xref: /external/icu/icu4j/main/classes/collate/src/com/ibm/icu/impl/coll/Collation.java

/*
*******************************************************************************
* Copyright (C) 2010-2015, International Business Machines
* Corporation and others.  All Rights Reserved.
*******************************************************************************
* Collation.java, ported from collation.h/.cpp
*
* C++ version created on: 2010oct27
* created by: Markus W. Scherer
*/

package com.ibm.icu.impl.coll;

/**
 * Collation v2 basic definitions and static helper functions.
 *
 * Data structures except for expansion tables store 32-bit CEs which are
 * either specials (see tags below) or are compact forms of 64-bit CEs.
 */
public final class Collation {
    /** UChar32 U_SENTINEL.
     * TODO: Create a common, public constant?
     */
    public static final int SENTINEL_CP = -1;

    // ICU4C compare() API returns enum UCollationResult values (with UCOL_ prefix).
    // ICU4J just returns int. We use these constants for ease of porting.
    public static final int LESS = -1;
    public static final int EQUAL = 0;
    public static final int GREATER = 1;

    // Special sort key bytes for all levels.
    public static final int TERMINATOR_BYTE = 0;
    public static final int LEVEL_SEPARATOR_BYTE = 1;

    /** The secondary/tertiary lower limit for tailoring before any root elements. */
    static final int BEFORE_WEIGHT16 = 0x100;

    /**
     * Merge-sort-key separator.
     * Same as the unique primary and identical-level weights of U+FFFE.
     * Must not be used as primary compression low terminator.
     * Otherwise usable.
     */
    public static final int MERGE_SEPARATOR_BYTE = 2;
    public static final long MERGE_SEPARATOR_PRIMARY = 0x02000000;  // U+FFFE
    static final int MERGE_SEPARATOR_CE32 = 0x02000505;  // U+FFFE

    /**
     * Primary compression low terminator, must be greater than MERGE_SEPARATOR_BYTE.
     * Reserved value in primary second byte if the lead byte is compressible.
     * Otherwise usable in all CE weight bytes.
     */
    public static final int PRIMARY_COMPRESSION_LOW_BYTE = 3;
    /**
     * Primary compression high terminator.
     * Reserved value in primary second byte if the lead byte is compressible.
     * Otherwise usable in all CE weight bytes.
     */
    public static final int PRIMARY_COMPRESSION_HIGH_BYTE = 0xff;

    /** Default secondary/tertiary weight lead byte. */
    static final int COMMON_BYTE = 5;
    public static final int COMMON_WEIGHT16 = 0x0500;
    /** Middle 16 bits of a CE with a common secondary weight. */
    static final int COMMON_SECONDARY_CE = 0x05000000;
    /** Lower 16 bits of a CE with a common tertiary weight. */
    static final int COMMON_TERTIARY_CE = 0x0500;
    /** Lower 32 bits of a CE with common secondary and tertiary weights. */
    public static final int COMMON_SEC_AND_TER_CE = 0x05000500;

    static final int SECONDARY_MASK = 0xffff0000;
    public static final int CASE_MASK = 0xc000;
    static final int SECONDARY_AND_CASE_MASK = SECONDARY_MASK | CASE_MASK;
    /** Only the 2*6 bits for the pure tertiary weight. */
    public static final int ONLY_TERTIARY_MASK = 0x3f3f;
    /** Only the secondary & tertiary bits; no case, no quaternary. */
    static final int ONLY_SEC_TER_MASK = SECONDARY_MASK | ONLY_TERTIARY_MASK;
    /** Case bits and tertiary bits. */
    static final int CASE_AND_TERTIARY_MASK = CASE_MASK | ONLY_TERTIARY_MASK;
    public static final int QUATERNARY_MASK = 0xc0;
    /** Case bits and quaternary bits. */
    public static final int CASE_AND_QUATERNARY_MASK = CASE_MASK | QUATERNARY_MASK;

    static final int UNASSIGNED_IMPLICIT_BYTE = 0xfe;  // compressible
    /**
     * First unassigned: AlphabeticIndex overflow boundary.
     * We want a 3-byte primary so that it fits into the root elements table.
     *
     * This 3-byte primary will not collide with
     * any unassigned-implicit 4-byte primaries because
     * the first few hundred Unicode code points all have real mappings.
     */
    static final long FIRST_UNASSIGNED_PRIMARY = 0xfe040200L;

    static final int TRAIL_WEIGHT_BYTE = 0xff;  // not compressible
    static final long FIRST_TRAILING_PRIMARY = 0xff020200L;  // [first trailing]
    public static final long MAX_PRIMARY = 0xffff0000L;  // U+FFFF
    static final int MAX_REGULAR_CE32 = 0xffff0505;  // U+FFFF

