com.signalfx.shaded.jetty.util.ArrayTrie Maven / Gradle / Ivy
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// Copyright (c) 1995-2022 Mort Bay Consulting Pty Ltd and others.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
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// You may elect to redistribute this code under either of these licenses.
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package com.signalfx.shaded.jetty.util;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
/**
* A Trie String lookup data structure using a fixed size array.
* This implementation is always case insensitive and is optimal for
* a small number of fixed strings with few special characters. The
* Trie is stored in an array of lookup tables, each indexed by the
* next character of the key. Frequently used characters are directly
* indexed in each lookup table, whilst infrequently used characters
* must use a big character table.
*
* This Trie is very space efficient if the key characters are
* from ' ', '+', '-', ':', ';', '.', 'A' to 'Z' or 'a' to 'z'.
* Other ISO-8859-1 characters can be used by the key, but less space
* efficiently.
*
* This Trie is not Threadsafe and contains no mutual exclusion
* or deliberate memory barriers. It is intended for an ArrayTrie to be
* built by a single thread and then used concurrently by multiple threads
* and not mutated during that access. If concurrent mutations of the
* Trie is required external locks need to be applied.
*
*
* @param the entry type
*/
public class ArrayTrie extends AbstractTrie
{
/**
* The Size of a Trie row is how many characters can be looked
* up directly without going to a big index. This is set at
* 32 to cover case insensitive alphabet and a few other common
* characters.
*/
private static final int ROW_SIZE = 32;
/**
* The maximum capacity of the implementation. Over that,
* the 16 bit indexes can overflow and the trie
* cannot find existing entries anymore.
*/
private static final int MAX_CAPACITY = Character.MAX_VALUE - 1;
/**
* The index lookup table, this maps a character as a byte
* (ISO-8859-1 or UTF8) to an index within a Trie row
*/
private static final int[] __lookup =
{
// 0 1 2 3 4 5 6 7 8 9 A B C D E F
/*0*/-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
/*1*/-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
/*2*/31, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 26, -1, 27, 30, -1,
/*3*/-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 28, 29, -1, -1, -1, -1,
/*4*/-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
/*5*/15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
/*6*/-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
/*7*/15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1
};
/**
* The Trie rows in a single array which allows a lookup of row,character
* to the next row in the Trie. This is actually a 2 dimensional
* array that has been flattened to achieve locality of reference.
* The first ROW_SIZE entries are for row 0, then next ROW_SIZE
* entries are for row 1 etc. So in general instead of using
* _rows[row][index], we use _rows[row*ROW_SIZE+index] to look up
* the next row for a given character.
*
* The array is of characters rather than integers to save space.
*/
private final char[] _rowIndex;
/**
* The key (if any) for a Trie row.
* A row may be a leaf, a node or both in the Trie tree.
*/
private final String[] _key;
/**
* The value (if any) for a Trie row.
* A row may be a leaf, a node or both in the Trie tree.
*/
private final V[] _value;
/**
* A big index for each row.
* If a character outside of the lookup map is needed,
* then a big index will be created for the row, with
* 256 entries, one for each possible byte.
*/
private char[][] _bigIndex;
/**
* The number of rows allocated
*/
private char _rows;
public ArrayTrie()
{
this(128);
}
/**
* @param capacity The capacity of the trie, which at the worst case
* is the total number of characters of all keys stored in the Trie.
* The capacity needed is dependent of the shared prefixes of the keys.
* For example, a capacity of 6 nodes is required to store keys "foo"
* and "bar", but a capacity of only 4 is required to
* store "bar" and "bat".
