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Implements experimental diff with optimized moves calculation to prod…
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…uce only minimal required moves
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@tarbayev
tarbayev authored and Nickolay Tarbayev committed Jul 20, 2018
1 parent f469c34 commit 6e173c2
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag

### Enhancements

- Implemented experimental diff with optimized moves calculation to produce only minimal required moves, enabled by `IGListExperimentOptimizedMoves` option. [Nickolay Tarbayev](https://github.com/tarbayev) [(#1139)](https://github.com/Instagram/IGListKit/pull/1139)

- Add support for UICollectionView's interactive reordering in iOS 9+. Updates include `-[IGListSectionController canMoveItemAtIndex:]` to enable the behavior, `-[IGListSectionController moveObjectFromIndex:toIndex:]` called when items within a section controller were moved through reordering, `-[IGListAdapterDataSource listAdapter:moveObject:from:to]` called when section controllers themselves were reordered (only possible when all section controllers contain exactly 1 object), and `-[IGListUpdatingDelegate moveSectionInCollectionView:fromIndex:toIndex]` to enable custom updaters to conform to the reordering behavior. The update also includes two new examples `ReorderableSectionController` and `ReorderableStackedViewController` to demonstrate how to enable interactive reordering in your client app. [Jared Verdi](https://github.com/jverdi) [(#976)](https://github.com/Instagram/IGListKit/pull/976)

- 5x improvement to diffing performance when result is only inserts or deletes. [Ryan Nystrom](https://github.com/rnystrom) [(tbd)](tbd)
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12 changes: 12 additions & 0 deletions IGListKit.xcodeproj/project.pbxproj
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Expand Up @@ -7,6 +7,10 @@
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Expand Down Expand Up @@ -407,6 +411,8 @@
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Expand Down Expand Up @@ -661,6 +667,7 @@
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Expand Down Expand Up @@ -846,6 +853,7 @@
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Expand Down Expand Up @@ -975,6 +983,7 @@
294AC6311DDE4C19002FCE5D /* IGListDiffResultTests.m */,
88144EE61D870EDC007C7F66 /* IGListDiffSwiftTests.swift */,
88144EE81D870EDC007C7F66 /* IGListDiffTests.m */,
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29DA5CA21EA7C72400113926 /* IGListGenericSectionControllerTests.m */,
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Expand Down Expand Up @@ -1559,6 +1568,7 @@
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298DDA3B1E3B16F800F76F50 /* IGLayoutTestDataSource.m in Sources */,
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Expand Down Expand Up @@ -1681,6 +1691,7 @@
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Expand Down Expand Up @@ -1732,6 +1743,7 @@
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128 changes: 120 additions & 8 deletions Source/Common/IGListDiff.mm
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Expand Up @@ -94,6 +94,105 @@ static void addIndexToCollection(BOOL useIndexPaths, __unsafe_unretained id coll
return paths;
}

// Calculates indexes which require no explicit moves based on a longest increasing indexes set using O(n log n) complexity algorithm
static NSIndexSet *autoMovedIndexes(const vector<IGListRecord> &newResultsArray, NSIndexSet *untouchedIndexes)
{
NSUInteger count = newResultsArray.size();
vector<NSUInteger> prevIndexes(count);
vector<NSUInteger> indexes(count + 1);

NSUInteger length = 0;
for (NSUInteger i = 0; i < count; i++) {
// Binary search for the largest positive j ≤ length
// such that X[M[j]] < X[i]
NSUInteger lo = 1;
NSUInteger hi = length;
NSInteger currentIndex = newResultsArray[i].index;

NSUInteger nextUntouched = [untouchedIndexes indexGreaterThanIndex:i];

if (nextUntouched != NSNotFound && currentIndex > nextUntouched) {
continue;
}

NSUInteger prevUntouched = [untouchedIndexes indexLessThanIndex:i];

if (prevUntouched != NSNotFound && currentIndex < prevUntouched) {
continue;
}

while (lo <= hi) {
auto mid = lo + (hi - lo) / 2;
NSInteger prevIndex = newResultsArray[indexes[mid]].index;
if (prevIndex < currentIndex && (prevUntouched == NSNotFound || prevIndex > prevUntouched)) {
lo = mid + 1;
} else {
hi = mid - 1;
}
}

// After searching, lo is 1 greater than the
// length of the longest prefix of X[i]
auto newLength = lo;

// The predecessor of X[i] is the last index of
// the subsequence of length newLength-1
prevIndexes[i] = indexes[newLength - 1];
indexes[newLength] = i;

if (newLength > length) {
// If we found a subsequence longer than any we've
// found yet, update L
length = newLength;
}
}

// Reconstruct the longest increasing indexes
NSMutableIndexSet *result = [NSMutableIndexSet new];
auto k = indexes[length];
for (NSUInteger i = 0; i < length; i++) {
NSUInteger index = newResultsArray[k].index;

