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diff --git a/intl/icu/source/i18n/collationiterator.h b/intl/icu/source/i18n/collationiterator.h
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+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+*******************************************************************************
+* Copyright (C) 2010-2014, International Business Machines
+* Corporation and others.  All Rights Reserved.
+*******************************************************************************
+* collationiterator.h
+*
+* created on: 2010oct27
+* created by: Markus W. Scherer
+*/
+
+#ifndef __COLLATIONITERATOR_H__
+#define __COLLATIONITERATOR_H__
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_COLLATION
+
+#include "cmemory.h"
+#include "collation.h"
+#include "collationdata.h"
+
+U_NAMESPACE_BEGIN
+
+class SkippedState;
+class UCharsTrie;
+class UVector32;
+
+/* Large enough for CEs of most short strings. */
+#define CEBUFFER_INITIAL_CAPACITY 40
+
+// Export an explicit template instantiation of the MaybeStackArray that
+//    is used as a data member of CEBuffer.
+//
+//    When building DLLs for Windows this is required even though
+//    no direct access to the MaybeStackArray leaks out of the i18n library.
+//
+// See digitlst.h, pluralaffix.h, datefmt.h, and others for similar examples.
+//
+#if U_PF_WINDOWS <= U_PLATFORM && U_PLATFORM <= U_PF_CYGWIN
+template class U_I18N_API MaybeStackArray<int64_t, CEBUFFER_INITIAL_CAPACITY>;
+#endif
+
+/**
+ * Collation element iterator and abstract character iterator.
+ *
+ * When a method returns a code point value, it must be in 0..10FFFF,
+ * except it can be negative as a sentinel value.
+ */
+class U_I18N_API CollationIterator : public UObject {
+private:
+    class U_I18N_API CEBuffer {
+    private:
+        /** Large enough for CEs of most short strings. */
+        static const int32_t INITIAL_CAPACITY = CEBUFFER_INITIAL_CAPACITY;
+    public:
+        CEBuffer() : length(0) {}
+        ~CEBuffer();
+
+        inline void append(int64_t ce, UErrorCode &errorCode) {
+            if(length < INITIAL_CAPACITY || ensureAppendCapacity(1, errorCode)) {
+                buffer[length++] = ce;
+            }
+        }
+
+        inline void appendUnsafe(int64_t ce) {
+            buffer[length++] = ce;
+        }
+
+        UBool ensureAppendCapacity(int32_t appCap, UErrorCode &errorCode);
+
+        inline UBool incLength(UErrorCode &errorCode) {
+            // Use INITIAL_CAPACITY for a very simple fastpath.
+            // (Rather than buffer.getCapacity().)
+            if(length < INITIAL_CAPACITY || ensureAppendCapacity(1, errorCode)) {
+                ++length;
+                return true;
+            } else {
+                return false;
+            }
+        }
+
+        inline int64_t set(int32_t i, int64_t ce) {
+            return buffer[i] = ce;
+        }
+        inline int64_t get(int32_t i) const { return buffer[i]; }
+
+        const int64_t *getCEs() const { return buffer.getAlias(); }
+
+        int32_t length;
+
+    private:
+        CEBuffer(const CEBuffer &) = delete;
+        void operator=(const CEBuffer &) = delete;
+
+        MaybeStackArray<int64_t, INITIAL_CAPACITY> buffer;
+    };
+
+public:
+    CollationIterator(const CollationData *d, UBool numeric)
+            : trie(d->trie),
+              data(d),
+              cesIndex(0),
+              skipped(nullptr),
+              numCpFwd(-1),
+              isNumeric(numeric) {}
+
+    virtual ~CollationIterator();
+
+    virtual bool operator==(const CollationIterator &other) const;
+    inline bool operator!=(const CollationIterator &other) const {
+        return !operator==(other);
+    }
+
+    /**
+     * Resets the iterator state and sets the position to the specified offset.
+     * Subclasses must implement, and must call the parent class method,
+     * or CollationIterator::reset().
+     */
+    virtual void resetToOffset(int32_t newOffset) = 0;
+
+    virtual int32_t getOffset() const = 0;
+
+    /**
+     * Returns the next collation element.
