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diff --git a/intl/icu/source/i18n/utf16collationiterator.h b/intl/icu/source/i18n/utf16collationiterator.h
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+++ b/intl/icu/source/i18n/utf16collationiterator.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.
+*******************************************************************************
+* utf16collationiterator.h
+*
+* created on: 2010oct27
+* created by: Markus W. Scherer
+*/
+
+#ifndef __UTF16COLLATIONITERATOR_H__
+#define __UTF16COLLATIONITERATOR_H__
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_COLLATION
+
+#include "cmemory.h"
+#include "collation.h"
+#include "collationdata.h"
+#include "collationiterator.h"
+#include "normalizer2impl.h"
+
+U_NAMESPACE_BEGIN
+
+/**
+ * UTF-16 collation element and character iterator.
+ * Handles normalized UTF-16 text inline, with length or NUL-terminated.
+ * Unnormalized text is handled by a subclass.
+ */
+class U_I18N_API UTF16CollationIterator : public CollationIterator {
+public:
+    UTF16CollationIterator(const CollationData *d, UBool numeric,
+                           const char16_t *s, const char16_t *p, const char16_t *lim)
+            : CollationIterator(d, numeric),
+              start(s), pos(p), limit(lim) {}
+
+    UTF16CollationIterator(const UTF16CollationIterator &other, const char16_t *newText);
+
+    virtual ~UTF16CollationIterator();
+
+    virtual bool operator==(const CollationIterator &other) const override;
+
+    virtual void resetToOffset(int32_t newOffset) override;
+
+    virtual int32_t getOffset() const override;
+
+    void setText(const char16_t *s, const char16_t *lim) {
+        reset();
+        start = pos = s;
+        limit = lim;
+    }
+
+    virtual UChar32 nextCodePoint(UErrorCode &errorCode) override;
+
+    virtual UChar32 previousCodePoint(UErrorCode &errorCode) override;
+
+protected:
+    // Copy constructor only for subclasses which set the pointers.
+    UTF16CollationIterator(const UTF16CollationIterator &other)
+            : CollationIterator(other),
+              start(nullptr), pos(nullptr), limit(nullptr) {}
+
+    virtual uint32_t handleNextCE32(UChar32 &c, UErrorCode &errorCode) override;
+
+    virtual char16_t handleGetTrailSurrogate() override;
+
+    virtual UBool foundNULTerminator() override;
+
+    virtual void forwardNumCodePoints(int32_t num, UErrorCode &errorCode) override;
+
+    virtual void backwardNumCodePoints(int32_t num, UErrorCode &errorCode) override;
+
+    // UTF-16 string pointers.
+    // limit can be nullptr for NUL-terminated strings.
+    const char16_t *start, *pos, *limit;
+};
+
+/**
+ * Incrementally checks the input text for FCD and normalizes where necessary.
+ */
+class U_I18N_API FCDUTF16CollationIterator : public UTF16CollationIterator {
+public:
+    FCDUTF16CollationIterator(const CollationData *data, UBool numeric,
+                              const char16_t *s, const char16_t *p, const char16_t *lim)
+            : UTF16CollationIterator(data, numeric, s, p, lim),
+              rawStart(s), segmentStart(p), segmentLimit(nullptr), rawLimit(lim),
+              nfcImpl(data->nfcImpl),
+              checkDir(1) {}
+
+    FCDUTF16CollationIterator(const FCDUTF16CollationIterator &other, const char16_t *newText);
+
+    virtual ~FCDUTF16CollationIterator();
+
+    virtual bool operator==(const CollationIterator &other) const override;
+
+    virtual void resetToOffset(int32_t newOffset) override;
+
+    virtual int32_t getOffset() const override;
+
+    virtual UChar32 nextCodePoint(UErrorCode &errorCode) override;
+
+    virtual UChar32 previousCodePoint(UErrorCode &errorCode) override;
+
+protected:
+    virtual uint32_t handleNextCE32(UChar32 &c, UErrorCode &errorCode) override;
+
+    virtual UBool foundNULTerminator() override;
+
+    virtual void forwardNumCodePoints(int32_t num, UErrorCode &errorCode) override;
+
+    virtual void backwardNumCodePoints(int32_t num, UErrorCode &errorCode) override;
+
+private:
+    /**
+     * Switches to forward checking if possible.
+     * To be called when checkDir < 0 || (checkDir == 0 && pos == limit).
+     * Returns with checkDir > 0 || (checkDir == 0 && pos != limit).
+     */
+    void switchToForward();
+
+    /**
+     * Extend the FCD text segment forward or normalize around pos.
+     * To be called when checkDir > 0 && pos != limit.
+     * @return true if success, checkDir == 0 and pos != limit
+     */
+    UBool nextSegment(UErrorCode &errorCode);
+
+    /**
+     * Switches to backward checking.
+     * To be called when checkDir > 0 || (checkDir == 0 && pos == start).
+     * Returns with checkDir < 0 || (checkDir == 0 && pos != start).
+     */
+    void switchToBackward();
+
+    /**
+     * Extend the FCD text segment backward or normalize around pos.
+     * To be called when checkDir < 0 && pos != start.
+     * @return true if success, checkDir == 0 and pos != start
+     */
+    UBool previousSegment(UErrorCode &errorCode);
+
+    UBool normalize(const char16_t *from, const char16_t *to, UErrorCode &errorCode);
+
+    // Text pointers: The input text is [rawStart, rawLimit[
+    // where rawLimit can be nullptr for NUL-terminated text.
+    //
+    // checkDir > 0:
+    //
+    // The input text [segmentStart..pos[ passes the FCD check.
+    // Moving forward checks incrementally.
+    // segmentLimit is undefined. limit == rawLimit.
+    //
+    // checkDir < 0:
+    // The input text [pos..segmentLimit[ passes the FCD check.
+    // Moving backward checks incrementally.
+    // segmentStart is undefined, start == rawStart.
+    //
+    // checkDir == 0:
+    //
+    // The input text [segmentStart..segmentLimit[ is being processed.
+    // These pointers are at FCD boundaries.
+    // Either this text segment already passes the FCD check
+    // and segmentStart==start<=pos<=limit==segmentLimit,
+    // or the current segment had to be normalized so that
+    // [segmentStart..segmentLimit[ turned into the normalized string,
+    // corresponding to normalized.getBuffer()==start<=pos<=limit==start+normalized.length().
+    const char16_t *rawStart;
+    const char16_t *segmentStart;
+    const char16_t *segmentLimit;
+    // rawLimit==nullptr for a NUL-terminated string.
+    const char16_t *rawLimit;
+
+    const Normalizer2Impl &nfcImpl;
+    UnicodeString normalized;
+    // Direction of incremental FCD check. See comments before rawStart.
+    int8_t checkDir;
+};
+
+U_NAMESPACE_END
+
+#endif  // !UCONFIG_NO_COLLATION
+#endif  // __UTF16COLLATIONITERATOR_H__