Harden LinearGradient4fContext

Harden LinearGradient4fContext

Three distinct issues exposed by Fuzzer:

1) truncating the flags to 8 bits may trip the assert in SkToU8

Since clients can pass in any garbage, we cannot assume it fits in 8
bits.  Just static_cast<> instead.

2) vertical gradients with dx == -0.0 don't trigger interval inversion.

For dx < 0 we want reversed intervals.  But, alas, -0.0 < 0 == false
(thanks, Ob^WIEEE 754!).  Use signbit() instead.

3) half closed range checking needs to be inverted for reversed
intervals.

Normally we check for [p0, p1), but for reversed intervals (p1 < p0) we
want to check for [p1, p0), and not (p1, p0].  Adjust the logic
accordingly.

BUG=skia:5647
R=reed@google.com,kjlubick@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2349153004

Committed: https://skia.googlesource.com/skia/+/6d7e4e83035845e87c7972af2e7b635c0a5afbb0

[f(malita), 2016-09-20 01:30:03]

Description was changed from

==========
Harden LinearGradient4fContext

Three distinct issues exposed by Fuzzer:

1) truncating the flags to 8 bits may trip the assert in SkToU8

Since clients can pass in any garbage, we cannot assume it fits in 8
bits.  Just static_cast<> instead.

2) vertical gradients with dx == -0.0 don't trigger interval inversion.

For dx < 0 we want reversed intervals.  But, alas, -0.0 < 0 == false
(thanks, Ob^WIEEE 754!).  Use signbit() instead.

3) half closed range checking needs to be inverted for reversed
intervals.

Normally we check for [p0, p1), but for reversed intervals (p1 < p0) we
want to check for [p1, p0), and not (p1, p0].  Adjust the logic
accordingly.

BUG=skia:5647
R=reed@google.com,kjlubick@google.com
==========

to

==========
Harden LinearGradient4fContext

Three distinct issues exposed by Fuzzer:

1) truncating the flags to 8 bits may trip the assert in SkToU8

Since clients can pass in any garbage, we cannot assume it fits in 8
bits.  Just static_cast<> instead.

2) vertical gradients with dx == -0.0 don't trigger interval inversion.

For dx < 0 we want reversed intervals.  But, alas, -0.0 < 0 == false
(thanks, Ob^WIEEE 754!).  Use signbit() instead.

3) half closed range checking needs to be inverted for reversed
intervals.

Normally we check for [p0, p1), but for reversed intervals (p1 < p0) we
want to check for [p1, p0), and not (p1, p0].  Adjust the logic
accordingly.

BUG=skia:5647
R=reed@google.com,kjlubick@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2349153004
==========

[f(malita), 2016-09-20 01:33:54]

The CQ bit was checked by fmalita@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-09-20 01:34:00]

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, 2016-09-20 02:10:19]

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

[commit-bot: I haz the power, 2016-09-20 02:10:19]

Dry run: This issue passed the CQ dry run.

[kjlubick, 2016-09-20 11:43:32]

lgtm

[f(malita), 2016-09-20 13:53:58]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2016-09-20 13:54:03]

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, 2016-09-20 13:55:17]

Description was changed from

==========
Harden LinearGradient4fContext

Three distinct issues exposed by Fuzzer:

1) truncating the flags to 8 bits may trip the assert in SkToU8

Since clients can pass in any garbage, we cannot assume it fits in 8
bits.  Just static_cast<> instead.

2) vertical gradients with dx == -0.0 don't trigger interval inversion.

For dx < 0 we want reversed intervals.  But, alas, -0.0 < 0 == false
(thanks, Ob^WIEEE 754!).  Use signbit() instead.

3) half closed range checking needs to be inverted for reversed
intervals.

Normally we check for [p0, p1), but for reversed intervals (p1 < p0) we
want to check for [p1, p0), and not (p1, p0].  Adjust the logic
accordingly.

BUG=skia:5647
R=reed@google.com,kjlubick@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2349153004
==========

to

==========
Harden LinearGradient4fContext

Three distinct issues exposed by Fuzzer:

1) truncating the flags to 8 bits may trip the assert in SkToU8

Since clients can pass in any garbage, we cannot assume it fits in 8
bits.  Just static_cast<> instead.

2) vertical gradients with dx == -0.0 don't trigger interval inversion.

For dx < 0 we want reversed intervals.  But, alas, -0.0 < 0 == false
(thanks, Ob^WIEEE 754!).  Use signbit() instead.

3) half closed range checking needs to be inverted for reversed
intervals.

Normally we check for [p0, p1), but for reversed intervals (p1 < p0) we
want to check for [p1, p0), and not (p1, p0].  Adjust the logic
accordingly.

BUG=skia:5647
R=reed@google.com,kjlubick@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2349153004

Committed:
https://skia.googlesource.com/skia/+/6d7e4e83035845e87c7972af2e7b635c0a5afbb0
==========

[commit-bot: I haz the power, 2016-09-20 13:55:18]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/6d7e4e83035845e87c7972af2e7b635c0a5afbb0