    // CE32 value for U+FFFD as well as illegal UTF-8 byte sequences (which behave like U+FFFD).
    // We use the third-highest primary weight for U+FFFD (as in UCA 6.3+).
    public static final long FFFD_PRIMARY = MAX_PRIMARY - 0x20000;
    static final int FFFD_CE32 = MAX_REGULAR_CE32 - 0x20000;

    /**
     * A CE32 is special if its low byte is this or greater.
     * Impossible case bits 11 mark special CE32s.
     * This value itself is used to indicate a fallback to the base collator.
     */
    static final int SPECIAL_CE32_LOW_BYTE = 0xc0;
    static final int FALLBACK_CE32 = SPECIAL_CE32_LOW_BYTE;
    /**
     * Low byte of a long-primary special CE32.
     */
    static final int LONG_PRIMARY_CE32_LOW_BYTE = 0xc1;  // SPECIAL_CE32_LOW_BYTE | LONG_PRIMARY_TAG

    static final int UNASSIGNED_CE32 = 0xffffffff;  // Compute an unassigned-implicit CE.

    static final int NO_CE32 = 1;

    /** No CE: End of input. Only used in runtime code, not stored in data. */
    static final long NO_CE_PRIMARY = 1;  // not a left-adjusted weight
    static final int NO_CE_WEIGHT16 = 0x0100;  // weight of LEVEL_SEPARATOR_BYTE
    public static final long NO_CE = 0x101000100L;  // NO_CE_PRIMARY, NO_CE_WEIGHT16, NO_CE_WEIGHT16

    /** Sort key levels. */

    /** Unspecified level. */
    public static final int NO_LEVEL = 0;
    public static final int PRIMARY_LEVEL = 1;
    public static final int SECONDARY_LEVEL = 2;
    public static final int CASE_LEVEL = 3;
    public static final int TERTIARY_LEVEL = 4;
    public static final int QUATERNARY_LEVEL = 5;
    public static final int IDENTICAL_LEVEL = 6;
    /** Beyond sort key bytes. */
    public static final int ZERO_LEVEL = 7;

    /**
     * Sort key level flags: xx_FLAG = 1 << xx_LEVEL.
     * In Java, use enum Level with flag() getters, or use EnumSet rather than hand-made bit sets.
     */
    static final int NO_LEVEL_FLAG = 1;
    static final int PRIMARY_LEVEL_FLAG = 2;
    static final int SECONDARY_LEVEL_FLAG = 4;
    static final int CASE_LEVEL_FLAG = 8;
    static final int TERTIARY_LEVEL_FLAG = 0x10;
    static final int QUATERNARY_LEVEL_FLAG = 0x20;
    static final int IDENTICAL_LEVEL_FLAG = 0x40;
    static final int ZERO_LEVEL_FLAG = 0x80;

    /**
     * Special-CE32 tags, from bits 3..0 of a special 32-bit CE.
     * Bits 31..8 are available for tag-specific data.
     * Bits  5..4: Reserved. May be used in the future to indicate lccc!=0 and tccc!=0.
     */