// Ignore inserted entries
if (index != NSNotFound) {
[result addIndex:index];
}
k = prevIndexes[k];
}
return result;
}

class IGListMoveChecker {
public:
virtual bool isMove(const NSInteger oldIndex,
const NSInteger newIndex,
const NSInteger insertOffset,
const NSInteger deleteOffset) {

return (oldIndex - deleteOffset + insertOffset) != newIndex;
}

virtual ~IGListMoveChecker() {}
};

class IGListOptimalMoveChecker : public IGListMoveChecker
{
NSIndexSet *_autoMovedIndexes;

public:
IGListOptimalMoveChecker(const vector<IGListRecord> &newResultsArray, NSIndexSet *untouchedIndexes)
: _autoMovedIndexes(autoMovedIndexes(newResultsArray, untouchedIndexes))
{}

virtual bool isMove(const NSInteger oldIndex,
const NSInteger newIndex,
const NSInteger insertOffset,
const NSInteger deleteOffset) {

return (oldIndex != newIndex) && ![_autoMovedIndexes containsIndex:oldIndex];
}
};

static id IGListDiffing(BOOL returnIndexPaths,
NSInteger fromSection,
NSInteger toSection,
Expand Down Expand Up @@ -245,9 +344,11 @@ static id IGListDiffing(BOOL returnIndexPaths,
}

// track offsets from deleted items to calculate where items have moved
vector<NSInteger> deleteOffsets(oldCount), insertOffsets(newCount);
vector<NSInteger> deleteOffsets(oldCount);
NSInteger runningOffset = 0;

auto untouchedIndexes = [NSMutableIndexSet new];

// iterate old array records checking for deletes
// incremement offset for each delete
for (NSInteger i = 0; i < oldCount; i++) {
Expand All @@ -257,33 +358,42 @@ static id IGListDiffing(BOOL returnIndexPaths,
if (record.index == NSNotFound) {
addIndexToCollection(returnIndexPaths, mDeletes, fromSection, i);
runningOffset++;
} else if (record.index == i) {
[untouchedIndexes addIndex:record.index];
}

addIndexToMap(returnIndexPaths, fromSection, i, oldArray[i], oldMap);
}

// reset and track offsets from inserted items to calculate where items have moved
runningOffset = 0;

aligned_union<0, IGListMoveChecker, IGListOptimalMoveChecker>::type moveCheckerBuf;

IGListMoveChecker *moveChecker = IGListExperimentEnabled(experiments, IGListExperimentOptimizedMoves)
? new (&moveCheckerBuf) IGListOptimalMoveChecker(newResultsArray, untouchedIndexes)
: new (&moveCheckerBuf) IGListMoveChecker();

// offset incremented for each insert
NSInteger insertOffset = 0;

for (NSInteger i = 0; i < newCount; i++) {
insertOffsets[i] = runningOffset;
const IGListRecord record = newResultsArray[i];
const NSInteger oldIndex = record.index;
// add to inserts if the opposing index is NSNotFound
if (record.index == NSNotFound) {
addIndexToCollection(returnIndexPaths, mInserts, toSection, i);
runningOffset++;
insertOffset++;
} else {
// note that an entry can be updated /and/ moved
if (record.entry->updated) {
addIndexToCollection(returnIndexPaths, mUpdates, fromSection, oldIndex);
}

// calculate the offset and determine if there was a move
// if the indexes match, ignore the index
const NSInteger insertOffset = insertOffsets[i];
const NSInteger deleteOffset = deleteOffsets[oldIndex];
if ((oldIndex - deleteOffset + insertOffset) != i) {

if (moveChecker->isMove(oldIndex, i, insertOffset, deleteOffset)) {

// add move from old index to new index
id move;
if (returnIndexPaths) {
NSIndexPath *from = [NSIndexPath indexPathForItem:oldIndex inSection:fromSection];
Expand All @@ -299,6 +409,8 @@ static id IGListDiffing(BOOL returnIndexPaths,
addIndexToMap(returnIndexPaths, toSection, i, newArray[i], newMap);
}

moveChecker->~IGListMoveChecker();

NSCAssert((oldCount + [mInserts count] - [mDeletes count]) == newCount,
@"Sanity check failed applying %li inserts and %lu deletes to old count %lu equaling new count %li",
(long)oldCount, (unsigned long)[mInserts count], (unsigned long)[mDeletes count], (long)newCount);
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2 changes: 2 additions & 0 deletions Source/Common/IGListExperiments.h
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Expand Up @@ -26,6 +26,8 @@ typedef NS_OPTIONS (NSInteger, IGListExperiment) {
IGListExperimentFasterVisibleSectionController = 1 << 4,
/// Test deduping item-level updates.
IGListExperimentDedupeItemUpdates = 1 << 5,
/// Test optimized moves to minimal required number
IGListExperimentOptimizedMoves = 1 << 6,
};

/**
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