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	/*
	* Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package java.util.stream;

	import java.util.EnumMap;
	import java.util.Map;
	import java.util.Spliterator;

	/**
	* Flags corresponding to characteristics of streams and operations. Flags are
	* utilized by the stream framework to control, specialize or optimize
	* computation.
	*
	* <p>
	* Stream flags may be used to describe characteristics of several different
	* entities associated with streams: stream sources, intermediate operations,
	* and terminal operations. Not all stream flags are meaningful for all
	* entities; the following table summarizes which flags are meaningful in what
	* contexts:
	*
	* <div>
	* <table class="borderless">
	* <caption>Type Characteristics</caption>
	* <thead class="tableSubHeadingColor">
	* <tr>
	* <th colspan="2"> </th>
	* <th>{@code DISTINCT}</th>
	* <th>{@code SORTED}</th>
	* <th>{@code ORDERED}</th>
	* <th>{@code SIZED}</th>
	* <th>{@code SHORT_CIRCUIT}</th>
	* </tr>
	* </thead>
	* <tbody>
	* <tr>
	* <th colspan="2" class="tableSubHeadingColor">Stream source</th>
	* <td>Y</td>
	* <td>Y</td>
	* <td>Y</td>
	* <td>Y</td>
	* <td>N</td>
	* </tr>
	* <tr>
	* <th colspan="2" class="tableSubHeadingColor">Intermediate operation</th>
	* <td>PCI</td>
	* <td>PCI</td>
	* <td>PCI</td>
	* <td>PC</td>
	* <td>PI</td>
	* </tr>
	* <tr>
	* <th colspan="2" class="tableSubHeadingColor">Terminal operation</th>
	* <td>N</td>
	* <td>N</td>
	* <td>PC</td>
	* <td>N</td>
	* <td>PI</td>
	* </tr>
	* </tbody>
	* <tfoot>
	* <tr>
	* <th class="tableSubHeadingColor" colspan="2">Legend</th>
	* <th colspan="6" rowspan="7"> </th>
	* </tr>
	* <tr>
	* <th class="tableSubHeadingColor">Flag</th>
	* <th class="tableSubHeadingColor">Meaning</th>
	* <th colspan="6"></th>
	* </tr>
	* <tr><td>Y</td><td>Allowed</td></tr>
	* <tr><td>N</td><td>Invalid</td></tr>
	* <tr><td>P</td><td>Preserves</td></tr>
	* <tr><td>C</td><td>Clears</td></tr>
	* <tr><td>I</td><td>Injects</td></tr>
	* </tfoot>
	* </table>
	* </div>
	*
	* <p>In the above table, "PCI" means "may preserve, clear, or inject"; "PC"
	* means "may preserve or clear", "PI" means "may preserve or inject", and "N"
	* means "not valid".
	*
	* <p>Stream flags are represented by unioned bit sets, so that a single word
	* may describe all the characteristics of a given stream entity, and that, for
	* example, the flags for a stream source can be efficiently combined with the
	* flags for later operations on that stream.
	*
	* <p>The bit masks {@link #STREAM_MASK}, {@link #OP_MASK}, and
	* {@link #TERMINAL_OP_MASK} can be ANDed with a bit set of stream flags to
	* produce a mask containing only the valid flags for that entity type.
	*
	* <p>When describing a stream source, one only need describe what
	* characteristics that stream has; when describing a stream operation, one need
	* describe whether the operation preserves, injects, or clears that
	* characteristic. Accordingly, two bits are used for each flag, so as to allow
	* representing not only the presence of a characteristic, but how an
	* operation modifies that characteristic. There are two common forms in which
	* flag bits are combined into an {@code int} bit set. <em>Stream flags</em>
	* are a unioned bit set constructed by ORing the enum characteristic values of
	* {@link #set()} (or, more commonly, ORing the corresponding static named
	* constants prefixed with {@code IS_}). <em>Operation flags</em> are a unioned
	* bit set constructed by ORing the enum characteristic values of {@link #set()}
	* or {@link #clear()} (to inject, or clear, respectively, the corresponding
	* flag), or more commonly ORing the corresponding named constants prefixed with
