not sure if this change fixed ClampRangeTest or even if the CQ dry run runs with
the correct config to reproduce skia:2481.

[reed1, 2015-11-11 04:20:49]

If we really need those casts in SkFixed.h, I think we should add a comment to
each explaining why. I find it a little odd as a reader, since we are casting a
signed value to unsigned only to then return it as a signed value. I understand
(I think) the argument about C not defining that operation, but I would still
vote for a comment to that effect.

[reed1, 2015-11-11 04:20:51]

If we really need those casts in SkFixed.h, I think we should add a comment to
each explaining why. I find it a little odd as a reader, since we are casting a
signed value to unsigned only to then return it as a signed value. I understand
(I think) the argument about C not defining that operation, but I would still
vote for a comment to that effect.

[dogben, 2015-11-11 15:17:55]

Description was changed from

==========
Fix code that left shifts a negative value.  This has undefined behavior.

Patched from internal cl/107515669 by rtrieu.

BUG=skia:2481
==========

to

==========
Fix code that left shifts a negative value.  This has undefined behavior.

Patched from internal cl/107515669 by rtrieu and added comments.

BUG=skia:2481
==========

[dogben, 2015-11-11 15:18:07]

On 2015/11/11 at 04:20:51, reed wrote:
> If we really need those casts in SkFixed.h, I think we should add a comment to
each explaining why. I find it a little odd as a reader, since we are casting a
signed value to unsigned only to then return it as a signed value. I understand
(I think) the argument about C not defining that operation, but I would still
vote for a comment to that effect.

Done.

[reed1, 2015-11-11 15:40:51]

lgtm

[dogben, 2015-11-11 16:34:12]

The CQ bit was checked by benjaminwagner@google.com

[commit-bot: I haz the power, 2015-11-11 16:34:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1439483002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1439483002/20001

[commit-bot: I haz the power, 2015-11-11 16:46:39]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/0b2a18922146c6134515d42baf5935b71bba03c3