    /**
     * Fall back to the base collator.
     * This is the tag value in SPECIAL_CE32_LOW_BYTE and FALLBACK_CE32.
     * Bits 31..8: Unused, 0.
     */
    static final int FALLBACK_TAG = 0;
    /**
     * Long-primary CE with COMMON_SEC_AND_TER_CE.
     * Bits 31..8: Three-byte primary.
     */
    static final int LONG_PRIMARY_TAG = 1;
    /**
     * Long-secondary CE with zero primary.
     * Bits 31..16: Secondary weight.
     * Bits 15.. 8: Tertiary weight.
     */
    static final int LONG_SECONDARY_TAG = 2;
    /**
     * Unused.
     * May be used in the future for single-byte secondary CEs (SHORT_SECONDARY_TAG),
     * storing the secondary in bits 31..24, the ccc in bits 23..16,
     * and the tertiary in bits 15..8.
     */
    static final int RESERVED_TAG_3 = 3;
    /**
     * Latin mini expansions of two simple CEs [pp, 05, tt] [00, ss, 05].
     * Bits 31..24: Single-byte primary weight pp of the first CE.
     * Bits 23..16: Tertiary weight tt of the first CE.
     * Bits 15.. 8: Secondary weight ss of the second CE.
     */
    static final int LATIN_EXPANSION_TAG = 4;
    /**
     * Points to one or more simple/long-primary/long-secondary 32-bit CE32s.
     * Bits 31..13: Index into int table.
     * Bits 12.. 8: Length=1..31.
     */
    static final int EXPANSION32_TAG = 5;
    /**
     * Points to one or more 64-bit CEs.
     * Bits 31..13: Index into CE table.
     * Bits 12.. 8: Length=1..31.
     */
    static final int EXPANSION_TAG = 6;
    /**
     * Builder data, used only in the CollationDataBuilder, not in runtime data.
     *
     * If bit 8 is 0: Builder context, points to a list of context-sensitive mappings.
     * Bits 31..13: Index to the builder's list of ConditionalCE32 for this character.
     * Bits 12.. 9: Unused, 0.
     *
     * If bit 8 is 1 (IS_BUILDER_JAMO_CE32): Builder-only jamoCE32 value.
     * The builder fetches the Jamo CE32 from the trie.
     * Bits 31..13: Jamo code point.
     * Bits 12.. 9: Unused, 0.
     */
    static final int BUILDER_DATA_TAG = 7;
    /**
     * Points to prefix trie.
     * Bits 31..13: Index into prefix/contraction data.
     * Bits 12.. 8: Unused, 0.
     */
    static final int PREFIX_TAG = 8;
    /**
     * Points to contraction data.
     * Bits 31..13: Index into prefix/contraction data.
     * Bits 12..11: Unused, 0.
     * Bit      10: CONTRACT_TRAILING_CCC flag.
     * Bit       9: CONTRACT_NEXT_CCC flag.
     * Bit       8: CONTRACT_SINGLE_CP_NO_MATCH flag.
     */
    static final int CONTRACTION_TAG = 9;
    /**
     * Decimal digit.
     * Bits 31..13: Index into int table for non-numeric-collation CE32.
     * Bit      12: Unused, 0.
     * Bits 11.. 8: Digit value 0..9.
     */
    static final int DIGIT_TAG = 10;
    /**
     * Tag for U+0000, for moving the NUL-termination handling
     * from the regular fastpath into specials-handling code.
     * Bits 31..8: Unused, 0.
     */
    static final int U0000_TAG = 11;
    /**
     * Tag for a Hangul syllable.
     * Bits 31..9: Unused, 0.
     * Bit      8: HANGUL_NO_SPECIAL_JAMO flag.
     */
    static final int HANGUL_TAG = 12;
    /**
     * Tag for a lead surrogate code unit.
     * Optional optimization for UTF-16 string processing.
     * Bits 31..10: Unused, 0.
     *       9.. 8: =0: All associated supplementary code points are unassigned-implict.
     *              =1: All associated supplementary code points fall back to the base data.
     *              else: (Normally 2) Look up the data for the supplementary code point.
     */
    static final int LEAD_SURROGATE_TAG = 13;
    /**
     * Tag for CEs with primary weights in code point order.
     * Bits 31..13: Index into CE table, for one data "CE".
     * Bits 12.. 8: Unused, 0.
     *
     * This data "CE" has the following bit fields:
     * Bits 63..32: Three-byte primary pppppp00.
     *      31.. 8: Start/base code point of the in-order range.
     *           7: Flag isCompressible primary.
     *       6.. 0: Per-code point primary-weight increment.
     */
    static final int OFFSET_TAG = 14;
    /**
     * Implicit CE tag. Compute an unassigned-implicit CE.
     * All bits are set (UNASSIGNED_CE32=0xffffffff).
     */
    static final int IMPLICIT_TAG = 15;

    static boolean isAssignedCE32(int ce32) {
        return ce32 != FALLBACK_CE32 && ce32 != UNASSIGNED_CE32;
    }