	* {@code IS_} or {@code NOT_}. Flags that are not marked with {@code IS_} or
	* {@code NOT_} are implicitly treated as preserved. Care must be taken when
	* combining bitsets that the correct combining operations are applied in the
	* correct order.
	*
	* <p>
	* With the exception of {@link #SHORT_CIRCUIT}, stream characteristics can be
	* derived from the equivalent {@link java.util.Spliterator} characteristics:
	* {@link java.util.Spliterator#DISTINCT}, {@link java.util.Spliterator#SORTED},
	* {@link java.util.Spliterator#ORDERED}, and
	* {@link java.util.Spliterator#SIZED}. A spliterator characteristics bit set
	* can be converted to stream flags using the method
	* {@link #fromCharacteristics(java.util.Spliterator)} and converted back using
	* {@link #toCharacteristics(int)}. (The bit set
	* {@link #SPLITERATOR_CHARACTERISTICS_MASK} is used to AND with a bit set to
	* produce a valid spliterator characteristics bit set that can be converted to
	* stream flags.)
	*
	* <p>
	* The source of a stream encapsulates a spliterator. The characteristics of
	* that source spliterator when transformed to stream flags will be a proper
	* subset of stream flags of that stream.
	* For example:
	* <pre> {@code
	* Spliterator s = ...;
	* Stream stream = Streams.stream(s);
	* flagsFromSplitr = fromCharacteristics(s.characteristics());
	* assert(flagsFromSplitr & stream.getStreamFlags() == flagsFromSplitr);
	* }</pre>
	*
	* <p>
	* An intermediate operation, performed on an input stream to create a new
	* output stream, may preserve, clear or inject stream or operation
	* characteristics. Similarly, a terminal operation, performed on an input
	* stream to produce an output result may preserve, clear or inject stream or
	* operation characteristics. Preservation means that if that characteristic
	* is present on the input, then it is also present on the output. Clearing
	* means that the characteristic is not present on the output regardless of the
	* input. Injection means that the characteristic is present on the output
	* regardless of the input. If a characteristic is not cleared or injected then
	* it is implicitly preserved.
	*
	* <p>
	* A pipeline consists of a stream source encapsulating a spliterator, one or
	* more intermediate operations, and finally a terminal operation that produces
	* a result. At each stage of the pipeline, a combined stream and operation
	* flags can be calculated, using {@link #combineOpFlags(int, int)}. Such flags
	* ensure that preservation, clearing and injecting information is retained at
	* each stage.
	*
	* The combined stream and operation flags for the source stage of the pipeline
	* is calculated as follows:
	* <pre> {@code
	* int flagsForSourceStage = combineOpFlags(sourceFlags, INITIAL_OPS_VALUE);
	* }</pre>
	*
	* The combined stream and operation flags of each subsequent intermediate
	* operation stage in the pipeline is calculated as follows:
	* <pre> {@code
	* int flagsForThisStage = combineOpFlags(flagsForPreviousStage, thisOpFlags);
	* }</pre>
	*
	* Finally the flags output from the last intermediate operation of the pipeline
	* are combined with the operation flags of the terminal operation to produce
	* the flags output from the pipeline.
	*
	* <p>Those flags can then be used to apply optimizations. For example, if
	* {@code SIZED.isKnown(flags)} returns true then the stream size remains
	* constant throughout the pipeline, this information can be utilized to
	* pre-allocate data structures and combined with
	* {@link java.util.Spliterator#SUBSIZED} that information can be utilized to
	* perform concurrent in-place updates into a shared array.
	*
	* For specific details see the {@link AbstractPipeline} constructors.
	*
	* @since 1.8
	*/
	enum StreamOpFlag {

