Clamp rgba(...) alpha value in the CSS fast-path parser

Clamp rgba(...) alpha value in the CSS fast-path parser

The general CSS parser will clamp the alpha value to the [0, 1] range,
while the fast-path parser does not. This means that large alpha values
will result in overflow in the cast to int, yielding the wrong color
value.
Add a clamp to the [0, 1] range before converting to the [0, 256) range
and converting to int. Because negative values are handled separately,
we only need to apply the clamp for the range above zero.

BUG=675158
Committed: https://crrev.com/6c6634508a1438f66057dc414af8171be9602e7c
Cr-Commit-Position: refs/heads/master@{#440374}

[fs, 2016-12-20 15:09:54]

The CQ bit was checked by fs@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2016-12-20 15:10:09]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-20 18:15:08]

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

[commit-bot: I haz the power, 2016-12-20 18:15:08]

Dry run: Try jobs failed on following builders:
  win_chromium_rel_ng on master.tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[fs, 2016-12-20 18:47:29]

fs@opera.com changed reviewers:
+ alancutter@chromium.org

[alancutter (OOO until 2018), 2016-12-20 23:31:24]

https://codereview.chromium.org/2588293004/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp (right):

https://codereview.chromium.org/2588293004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp:380: :
static_cast<int>(std::min(alpha, 1.0) * nextafter(256.0, 0.0));
Instead of static_cast can we use clampTo<int>?

[fs, 2016-12-21 08:53:00]

https://codereview.chromium.org/2588293004/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp (right):

https://codereview.chromium.org/2588293004/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp:380: :
static_cast<int>(std::min(alpha, 1.0) * nextafter(256.0, 0.0));
On 2016/12/20 at 23:31:24, alancutter wrote:
> Instead of static_cast can we use clampTo<int>?

We can, but it would be a waste of perfectly good CPU cycles. (Converting from a
double in [0, 256) to an int cannot overflow the int, so the roughly handful of
extra instructions will not do anything.)

[alancutter (OOO until 2018), 2016-12-21 23:20:03]

lgtm

[fs, 2016-12-22 08:39:30]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2016-12-22 08:39:41]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-22 10:10:53]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1482395970698460, "parent_rev":
"0615a140ba128d5fd00903972c65c3e33a22cac5", "commit_rev":
"6217412035b2fba5c1dc0952851ee26739fe7030"}

[commit-bot: I haz the power, 2016-12-22 10:11:20]

Description was changed from

==========
Clamp rgba(...) alpha value in the CSS fast-path parser

The general CSS parser will clamp the alpha value to the [0, 1] range,
while the fast-path parser does not. This means that large alpha values
will result in overflow in the cast to int, yielding the wrong color
value.
Add a clamp to the [0, 1] range before converting to the [0, 256) range
and converting to int. Because negative values are handled separately,
we only need to apply the clamp for the range above zero.

BUG=675158
==========

to

==========
Clamp rgba(...) alpha value in the CSS fast-path parser

The general CSS parser will clamp the alpha value to the [0, 1] range,
while the fast-path parser does not. This means that large alpha values
will result in overflow in the cast to int, yielding the wrong color
value.
Add a clamp to the [0, 1] range before converting to the [0, 256) range
and converting to int. Because negative values are handled separately,
we only need to apply the clamp for the range above zero.

BUG=675158

Review-Url: https://codereview.chromium.org/2588293004
==========

[commit-bot: I haz the power, 2016-12-22 10:11:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-22 10:13:46]

Description was changed from

==========
Clamp rgba(...) alpha value in the CSS fast-path parser

The general CSS parser will clamp the alpha value to the [0, 1] range,
while the fast-path parser does not. This means that large alpha values
will result in overflow in the cast to int, yielding the wrong color
value.
Add a clamp to the [0, 1] range before converting to the [0, 256) range
and converting to int. Because negative values are handled separately,
we only need to apply the clamp for the range above zero.

BUG=675158

Review-Url: https://codereview.chromium.org/2588293004
==========

to

==========
Clamp rgba(...) alpha value in the CSS fast-path parser

The general CSS parser will clamp the alpha value to the [0, 1] range,
while the fast-path parser does not. This means that large alpha values
will result in overflow in the cast to int, yielding the wrong color
value.
Add a clamp to the [0, 1] range before converting to the [0, 256) range
and converting to int. Because negative values are handled separately,
we only need to apply the clamp for the range above zero.

BUG=675158

Committed: https://crrev.com/6c6634508a1438f66057dc414af8171be9602e7c
Cr-Commit-Position: refs/heads/master@{#440374}
==========

[commit-bot: I haz the power, 2016-12-22 10:13:47]

Patchset 1 (id:??) landed as
https://crrev.com/6c6634508a1438f66057dc414af8171be9602e7c
Cr-Commit-Position: refs/heads/master@{#440374}