    /**
     * We limit the number of CEs in an expansion
     * so that we can use a small number of length bits in the data structure,
     * and so that an implementation can copy CEs at runtime without growing a destination buffer.
     */
    static final int MAX_EXPANSION_LENGTH = 31;
    static final int MAX_INDEX = 0x7ffff;

    /**
     * Set if there is no match for the single (no-suffix) character itself.
     * This is only possible if there is a prefix.
     * In this case, discontiguous contraction matching cannot add combining marks
     * starting from an empty suffix.
     * The default CE32 is used anyway if there is no suffix match.
     */
    static final int CONTRACT_SINGLE_CP_NO_MATCH = 0x100;
    /** Set if the first character of every contraction suffix has lccc!=0. */
    static final int CONTRACT_NEXT_CCC = 0x200;
    /** Set if any contraction suffix ends with lccc!=0. */
    static final int CONTRACT_TRAILING_CCC = 0x400;

    /** For HANGUL_TAG: None of its Jamo CE32s isSpecialCE32(). */
    static final int HANGUL_NO_SPECIAL_JAMO = 0x100;

    static final int LEAD_ALL_UNASSIGNED = 0;
    static final int LEAD_ALL_FALLBACK = 0x100;
    static final int LEAD_MIXED = 0x200;
    static final int LEAD_TYPE_MASK = 0x300;

    static int makeLongPrimaryCE32(long p) { return (int)(p | LONG_PRIMARY_CE32_LOW_BYTE); }

    /** Turns the long-primary CE32 into a primary weight pppppp00. */
    static long primaryFromLongPrimaryCE32(int ce32) {
        return (long)ce32 & 0xffffff00L;
    }
    static long ceFromLongPrimaryCE32(int ce32) {
        return ((long)(ce32 & 0xffffff00) << 32) | COMMON_SEC_AND_TER_CE;
    }

    static int makeLongSecondaryCE32(int lower32) {
        return lower32 | SPECIAL_CE32_LOW_BYTE | LONG_SECONDARY_TAG;
    }
    static long ceFromLongSecondaryCE32(int ce32) {
        return (long)ce32 & 0xffffff00L;
    }

    /** Makes a special CE32 with tag, index and length. */
    static int makeCE32FromTagIndexAndLength(int tag, int index, int length) {
        return (index << 13) | (length << 8) | SPECIAL_CE32_LOW_BYTE | tag;
    }
    /** Makes a special CE32 with only tag and index. */
    static int makeCE32FromTagAndIndex(int tag, int index) {
        return (index << 13) | SPECIAL_CE32_LOW_BYTE | tag;
    }

    static boolean isSpecialCE32(int ce32) {
        return (ce32 & 0xff) >= SPECIAL_CE32_LOW_BYTE;
    }

    static int tagFromCE32(int ce32) {
        return ce32 & 0xf;
    }

    static boolean hasCE32Tag(int ce32, int tag) {
        return isSpecialCE32(ce32) && tagFromCE32(ce32) == tag;
    }

    static boolean isLongPrimaryCE32(int ce32) {
        return hasCE32Tag(ce32, LONG_PRIMARY_TAG);
    }

    static boolean isSimpleOrLongCE32(int ce32) {
        return !isSpecialCE32(ce32) ||
                tagFromCE32(ce32) == LONG_PRIMARY_TAG ||
                tagFromCE32(ce32) == LONG_SECONDARY_TAG;
    }

    /**
     * @return true if the ce32 yields one or more CEs without further data lookups
     */
    static boolean isSelfContainedCE32(int ce32) {
        return !isSpecialCE32(ce32) ||
                tagFromCE32(ce32) == LONG_PRIMARY_TAG ||
                tagFromCE32(ce32) == LONG_SECONDARY_TAG ||
                tagFromCE32(ce32) == LATIN_EXPANSION_TAG;
    }

    static boolean isPrefixCE32(int ce32) {
        return hasCE32Tag(ce32, PREFIX_TAG);
    }

    static boolean isContractionCE32(int ce32) {
        return hasCE32Tag(ce32, CONTRACTION_TAG);
    }

    static boolean ce32HasContext(int ce32) {
        return isSpecialCE32(ce32) &&
                (tagFromCE32(ce32) == PREFIX_TAG ||
                tagFromCE32(ce32) == CONTRACTION_TAG);
    }

