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Bug 1554075 - Add fast path for IntervalSet::operator-= for removing a range that touches the front of a length 1 IntervalSet. r=jya

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Twitch usually evicts data at the start of its buffered range, so handling this
case specially means we'll avoid the expensive general case.

Differential Revision: https://phabricator.services.mozilla.com/D33874

--HG--
extra : moz-landing-system : lando
This commit is contained in:
Chris Pearce 2019-06-11 05:09:43 +00:00
parent 6fd2c596b2
commit ab6c396d61
1 changed files with 22 additions and 2 deletions
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24
dom/media/Intervals.h
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@ -225,6 +225,12 @@ class Interval {
(aOther.mStart - aOther.mFuzz <= mEnd + mFuzz);
}
// Returns true if the two intervals intersect with this being on the right
// of aOther, ignoring fuzz.
bool TouchesOnRightStrict(const SelfType& aOther) const {
return aOther.mStart <= mStart && mStart <= aOther.mEnd;
}
T mStart;
T mEnd;
T mFuzz;
@ -383,12 +389,26 @@ class IntervalSet {
}
// Excludes an interval from an IntervalSet.
// This is done by inverting aInterval within the bounds of mIntervals
// and then doing the intersection.
SelfType& operator-=(const ElemType& aInterval) {
if (aInterval.IsEmpty() || mIntervals.IsEmpty()) {
return *this;
}
if (mIntervals.Length() == 1 &&
mIntervals[0].TouchesOnRightStrict(aInterval)) {
// Fast path when we're removing from the front of a set with a
// single interval. This is common for the buffered time ranges
// we see on Twitch.
if (aInterval.mEnd >= mIntervals[0].mEnd) {
mIntervals.RemoveElementAt(0);
} else {
mIntervals[0].mStart = aInterval.mEnd;
mIntervals[0].mFuzz = std::max(mIntervals[0].mFuzz, aInterval.mFuzz);
}
return *this;
}
// General case performed by inverting aInterval within the bounds of
// mIntervals and then doing the intersection.
T firstEnd = std::max(mIntervals[0].mStart, aInterval.mStart);
T secondStart = std::min(mIntervals.LastElement().mEnd, aInterval.mEnd);
ElemType startInterval(mIntervals[0].mStart, firstEnd);