Artikel getaggt mit Binary

Poignant: Xml meets Huffman

There’s a spec at the w3c about compressing (XML) named “Efficient XML Interchange” Format taking into account the grammar and likelihood of atoms within the document. They indeed use something similar the the Huffman Coding.

The results are quite impressive – nice charts!

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Binary Search NSArray

Though CFArray comes with binary search capability, NSArray does not – at least not within the iPhone SDK. The indexOfObject:inSortedRange:options:usingComparator: can’t be found.

Plus the CFArrayBSearchValues doesn’t tell you whether the key actually is part of the list or not. That’s what the Java JDK does, so let’s implement some category methods

-(NSInteger)binarySearch:(id)key;
-(NSInteger)binarySearch:(id)key usingSelector:(SEL)comparator;
-(NSInteger)binarySearch:(id)key usingSelector:(SEL)comparator inRange:(NSRange)range;
-(NSInteger)binarySearch:(id)key usingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context;
-(NSInteger)binarySearch:(id)key usingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context inRange:(NSRange)range;
-(NSInteger)binarySearch:(id)key usingDescriptors:(NSArray *)sortDescriptors;
-(NSInteger)binarySearch:(id)key usingDescriptors:(NSArray *)sortDescriptors inRange:(NSRange)range;

ourselves, like

-(NSInteger)binarySearch:(id)key usingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context inRange:(NSRange)range
{
    NSLogD(@"[NSArray(MroBinarySearch) binarySearch:%@ usingFunction:]", key);
    if(self.count == 0 || key == nil || comparator == NULL)
        return [self binarySearch:key usingSelector:nil inRange:range];
 
//	check overflow?
    NSInteger min = range.location;
    NSInteger max = range.location + range.length - 1;
 
    while (min < = max)
    {
        // http://googleresearch.blogspot.com/2006/06/extra-extra-read-all-about-it-nearly.html
        const NSInteger mid = min + (max - min) / 2;
        switch (comparator(key, [self objectAtIndex:mid], context))
        {
            case NSOrderedSame:
                return mid;
            case NSOrderedDescending:
                min = mid + 1;
                break;
            case NSOrderedAscending:
                max = mid - 1;
                break;
        }
    }
    return -(min + 1);
}

See the full interface + implementation + testcase without html encoding dirt at github.

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CocoaTouch, CoreData and binary String Search

The query optimiser for NSPredicate queries ontop CoreData/SQLite on the iPhone is a bit rudimentary (cough) and so I had to optimise myself to get binary-search enabled quick results:

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