    /**
     * Get the first of the two Latin-expansion CEs encoded in ce32.
     * @see LATIN_EXPANSION_TAG
     */
    static long latinCE0FromCE32(int ce32) {
        return ((long)(ce32 & 0xff000000) << 32) | COMMON_SECONDARY_CE | ((ce32 & 0xff0000) >> 8);
    }

    /**
     * Get the second of the two Latin-expansion CEs encoded in ce32.
     * @see LATIN_EXPANSION_TAG
     */
    static long latinCE1FromCE32(int ce32) {
        return (((long)ce32 & 0xff00) << 16) | COMMON_TERTIARY_CE;
    }

    /**
     * Returns the data index from a special CE32.
     */
    static int indexFromCE32(int ce32) {
        return ce32 >>> 13;
    }

    /**
     * Returns the data length from a ce32.
     */
    static int lengthFromCE32(int ce32) {
        return (ce32 >> 8) & 31;
    }

    /**
     * Returns the digit value from a DIGIT_TAG ce32.
     */
    static char digitFromCE32(int ce32) {
        return (char)((ce32 >> 8) & 0xf);
    }

    /** Returns a 64-bit CE from a simple CE32 (not special). */
    static long ceFromSimpleCE32(int ce32) {
        // normal form ppppsstt -> pppp0000ss00tt00
        assert (ce32 & 0xff) < SPECIAL_CE32_LOW_BYTE;
        return ((long)(ce32 & 0xffff0000) << 32) | ((long)(ce32 & 0xff00) << 16) | ((ce32 & 0xff) << 8);
    }

    /** Returns a 64-bit CE from a simple/long-primary/long-secondary CE32. */
    static long ceFromCE32(int ce32) {
        int tertiary = ce32 & 0xff;
        if(tertiary < SPECIAL_CE32_LOW_BYTE) {
            // normal form ppppsstt -> pppp0000ss00tt00
            return ((long)(ce32 & 0xffff0000) << 32) | ((long)(ce32 & 0xff00) << 16) | (tertiary << 8);
        } else {
            ce32 -= tertiary;
            if((tertiary & 0xf) == LONG_PRIMARY_TAG) {
                // long-primary form ppppppC1 -> pppppp00050000500
                return ((long)ce32 << 32) | COMMON_SEC_AND_TER_CE;
            } else {
                // long-secondary form ssssttC2 -> 00000000sssstt00
                assert (tertiary & 0xf) == LONG_SECONDARY_TAG;
                return ce32 & 0xffffffffL;
            }
        }
    }

    /** Creates a CE from a primary weight. */
    public static long makeCE(long p) {
        return (p << 32) | COMMON_SEC_AND_TER_CE;
    }
    /**
     * Creates a CE from a primary weight,
     * 16-bit secondary/tertiary weights, and a 2-bit quaternary.
     */
    static long makeCE(long p, int s, int t, int q) {
        return (p << 32) | ((long)s << 16) | t | (q << 6);
    }

    /**
     * Increments a 2-byte primary by a code point offset.
     */
    public static long incTwoBytePrimaryByOffset(long basePrimary, boolean isCompressible,
                                              int offset) {
        // Extract the second byte, minus the minimum byte value,
        // plus the offset, modulo the number of usable byte values, plus the minimum.
        // Reserve the PRIMARY_COMPRESSION_LOW_BYTE and high byte if necessary.
        long primary;
        if(isCompressible) {
            offset += ((int)(basePrimary >> 16) & 0xff) - 4;
            primary = ((offset % 251) + 4) << 16;
            offset /= 251;
        } else {
            offset += ((int)(basePrimary >> 16) & 0xff) - 2;
            primary = ((offset % 254) + 2) << 16;
            offset /= 254;
        }
        // First byte, assume no further overflow.
        return primary | ((basePrimary & 0xff000000L) + ((long)offset << 24));
    }