+     */
+    inline int64_t nextCE(UErrorCode &errorCode) {
+        if(cesIndex < ceBuffer.length) {
+            // Return the next buffered CE.
+            return ceBuffer.get(cesIndex++);
+        }
+        // assert cesIndex == ceBuffer.length;
+        if(!ceBuffer.incLength(errorCode)) {
+            return Collation::NO_CE;
+        }
+        UChar32 c;
+        uint32_t ce32 = handleNextCE32(c, errorCode);
+        uint32_t t = ce32 & 0xff;
+        if(t < Collation::SPECIAL_CE32_LOW_BYTE) {  // Forced-inline of isSpecialCE32(ce32).
+            // Normal CE from the main data.
+            // Forced-inline of ceFromSimpleCE32(ce32).
+            return ceBuffer.set(cesIndex++,
+                    ((int64_t)(ce32 & 0xffff0000) << 32) | ((ce32 & 0xff00) << 16) | (t << 8));
+        }
+        const CollationData *d;
+        // The compiler should be able to optimize the previous and the following
+        // comparisons of t with the same constant.
+        if(t == Collation::SPECIAL_CE32_LOW_BYTE) {
+            if(c < 0) {
+                return ceBuffer.set(cesIndex++, Collation::NO_CE);
+            }
+            d = data->base;
+            ce32 = d->getCE32(c);
+            t = ce32 & 0xff;
+            if(t < Collation::SPECIAL_CE32_LOW_BYTE) {
+                // Normal CE from the base data.
+                return ceBuffer.set(cesIndex++,
+                        ((int64_t)(ce32 & 0xffff0000) << 32) | ((ce32 & 0xff00) << 16) | (t << 8));
+            }
+        } else {
+            d = data;
+        }
+        if(t == Collation::LONG_PRIMARY_CE32_LOW_BYTE) {
+            // Forced-inline of ceFromLongPrimaryCE32(ce32).
+            return ceBuffer.set(cesIndex++,
+                    ((int64_t)(ce32 - t) << 32) | Collation::COMMON_SEC_AND_TER_CE);
+        }
+        return nextCEFromCE32(d, c, ce32, errorCode);
+    }
+
+    /**
+     * Fetches all CEs.
+     * @return getCEsLength()
+     */
+    int32_t fetchCEs(UErrorCode &errorCode);
+
+    /**
+     * Overwrites the current CE (the last one returned by nextCE()).
+     */
+    void setCurrentCE(int64_t ce) {
+        // assert cesIndex > 0;
+        ceBuffer.set(cesIndex - 1, ce);
+    }
+
+    /**
+     * Returns the previous collation element.
+     */
+    int64_t previousCE(UVector32 &offsets, UErrorCode &errorCode);
+
+    inline int32_t getCEsLength() const {
+        return ceBuffer.length;
+    }
+
+    inline int64_t getCE(int32_t i) const {
+        return ceBuffer.get(i);
+    }
+
+    const int64_t *getCEs() const {
+        return ceBuffer.getCEs();
+    }
+
+    void clearCEs() {
+        cesIndex = ceBuffer.length = 0;
+    }
+
+    void clearCEsIfNoneRemaining() {
+        if(cesIndex == ceBuffer.length) { clearCEs(); }
+    }
+
+    /**
+     * Returns the next code point (with post-increment).
+     * Public for identical-level comparison and for testing.
+     */
+    virtual UChar32 nextCodePoint(UErrorCode &errorCode) = 0;
+
+    /**
+     * Returns the previous code point (with pre-decrement).
+     * Public for identical-level comparison and for testing.
+     */
+    virtual UChar32 previousCodePoint(UErrorCode &errorCode) = 0;
+
+protected:
+    CollationIterator(const CollationIterator &other);
+
+    void reset();
+
+    /**
+     * Returns the next code point and its local CE32 value.
+     * Returns Collation::FALLBACK_CE32 at the end of the text (c<0)
+     * or when c's CE32 value is to be looked up in the base data (fallback).
+     *
+     * The code point is used for fallbacks, context and implicit weights.
+     * It is ignored when the returned CE32 is not special (e.g., FFFD_CE32).