	/*
	* Each characteristic takes up 2 bits in a bit set to accommodate
	* preserving, clearing and setting/injecting information.
	*
	* This applies to stream flags, intermediate/terminal operation flags, and
	* combined stream and operation flags. Even though the former only requires
	* 1 bit of information per characteristic, is it more efficient when
	* combining flags to align set and inject bits.
	*
	* Characteristics belong to certain types, see the Type enum. Bit masks for
	* the types are constructed as per the following table:
	*
	* DISTINCT SORTED ORDERED SIZED SHORT_CIRCUIT
	* SPLITERATOR 01 01 01 01 00
	* STREAM 01 01 01 01 00
	* OP 11 11 11 10 01
	* TERMINAL_OP 00 00 10 00 01
	* UPSTREAM_TERMINAL_OP 00 00 10 00 00
	*
	* 01 = set/inject
	* 10 = clear
	* 11 = preserve
	*
	* Construction of the columns is performed using a simple builder for
	* non-zero values.
	*/


	// The following flags correspond to characteristics on Spliterator
	// and the values MUST be equal.
	//

	/**
	* Characteristic value signifying that, for each pair of
	* encountered elements in a stream {@code x, y}, {@code !x.equals(y)}.
	* <p>
	* A stream may have this value or an intermediate operation can preserve,
	* clear or inject this value.
	*/
	// 0, 0x00000001
	// Matches Spliterator.DISTINCT
	DISTINCT(0,
	set(Type.SPLITERATOR).set(Type.STREAM).setAndClear(Type.OP)),

	/**
	* Characteristic value signifying that encounter order follows a natural
	* sort order of comparable elements.
	* <p>
	* A stream can have this value or an intermediate operation can preserve,
	* clear or inject this value.
	* <p>
	* Note: The {@link java.util.Spliterator#SORTED} characteristic can define
	* a sort order with an associated non-null comparator. Augmenting flag
	* state with addition properties such that those properties can be passed
	* to operations requires some disruptive changes for a singular use-case.
	* Furthermore, comparing comparators for equality beyond that of identity
	* is likely to be unreliable. Therefore the {@code SORTED} characteristic
	* for a defined non-natural sort order is not mapped internally to the
	* {@code SORTED} flag.
	*/
	// 1, 0x00000004
	// Matches Spliterator.SORTED
	SORTED(1,
	set(Type.SPLITERATOR).set(Type.STREAM).setAndClear(Type.OP)),

	/**
	* Characteristic value signifying that an encounter order is
	* defined for stream elements.
	* <p>
	* A stream can have this value, an intermediate operation can preserve,
	* clear or inject this value, or a terminal operation can preserve or clear
	* this value.
	*/
	// 2, 0x00000010
	// Matches Spliterator.ORDERED
	ORDERED(2,
	set(Type.SPLITERATOR).set(Type.STREAM).setAndClear(Type.OP).clear(Type.TERMINAL_OP)
	.clear(Type.UPSTREAM_TERMINAL_OP)),

	/**
	* Characteristic value signifying that size of the stream
	* is of a known finite size that is equal to the known finite
	* size of the source spliterator input to the first stream
	* in the pipeline.
	* <p>
	* A stream can have this value or an intermediate operation can preserve or
	* clear this value.
	*/
	// 3, 0x00000040
	// Matches Spliterator.SIZED
	SIZED(3,
	set(Type.SPLITERATOR).set(Type.STREAM).clear(Type.OP)),

	// The following Spliterator characteristics are not currently used but a
	// gap in the bit set is deliberately retained to enable corresponding
	// stream flags if//when required without modification to other flag values.
	//
	// 4, 0x00000100 NONNULL(4, ...
	// 5, 0x00000400 IMMUTABLE(5, ...
	// 6, 0x00001000 CONCURRENT(6, ...
	// 7, 0x00004000 SUBSIZED(7, ...