*/
@SuppressWarnings("unchecked")
public ArrayTrie(int capacity)
{
super(true);
if (capacity > MAX_CAPACITY)
throw new IllegalArgumentException("Capacity " + capacity + " > " + MAX_CAPACITY);
_value = (V[])new Object[capacity + 1];
_rowIndex = new char[(capacity + 1) * ROW_SIZE];
_key = new String[capacity + 1];
}
@Override
public void clear()
{
_rows = 0;
Arrays.fill(_value, null);
Arrays.fill(_rowIndex, (char)0);
Arrays.fill(_key, null);
}
@Override
public boolean put(String s, V v)
{
int t = 0;
int k;
int limit = s.length();
if (limit > MAX_CAPACITY)
return false;
for (k = 0; k < limit; k++)
{
char c = s.charAt(k);
int index = __lookup[c & 0x7f];
if (index >= 0)
{
int idx = t * ROW_SIZE + index;
t = _rowIndex[idx];
if (t == 0)
{
_rows = (char)MathUtils.cappedAdd(_rows, 1, _value.length);
if (_rows == _value.length)
return false;
t = _rowIndex[idx] = _rows;
}
}
else if (c > 127)
throw new IllegalArgumentException("non ascii character");
else
{
if (_bigIndex == null)
_bigIndex = new char[_value.length][];
if (t >= _bigIndex.length)
return false;
char[] big = _bigIndex[t];
if (big == null)
big = _bigIndex[t] = new char[128];
t = big[c];
if (t == 0)
{
_rows = (char)MathUtils.cappedAdd(_rows, 1, _value.length);
if (_rows == _value.length)
return false;
t = big[c] = _rows;
}
}
}
if (t >= _key.length)
{
_rows = (char)_key.length;
return false;
}
_key[t] = v == null ? null : s;
_value[t] = v;
return true;
}
@Override
public V get(String s, int offset, int len)
{
int t = 0;
for (int i = 0; i < len; i++)
{
char c = s.charAt(offset + i);
if (c > 0x7f)
return null;
int index = __lookup[c & 0x7f];
if (index >= 0)
{
int idx = t * ROW_SIZE + index;
t = _rowIndex[idx];
if (t == 0)
return null;
}
else
{
char[] big = _bigIndex == null ? null : _bigIndex[t];
if (big == null)
return null;
t = big[c & 0x7f];
if (t == 0)
return null;
}
}
return _value[t];
}
@Override
public V get(ByteBuffer b, int offset, int len)
{
int t = 0;
for (int i = 0; i < len; i++)
{
byte c = b.get(offset + i);
int index = __lookup[c & 0x7f];
if (index >= 0)
{
int idx = t * ROW_SIZE + index;
t = _rowIndex[idx];
if (t == 0)
return null;
}
else
{
char[] big = _bigIndex == null ? null : _bigIndex[t];
if (big == null)
return null;
t = big[c];
if (t == 0)
return null;
}
}
return _value[t];
}
@Override
public V getBest(byte[] b, int offset, int len)
{
return getBest(0, b, offset, len);
}
@Override
public V getBest(ByteBuffer b, int offset, int len)
{
if (b.hasArray())
return getBest(0, b.array(), b.arrayOffset() + b.position() + offset, len);
return getBest(0, b, offset, len);
}
@Override
public V getBest(String s, int offset, int len)
{
return getBest(0, s, offset, len);
}
private V getBest(int t, String s, int offset, int len)
{
int pos = offset;
for (int i = 0; i < len; i++)
{
char c = s.charAt(pos++);
int index = __lookup[c & 0x7f];
int nt;
if (index >= 0)
{
int idx = t * ROW_SIZE + index;
nt = _rowIndex[idx];
if (nt == 0)
break;
}
else
{
char[] big = _bigIndex == null ? null : _bigIndex[t];
if (big == null)
break;
nt = big[c];
if (nt == 0)
break;
}
// Is this node a match ?
if (_key[t] != null)
{
// Recurse so we can remember this possibility
V best = getBest(nt, s, offset + i + 1, len - i - 1);
if (best != null)
return best;
return _value[t];
}
t = nt;
}
return _value[t];
}
private V getBest(int t, byte[] b, int offset, int len)
{
for (int i = 0; i < len; i++)
{
byte c = b[offset + i];
int index = __lookup[c & 0x7f];
int nt;
if (index >= 0)
{
int idx = t * ROW_SIZE + index;
nt = _rowIndex[idx];
if (nt == 0)
break;
}
else
{
char[] big = _bigIndex == null ? null : _bigIndex[t];
if (big == null)
break;
nt = big[c];
if (nt == 0)
break;
}
// Is this node is a match
if (_key[t] != null)
{
// Recurse so we can remember this possibility
V best = getBest(nt, b, offset + i + 1, len - i - 1);
if (best != null)
return best;
break;
}
t = nt;
}
return _value[t];
}
private V getBest(int t, ByteBuffer b, int offset, int len)
{
int pos = b.position() + offset;
for (int i = 0; i < len; i++)
{
if (pos >= b.limit())
return null;
byte c = b.get(pos++);
int index = __lookup[c & 0x7f];
int nt;
if (index >= 0)
{
int idx = t * ROW_SIZE + index;
nt = _rowIndex[idx];
if (nt == 0)
break;
}
else
{
char[] big = _bigIndex == null ? null : _bigIndex[t];
if (big == null)
break;
nt = big[c];
if (nt == 0)
break;
t = nt;
}
// Is this node a match
if (_key[t] != null)
{
// Recurse so we can remember this possibility
V best = getBest(nt, b, offset + i + 1, len - i - 1);
if (best != null)
return best;
break;
}
t = nt;
}
return _value[t];
}
@Override
public String toString()
{
int rows = _rows;
if (rows == 0)
return "{}";
StringBuilder buf = new StringBuilder();
char c = '{';
for (int i = 0; i <= rows; i++)
{
String key = _key[i];
if (key != null)
{
buf.append(c).append(key).append('=').append(_value[i]);
c = ',';
}
}
buf.append('}');
return buf.toString();
}
@Override
public Set keySet()
{
Set keys = new HashSet<>();
for (String k : _key)
if (k != null)
keys.add(k);
return keys;
}
@Override
public boolean isFull()
{
return _rows >= _key.length;
}
}