+     */
+    virtual uint32_t handleNextCE32(UChar32 &c, UErrorCode &errorCode);
+
+    /**
+     * Called when handleNextCE32() returns a LEAD_SURROGATE_TAG for a lead surrogate code unit.
+     * Returns the trail surrogate in that case and advances past it,
+     * if a trail surrogate follows the lead surrogate.
+     * Otherwise returns any other code unit and does not advance.
+     */
+    virtual char16_t handleGetTrailSurrogate();
+
+    /**
+     * Called when handleNextCE32() returns with c==0, to see whether it is a NUL terminator.
+     * (Not needed in Java.)
+     */
+    virtual UBool foundNULTerminator();
+
+    /**
+     * @return false if surrogate code points U+D800..U+DFFF
+     *         map to their own implicit primary weights (for UTF-16),
+     *         or true if they map to CE(U+FFFD) (for UTF-8)
+     */
+    virtual UBool forbidSurrogateCodePoints() const;
+
+    virtual void forwardNumCodePoints(int32_t num, UErrorCode &errorCode) = 0;
+
+    virtual void backwardNumCodePoints(int32_t num, UErrorCode &errorCode) = 0;
+
+    /**
+     * Returns the CE32 from the data trie.
+     * Normally the same as data->getCE32(), but overridden in the builder.
+     * Call this only when the faster data->getCE32() cannot be used.
+     */
+    virtual uint32_t getDataCE32(UChar32 c) const;
+
+    virtual uint32_t getCE32FromBuilderData(uint32_t ce32, UErrorCode &errorCode);
+
+    void appendCEsFromCE32(const CollationData *d, UChar32 c, uint32_t ce32,
+                           UBool forward, UErrorCode &errorCode);
+
+    // Main lookup trie of the data object.
+    const UTrie2 *trie;
+    const CollationData *data;
+
+private:
+    int64_t nextCEFromCE32(const CollationData *d, UChar32 c, uint32_t ce32,
+                           UErrorCode &errorCode);
+
+    uint32_t getCE32FromPrefix(const CollationData *d, uint32_t ce32,
+                               UErrorCode &errorCode);
+
+    UChar32 nextSkippedCodePoint(UErrorCode &errorCode);
+
+    void backwardNumSkipped(int32_t n, UErrorCode &errorCode);
+
+    uint32_t nextCE32FromContraction(
+            const CollationData *d, uint32_t contractionCE32,
+            const char16_t *p, uint32_t ce32, UChar32 c,
+            UErrorCode &errorCode);
+
+    uint32_t nextCE32FromDiscontiguousContraction(
+            const CollationData *d, UCharsTrie &suffixes, uint32_t ce32,
+            int32_t lookAhead, UChar32 c,
+            UErrorCode &errorCode);
+
+    /**
+     * Returns the previous CE when data->isUnsafeBackward(c, isNumeric).
+     */
+    int64_t previousCEUnsafe(UChar32 c, UVector32 &offsets, UErrorCode &errorCode);
+
+    /**
+     * Turns a string of digits (bytes 0..9)
+     * into a sequence of CEs that will sort in numeric order.
+     *
+     * Starts from this ce32's digit value and consumes the following/preceding digits.
+     * The digits string must not be empty and must not have leading zeros.
+     */
+    void appendNumericCEs(uint32_t ce32, UBool forward, UErrorCode &errorCode);
+
+    /**
+     * Turns 1..254 digits into a sequence of CEs.
+     * Called by appendNumericCEs() for each segment of at most 254 digits.
+     */
+    void appendNumericSegmentCEs(const char *digits, int32_t length, UErrorCode &errorCode);
+
+    CEBuffer ceBuffer;
+    int32_t cesIndex;
+
+    SkippedState *skipped;
+
+    // Number of code points to read forward, or -1.
+    // Used as a forward iteration limit in previousCEUnsafe().
+    int32_t numCpFwd;
+    // Numeric collation (CollationSettings::NUMERIC).
+    UBool isNumeric;
+};
+
+U_NAMESPACE_END
+
+#endif  // !UCONFIG_NO_COLLATION
+#endif  // __COLLATIONITERATOR_H__