Make ASWeakSet and NSArray+Diffing public, add support for large arrays (#2078)

AsyncDisplayKit/Details/NSArray+Diffing.m

@@ -0,0 +1,103 @@
+//
+//  NSArray+Diffing.m
+//  AsyncDisplayKit
+//
+//  Created by Levi McCallum on 1/29/16.
+//
+//  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+//
+
+#import "NSArray+Diffing.h"
+#import "ASAssert.h"
+
+@implementation NSArray (Diffing)
+
+- (void)asdk_diffWithArray:(NSArray *)array insertions:(NSIndexSet **)insertions deletions:(NSIndexSet **)deletions
+{
+  [self asdk_diffWithArray:array insertions:insertions deletions:deletions compareBlock:^BOOL(id lhs, id rhs) {
+    return [lhs isEqual:rhs];
+  }];
+}
+
+- (void)asdk_diffWithArray:(NSArray *)array insertions:(NSIndexSet **)insertions deletions:(NSIndexSet **)deletions compareBlock:(BOOL (^)(id lhs, id rhs))comparison
+{
+  NSAssert(comparison != nil, @"Comparison block is required");
+  NSIndexSet *commonIndexes = [self _asdk_commonIndexesWithArray:array compareBlock:comparison];
+  
+  if (insertions) {
+    NSArray *commonObjects = [self objectsAtIndexes:commonIndexes];
+    NSMutableIndexSet *insertionIndexes = [NSMutableIndexSet indexSet];
+    for (NSInteger i = 0, j = 0; i < commonObjects.count || j < array.count;) {
+      if (i < commonObjects.count && j < array.count && comparison(commonObjects[i], array[j])) {
+        i++; j++;
+      } else {
+        [insertionIndexes addIndex:j];
+        j++;
+      }
+    }
+    *insertions = insertionIndexes;
+  }
+  
+  if (deletions) {
+    NSMutableIndexSet *deletionIndexes = [NSMutableIndexSet indexSet];
+    for (NSInteger i = 0; i < self.count; i++) {
+      if (![commonIndexes containsIndex:i]) {
+        [deletionIndexes addIndex:i];
+      }
+    }
+    *deletions = deletionIndexes;
+  }
+}
+
+- (NSIndexSet *)_asdk_commonIndexesWithArray:(NSArray *)array compareBlock:(BOOL (^)(id lhs, id rhs))comparison
+{
+  NSAssert(comparison != nil, @"Comparison block is required");
+  
+  NSInteger selfCount = self.count;
+  NSInteger arrayCount = array.count;
+  
+  // Allocate the diff map in the heap so we don't blow the stack for large arrays.
+  NSInteger (*lengths)[arrayCount+1] = NULL;
+  size_t lengthsSize = ((selfCount+1) * sizeof(*lengths));
+  // Would rather use initWithCapacity: to skip the zeroing, but TECHNICALLY
+  // `mutableBytes` is only guaranteed to be non-NULL if the data object has a non-zero length.
+  NS_VALID_UNTIL_END_OF_SCOPE NSMutableData *lengthsData = [[NSMutableData alloc] initWithLength:lengthsSize];
+  lengths = lengthsData.mutableBytes;
+  if (lengths == NULL) {
+    ASDisplayNodeFailAssert(@"Failed to allocate memory for diffing with size %tu", lengthsSize);
+    return nil;
+  }
+  
+  for (NSInteger i = 0; i <= selfCount; i++) {
+    id selfObj = i > 0 ? self[i-1] : nil;
+    for (NSInteger j = 0; j <= arrayCount; j++) {
+      if (i == 0 || j == 0) {
+        lengths[i][j] = 0;
+      } else if (comparison(selfObj, array[j-1])) {
+        lengths[i][j] = 1 + lengths[i-1][j-1];
+      } else {
+        lengths[i][j] = MAX(lengths[i-1][j], lengths[i][j-1]);
+      }
+    }
+  }
+  
+  NSMutableIndexSet *common = [NSMutableIndexSet indexSet];
+  NSInteger i = selfCount, j = arrayCount;
+  while(i > 0 && j > 0) {
+    if (comparison(self[i-1], array[j-1])) {
+      [common addIndex:(i-1)];
+      i--; j--;
+    } else if (lengths[i-1][j] > lengths[i][j-1]) {
+      i--;
+    } else {
+      j--;
+    }
+  }
+  
+  return common;
+}
+
+@end