	// The following 4 flags are currently undefined and a free for any further
	// spliterator characteristics.
	//
	// 8, 0x00010000
	// 9, 0x00040000
	// 10, 0x00100000
	// 11, 0x00400000

	// The following flags are specific to streams and operations
	//

	/**
	* Characteristic value signifying that an operation may short-circuit the
	* stream.
	* <p>
	* An intermediate operation can preserve or inject this value,
	* or a terminal operation can preserve or inject this value.
	*/
	// 12, 0x01000000
	SHORT_CIRCUIT(12,
	set(Type.OP).set(Type.TERMINAL_OP));

	// The following 2 flags are currently undefined and a free for any further
	// stream flags if/when required
	//
	// 13, 0x04000000
	// 14, 0x10000000
	// 15, 0x40000000

	/**
	* Type of a flag
	*/
	enum Type {
	/**
	* The flag is associated with spliterator characteristics.
	*/
	SPLITERATOR,

	/**
	* The flag is associated with stream flags.
	*/
	STREAM,

	/**
	* The flag is associated with intermediate operation flags.
	*/
	OP,

	/**
	* The flag is associated with terminal operation flags.
	*/
	TERMINAL_OP,

	/**
	* The flag is associated with terminal operation flags that are
	* propagated upstream across the last stateful operation boundary
	*/
	UPSTREAM_TERMINAL_OP
	}

	/**
	* The bit pattern for setting/injecting a flag.
	*/
	private static final int SET_BITS = 0b01;

	/**
	* The bit pattern for clearing a flag.
	*/
	private static final int CLEAR_BITS = 0b10;

	/**
	* The bit pattern for preserving a flag.
	*/
	private static final int PRESERVE_BITS = 0b11;

	private static MaskBuilder set(Type t) {
	return new MaskBuilder(new EnumMap<>(Type.class)).set(t);
	}

	private static class MaskBuilder {
	final Map<Type, Integer> map;

	MaskBuilder(Map<Type, Integer> map) {
	this.map = map;
	}

	MaskBuilder mask(Type t, Integer i) {
	map.put(t, i);
	return this;
	}

	MaskBuilder set(Type t) {
	return mask(t, SET_BITS);
	}

	MaskBuilder clear(Type t) {
	return mask(t, CLEAR_BITS);
	}

	MaskBuilder setAndClear(Type t) {
	return mask(t, PRESERVE_BITS);
	}

	Map<Type, Integer> build() {
	for (Type t : Type.values()) {
	map.putIfAbsent(t, 0b00);
	}
	return map;
	}
	}

	/**
	* The mask table for a flag, this is used to determine if a flag
	* corresponds to a certain flag type and for creating mask constants.
	*/
	private final Map<Type, Integer> maskTable;

	/**
	* The bit position in the bit mask.
	*/
	private final int bitPosition;

	/**
	* The set 2 bit set offset at the bit position.
	*/
	private final int set;

	/**
	* The clear 2 bit set offset at the bit position.
	*/
	private final int clear;

	/**
	* The preserve 2 bit set offset at the bit position.
	*/
	private final int preserve;

	private StreamOpFlag(int position, MaskBuilder maskBuilder) {
	this.maskTable = maskBuilder.build();
	// Two bits per flag
	position *= 2;
	this.bitPosition = position;
	this.set = SET_BITS << position;
	this.clear = CLEAR_BITS << position;
	this.preserve = PRESERVE_BITS << position;
	}

	/**
	* Gets the bitmap associated with setting this characteristic.
	*
	* @return the bitmap for setting this characteristic
	*/
	int set() {
	return set;
	}

	/**
	* Gets the bitmap associated with clearing this characteristic.
	*
	* @return the bitmap for clearing this characteristic
	*/
	int clear() {
	return clear;
	}

	/**
	* Determines if this flag is a stream-based flag.
	*
	* @return true if a stream-based flag, otherwise false.
	*/
	boolean isStreamFlag() {
	return maskTable.get(Type.STREAM) > 0;
	}

	/**
	* Checks if this flag is set on stream flags, injected on operation flags,
	* and injected on combined stream and operation flags.
	*
	* @param flags the stream flags, operation flags, or combined stream and
	* operation flags
	* @return true if this flag is known, otherwise false.
	*/
	boolean isKnown(int flags) {
	return (flags & preserve) == set;
	}

	/**
	* Checks if this flag is cleared on operation flags or combined stream and
	* operation flags.
	*
	* @param flags the operation flags or combined stream and operations flags.
	* @return true if this flag is preserved, otherwise false.
	*/
	boolean isCleared(int flags) {
	return (flags & preserve) == clear;
	}

