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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.
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// Burton Computer Corporation
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package org.javimmutable.collections.array;

import org.javimmutable.collections.Cursorable;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Indexed;
import org.javimmutable.collections.InvariantCheckable;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.SplitableIterable;
import org.javimmutable.collections.common.MutableDelta;

import javax.annotation.concurrent.Immutable;

@Immutable
public abstract class TrieNode
    implements Cursorable>,
               SplitableIterable>,
               InvariantCheckable
{
    public static final int ROOT_SHIFT = 30;

    public abstract boolean isEmpty();

    public abstract T getValueOr(int shift,
                                 int index,
                                 T defaultValue);

    public abstract Holder find(int shift,
                                   int index);

    public abstract TrieNode assign(int shift,
                                       int index,
                                       T value,
                                       MutableDelta sizeDelta);

    public abstract TrieNode delete(int shift,
                                       int index,
                                       MutableDelta sizeDelta);

    public abstract int getShift();

    public abstract boolean isLeaf();

    public TrieNode trimmedToMinimumDepth()
    {
        return this;
    }

    public TrieNode paddedToMinimumDepthForShift(int shift)
    {
        TrieNode node = this;
        int nodeShift = node.getShift();
        while (nodeShift < shift) {
            nodeShift += 5;
            node = SingleBranchTrieNode.forBranchIndex(nodeShift, 0, node);
        }
        return node;
    }

    public static  TrieNode of()
    {
        return EmptyTrieNode.instance();
    }

    public static  TrieNode fromSource(int index,
                                             Indexed source,
                                             int offset,
                                             int limit)
    {
        final int size = Math.min(32, limit - offset);
        if (size < 0) {
            throw new IllegalArgumentException();
        }

        switch (size) {
            case 0:
                return of();

            case 1:
                return LeafTrieNode.of(index, source.get(offset));

            case 32:
                return FullBranchTrieNode.fromSource(index, source, offset);

            default:
                return MultiBranchTrieNode.forSource(index, size, source, offset);
        }
    }

    public static int shiftForIndex(int index)
    {
        switch (Integer.numberOfLeadingZeros(index)) {
            case 0:
            case 1:
                return 30;

            case 2:
            case 3:
            case 4:
            case 5:
            case 6:
                return 25;

            case 7:
            case 8:
            case 9:
            case 10:
            case 11:
                return 20;

            case 12:
            case 13:
            case 14:
            case 15:
            case 16:
                return 15;

            case 17:
            case 18:
            case 19:
            case 20:
            case 21:
                return 10;

            case 22:
            case 23:
            case 24:
            case 25:
            case 26:
                return 5;

            case 27:
            case 28:
            case 29:
            case 30:
            case 31:
            case 32:
                return 0;
        }
        throw new IllegalArgumentException();
    }
}