    /**
     * Increments a 3-byte primary by a code point offset.
     */
    public static long incThreeBytePrimaryByOffset(long basePrimary, boolean isCompressible,
                                                int offset) {
        // Extract the third byte, minus the minimum byte value,
        // plus the offset, modulo the number of usable byte values, plus the minimum.
        offset += ((int)(basePrimary >> 8) & 0xff) - 2;
        long primary = ((offset % 254) + 2) << 8;
        offset /= 254;
        // Same with the second byte,
        // but reserve the PRIMARY_COMPRESSION_LOW_BYTE and high byte if necessary.
        if(isCompressible) {
            offset += ((int)(basePrimary >> 16) & 0xff) - 4;
            primary |= ((offset % 251) + 4) << 16;
            offset /= 251;
        } else {
            offset += ((int)(basePrimary >> 16) & 0xff) - 2;
            primary |= ((offset % 254) + 2) << 16;
            offset /= 254;
        }
        // First byte, assume no further overflow.
        return primary | ((basePrimary & 0xff000000L) + ((long)offset << 24));
    }

    /**
     * Decrements a 2-byte primary by one range step (1..0x7f).
     */
    static long decTwoBytePrimaryByOneStep(long basePrimary, boolean isCompressible, int step) {
        // Extract the second byte, minus the minimum byte value,
        // minus the step, modulo the number of usable byte values, plus the minimum.
        // Reserve the PRIMARY_COMPRESSION_LOW_BYTE and high byte if necessary.
        // Assume no further underflow for the first byte.
        assert(0 < step && step <= 0x7f);
        int byte2 = ((int)(basePrimary >> 16) & 0xff) - step;
        if(isCompressible) {
            if(byte2 < 4) {
                byte2 += 251;
                basePrimary -= 0x1000000;
            }
        } else {
            if(byte2 < 2) {
                byte2 += 254;
                basePrimary -= 0x1000000;
            }
        }
        return (basePrimary & 0xff000000L) | (byte2 << 16);
    }

    /**
     * Decrements a 3-byte primary by one range step (1..0x7f).
     */
    static long decThreeBytePrimaryByOneStep(long basePrimary, boolean isCompressible, int step) {
        // Extract the third byte, minus the minimum byte value,
        // minus the step, modulo the number of usable byte values, plus the minimum.
        assert(0 < step && step <= 0x7f);
        int byte3 = ((int)(basePrimary >> 8) & 0xff) - step;
        if(byte3 >= 2) {
            return (basePrimary & 0xffff0000L) | (byte3 << 8);
        }
        byte3 += 254;
        // Same with the second byte,
        // but reserve the PRIMARY_COMPRESSION_LOW_BYTE and high byte if necessary.
        int byte2 = ((int)(basePrimary >> 16) & 0xff) - 1;
        if(isCompressible) {
            if(byte2 < 4) {
                byte2 = 0xfe;
                basePrimary -= 0x1000000;
            }
        } else {
            if(byte2 < 2) {
                byte2 = 0xff;
                basePrimary -= 0x1000000;
            }
        }
        // First byte, assume no further underflow.
        return (basePrimary & 0xff000000L) | (byte2 << 16) | (byte3 << 8);
    }

    /**
     * Computes a 3-byte primary for c's OFFSET_TAG data "CE".
     */
    static long getThreeBytePrimaryForOffsetData(int c, long dataCE) {
        long p = dataCE >>> 32;  // three-byte primary pppppp00
        int lower32 = (int)dataCE;  // base code point b & step s: bbbbbbss (bit 7: isCompressible)
        int offset = (c - (lower32 >> 8)) * (lower32 & 0x7f);  // delta * increment
        boolean isCompressible = (lower32 & 0x80) != 0;
        return Collation.incThreeBytePrimaryByOffset(p, isCompressible, offset);
    }

    /**
     * Returns the unassigned-character implicit primary weight for any valid code point c.
     */
    static long unassignedPrimaryFromCodePoint(int c) {
        // Create a gap before U+0000. Use c=-1 for [first unassigned].
        ++c;
        // Fourth byte: 18 values, every 14th byte value (gap of 13).
        long primary = 2 + (c % 18) * 14;
        c /= 18;
        // Third byte: 254 values.
        primary |= (2 + (c % 254)) << 8;
        c /= 254;
        // Second byte: 251 values 04..FE excluding the primary compression bytes.
        primary |= (4 + (c % 251)) << 16;
        // One lead byte covers all code points (c < 0x1182B4 = 1*251*254*18).
        return primary | ((long)UNASSIGNED_IMPLICIT_BYTE << 24);
    }

    static long unassignedCEFromCodePoint(int c) {
        return makeCE(unassignedPrimaryFromCodePoint(c));
    }

    // private Collation()  // No instantiation.
}