	/**
	* Checks if this flag is preserved on combined stream and operation flags.
	*
	* @param flags the combined stream and operations flags.
	* @return true if this flag is preserved, otherwise false.
	*/
	boolean isPreserved(int flags) {
	return (flags & preserve) == preserve;
	}

	/**
	* Determines if this flag can be set for a flag type.
	*
	* @param t the flag type.
	* @return true if this flag can be set for the flag type, otherwise false.
	*/
	boolean canSet(Type t) {
	return (maskTable.get(t) & SET_BITS) > 0;
	}

	/**
	* The bit mask for spliterator characteristics
	*/
	static final int SPLITERATOR_CHARACTERISTICS_MASK = createMask(Type.SPLITERATOR);

	/**
	* The bit mask for source stream flags.
	*/
	static final int STREAM_MASK = createMask(Type.STREAM);

	/**
	* The bit mask for intermediate operation flags.
	*/
	static final int OP_MASK = createMask(Type.OP);

	/**
	* The bit mask for terminal operation flags.
	*/
	static final int TERMINAL_OP_MASK = createMask(Type.TERMINAL_OP);

	/**
	* The bit mask for upstream terminal operation flags.
	*/
	static final int UPSTREAM_TERMINAL_OP_MASK = createMask(Type.UPSTREAM_TERMINAL_OP);

	private static int createMask(Type t) {
	int mask = 0;
	for (StreamOpFlag flag : StreamOpFlag.values()) {
	mask \|= flag.maskTable.get(t) << flag.bitPosition;
	}
	return mask;
	}

	/**
	* Complete flag mask.
	*/
	private static final int FLAG_MASK = createFlagMask();

	private static int createFlagMask() {
	int mask = 0;
	for (StreamOpFlag flag : StreamOpFlag.values()) {
	mask \|= flag.preserve;
	}
	return mask;
	}

	/**
	* Flag mask for stream flags that are set.
	*/
	private static final int FLAG_MASK_IS = STREAM_MASK;

	/**
	* Flag mask for stream flags that are cleared.
	*/
	private static final int FLAG_MASK_NOT = STREAM_MASK << 1;

	/**
	* The initial value to be combined with the stream flags of the first
	* stream in the pipeline.
	*/
	static final int INITIAL_OPS_VALUE = FLAG_MASK_IS \| FLAG_MASK_NOT;

	/**
	* The bit value to set or inject {@link #DISTINCT}.
	*/
	static final int IS_DISTINCT = DISTINCT.set;

	/**
	* The bit value to clear {@link #DISTINCT}.
	*/
	static final int NOT_DISTINCT = DISTINCT.clear;

	/**
	* The bit value to set or inject {@link #SORTED}.
	*/
	static final int IS_SORTED = SORTED.set;

	/**
	* The bit value to clear {@link #SORTED}.
	*/
	static final int NOT_SORTED = SORTED.clear;

	/**
	* The bit value to set or inject {@link #ORDERED}.
	*/
	static final int IS_ORDERED = ORDERED.set;

	/**
	* The bit value to clear {@link #ORDERED}.
	*/
	static final int NOT_ORDERED = ORDERED.clear;

	/**
	* The bit value to set {@link #SIZED}.
	*/
	static final int IS_SIZED = SIZED.set;

	/**
	* The bit value to clear {@link #SIZED}.
	*/
	static final int NOT_SIZED = SIZED.clear;

	/**
	* The bit value to inject {@link #SHORT_CIRCUIT}.
	*/
	static final int IS_SHORT_CIRCUIT = SHORT_CIRCUIT.set;

	private static int getMask(int flags) {
	return (flags == 0)
	? FLAG_MASK
	: ~(flags \| ((FLAG_MASK_IS & flags) << 1) \| ((FLAG_MASK_NOT & flags) >> 1));
	}

