Avoid overflow in checking for emulation bytes in rbsp.

Avoid overflow in checking for emulation bytes in rbsp.

Also fixed an arithmetic issue where a 0 0 3 at the end of the rbsp would include the 3 (that's not a legal bitstream anyway, so it probably wasn't a real bug, but it was incorrect).

This maintains the underflow fix from an earlier CL (https://codereview.webrtc.org/1219493004/). The overflow fix is virtually impossible to hit (hence no unit tests), but is there for strict correctness.

BUG=

Committed: https://crrev.com/43e7d3bc150788045b549f4ab94a91095980d059
Cr-Commit-Position: refs/heads/master@{#9581}

[noahric, 2015-07-09 00:46:39]

noahric@chromium.org changed reviewers:
+ pbos@webrtc.org

[noahric, 2015-07-09 00:46:39]

Peter: here's the overflow fix + the arithmetic fix. I know you're less happy
with the readability of the new expression, but I'd feel much better knowing the
code is strictly correct. Thanks!

[pbos-webrtc, 2015-07-09 09:20:08]

lgtm, let's be friends (but please comment)

https://codereview.webrtc.org/1226203002/diff/1/webrtc/modules/rtp_rtcp/sourc...
File webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc (right):

https://codereview.webrtc.org/1226203002/diff/1/webrtc/modules/rtp_rtcp/sourc...
webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc:39: if (byte_length_ - i >= 3
&& sps_[i] == 0 && sps_[i + 1] == 0 &&
Can you put a comment here saying that we check (byte_length_ - i) since i <
byte_length_ there's no risk of overflow? Since we're doing specific things here
to avoid overflow it'd be nice to state them so that it doesn't look like it's
just written in a different style.

[noahric, 2015-07-09 22:05:16]

On 2015/07/09 09:20:08, pbos-webrtc wrote:
> lgtm, let's be friends (but please comment)
> 
>
https://codereview.webrtc.org/1226203002/diff/1/webrtc/modules/rtp_rtcp/sourc...
> File webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc (right):
> 
>
https://codereview.webrtc.org/1226203002/diff/1/webrtc/modules/rtp_rtcp/sourc...
> webrtc/modules/rtp_rtcp/source/h264_sps_parser.cc:39: if (byte_length_ - i >=
3
> && sps_[i] == 0 && sps_[i + 1] == 0 &&
> Can you put a comment here saying that we check (byte_length_ - i) since i <
> byte_length_ there's no risk of overflow? Since we're doing specific things
here
> to avoid overflow it'd be nice to state them so that it doesn't look like it's
> just written in a different style.

Certainly :) I had considered it originally but I wasn't sure what the consensus
was on that type of developer note. But I think it's better to err on the side
of verbosity for edge case stuff like that. Done.

[noahric, 2015-07-09 22:05:57]

The CQ bit was checked by noahric@chromium.org

[noahric, 2015-07-09 22:05:58]

The patchset sent to the CQ was uploaded after l-g-t-m from pbos@webrtc.org
Link to the patchset: https://codereview.webrtc.org/1226203002/#ps20001 (title:
"Added clarifying comment")

[commit-bot: I haz the power, 2015-07-09 22:06:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226203002/20001

[commit-bot: I haz the power, 2015-07-09 22:10:07]

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

[commit-bot: I haz the power, 2015-07-09 22:10:08]

Try jobs failed on following builders:
  presubmit on tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/presubmit/builds/139)

[noahric, 2015-07-09 22:11:35]

noahric@chromium.org changed reviewers:
+ stefan@webrtc.org

[noahric, 2015-07-09 22:11:35]

Stefan, can you take a look and LGTM for owners if it looks ok? Thanks!

[stefan-webrtc, 2015-07-14 12:16:42]

lgtm

[noahric, 2015-07-14 16:34:25]

The CQ bit was checked by noahric@chromium.org

[commit-bot: I haz the power, 2015-07-14 16:34:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1226203002/20001

[commit-bot: I haz the power, 2015-07-14 17:45:07]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-07-14 17:45:17]

Patchset 2 (id:??) landed as
https://crrev.com/43e7d3bc150788045b549f4ab94a91095980d059
Cr-Commit-Position: refs/heads/master@{#9581}