	/**
	* Combines stream or operation flags with previously combined stream and
	* operation flags to produce updated combined stream and operation flags.
	* <p>
	* A flag set on stream flags or injected on operation flags,
	* and injected combined stream and operation flags,
	* will be injected on the updated combined stream and operation flags.
	*
	* <p>
	* A flag set on stream flags or injected on operation flags,
	* and cleared on the combined stream and operation flags,
	* will be cleared on the updated combined stream and operation flags.
	*
	* <p>
	* A flag set on the stream flags or injected on operation flags,
	* and preserved on the combined stream and operation flags,
	* will be injected on the updated combined stream and operation flags.
	*
	* <p>
	* A flag not set on the stream flags or cleared/preserved on operation
	* flags, and injected on the combined stream and operation flags,
	* will be injected on the updated combined stream and operation flags.
	*
	* <p>
	* A flag not set on the stream flags or cleared/preserved on operation
	* flags, and cleared on the combined stream and operation flags,
	* will be cleared on the updated combined stream and operation flags.
	*
	* <p>
	* A flag not set on the stream flags,
	* and preserved on the combined stream and operation flags
	* will be preserved on the updated combined stream and operation flags.
	*
	* <p>
	* A flag cleared on operation flags,
	* and preserved on the combined stream and operation flags
	* will be cleared on the updated combined stream and operation flags.
	*
	* <p>
	* A flag preserved on operation flags,
	* and preserved on the combined stream and operation flags
	* will be preserved on the updated combined stream and operation flags.
	*
	* @param newStreamOrOpFlags the stream or operation flags.
	* @param prevCombOpFlags previously combined stream and operation flags.
	* The value {#link INITIAL_OPS_VALUE} must be used as the seed value.
	* @return the updated combined stream and operation flags.
	*/
	static int combineOpFlags(int newStreamOrOpFlags, int prevCombOpFlags) {
	// 0x01 or 0x10 nibbles are transformed to 0x11
	// 0x00 nibbles remain unchanged
	// Then all the bits are flipped
	// Then the result is logically or'ed with the operation flags.
	return (prevCombOpFlags & StreamOpFlag.getMask(newStreamOrOpFlags)) \| newStreamOrOpFlags;
	}

	/**
	* Converts combined stream and operation flags to stream flags.
	*
	* <p>Each flag injected on the combined stream and operation flags will be
	* set on the stream flags.
	*
	* @param combOpFlags the combined stream and operation flags.
	* @return the stream flags.
	*/
	static int toStreamFlags(int combOpFlags) {
	// By flipping the nibbles 0x11 become 0x00 and 0x01 become 0x10
	// Shift left 1 to restore set flags and mask off anything other than the set flags
	return ((~combOpFlags) >> 1) & FLAG_MASK_IS & combOpFlags;
	}

	/**
	* Converts stream flags to a spliterator characteristic bit set.
	*
	* @param streamFlags the stream flags.
	* @return the spliterator characteristic bit set.
	*/
	static int toCharacteristics(int streamFlags) {
	return streamFlags & SPLITERATOR_CHARACTERISTICS_MASK;
	}

	/**
	* Converts a spliterator characteristic bit set to stream flags.
	*
	* @implSpec
	* If the spliterator is naturally {@code SORTED} (the associated
	* {@code Comparator} is {@code null}) then the characteristic is converted
	* to the {@link #SORTED} flag, otherwise the characteristic is not
	* converted.
	*
	* @param spliterator the spliterator from which to obtain characteristic
	* bit set.
	* @return the stream flags.
	*/
	static int fromCharacteristics(Spliterator<?> spliterator) {
	int characteristics = spliterator.characteristics();
	if ((characteristics & Spliterator.SORTED) != 0 && spliterator.getComparator() != null) {
	// Do not propagate the SORTED characteristic if it does not correspond
	// to a natural sort order
	return characteristics & SPLITERATOR_CHARACTERISTICS_MASK & ~Spliterator.SORTED;
	}
	else {
	return characteristics & SPLITERATOR_CHARACTERISTICS_MASK;
	}
	}

	/**
	* Converts a spliterator characteristic bit set to stream flags.
	*
	* @param characteristics the spliterator characteristic bit set.
	* @return the stream flags.
	*/
	static int fromCharacteristics(int characteristics) {
	return characteristics & SPLITERATOR_CHARACTERISTICS_MASK;
	}
	}

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