Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1723 insertions, 0 deletions

diff --git a/intl/icu/source/i18n/collationbuilder.cpp b/intl/icu/source/i18n/collationbuilder.cpp
new file mode 100644
index 0000000000..d8fb89738c
--- /dev/null
+++ b/intl/icu/source/i18n/collationbuilder.cpp
@@ -0,0 +1,1723 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+*******************************************************************************
+* Copyright (C) 2013-2014, International Business Machines
+* Corporation and others.  All Rights Reserved.
+*******************************************************************************
+* collationbuilder.cpp
+*
+* (replaced the former ucol_bld.cpp)
+*
+* created on: 2013may06
+* created by: Markus W. Scherer
+*/
+
+#ifdef DEBUG_COLLATION_BUILDER
+#include <stdio.h>
+#endif
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_COLLATION
+
+#include "unicode/caniter.h"
+#include "unicode/normalizer2.h"
+#include "unicode/tblcoll.h"
+#include "unicode/parseerr.h"
+#include "unicode/uchar.h"
+#include "unicode/ucol.h"
+#include "unicode/unistr.h"
+#include "unicode/usetiter.h"
+#include "unicode/utf16.h"
+#include "unicode/uversion.h"
+#include "cmemory.h"
+#include "collation.h"
+#include "collationbuilder.h"
+#include "collationdata.h"
+#include "collationdatabuilder.h"
+#include "collationfastlatin.h"
+#include "collationroot.h"
+#include "collationrootelements.h"
+#include "collationruleparser.h"
+#include "collationsettings.h"
+#include "collationtailoring.h"
+#include "collationweights.h"
+#include "normalizer2impl.h"
+#include "uassert.h"
+#include "ucol_imp.h"
+#include "utf16collationiterator.h"
+
+U_NAMESPACE_BEGIN
+
+namespace {
+
+class BundleImporter : public CollationRuleParser::Importer {
+public:
+    BundleImporter() {}
+    virtual ~BundleImporter();
+    virtual void getRules(
+            const char *localeID, const char *collationType,
+            UnicodeString &rules,
+            const char *&errorReason, UErrorCode &errorCode) override;
+};
+
+BundleImporter::~BundleImporter() {}
+
+void
+BundleImporter::getRules(
+        const char *localeID, const char *collationType,
+        UnicodeString &rules,
+        const char *& /*errorReason*/, UErrorCode &errorCode) {
+    CollationLoader::loadRules(localeID, collationType, rules, errorCode);
+}
+
+}  // namespace
+
+// RuleBasedCollator implementation ---------------------------------------- ***
+
+// These methods are here, rather than in rulebasedcollator.cpp,
+// for modularization:
+// Most code using Collator does not need to build a Collator from rules.
+// By moving these constructors and helper methods to a separate file,
+// most code will not have a static dependency on the builder code.
+
+RuleBasedCollator::RuleBasedCollator()
+        : data(nullptr),
+          settings(nullptr),
+          tailoring(nullptr),
+          cacheEntry(nullptr),
+          validLocale(""),
+          explicitlySetAttributes(0),
+          actualLocaleIsSameAsValid(false) {
+}
+
+RuleBasedCollator::RuleBasedCollator(const UnicodeString &rules, UErrorCode &errorCode)
+        : data(nullptr),
+          settings(nullptr),
+          tailoring(nullptr),
+          cacheEntry(nullptr),
+          validLocale(""),
+          explicitlySetAttributes(0),
+          actualLocaleIsSameAsValid(false) {
+    internalBuildTailoring(rules, UCOL_DEFAULT, UCOL_DEFAULT, nullptr, nullptr, errorCode);
+}
+
+RuleBasedCollator::RuleBasedCollator(const UnicodeString &rules, ECollationStrength strength,
+                                     UErrorCode &errorCode)
+        : data(nullptr),
+          settings(nullptr),
+          tailoring(nullptr),
+          cacheEntry(nullptr),
+          validLocale(""),
+          explicitlySetAttributes(0),
+          actualLocaleIsSameAsValid(false) {
+    internalBuildTailoring(rules, strength, UCOL_DEFAULT, nullptr, nullptr, errorCode);
+}
+
+RuleBasedCollator::RuleBasedCollator(const UnicodeString &rules,
+                                     UColAttributeValue decompositionMode,
+                                     UErrorCode &errorCode)
+        : data(nullptr),
+          settings(nullptr),
+          tailoring(nullptr),
+          cacheEntry(nullptr),
+          validLocale(""),
+          explicitlySetAttributes(0),
+          actualLocaleIsSameAsValid(false) {
+    internalBuildTailoring(rules, UCOL_DEFAULT, decompositionMode, nullptr, nullptr, errorCode);
+}
+
+RuleBasedCollator::RuleBasedCollator(const UnicodeString &rules,
+                                     ECollationStrength strength,
+                                     UColAttributeValue decompositionMode,
+                                     UErrorCode &errorCode)
+        : data(nullptr),
+          settings(nullptr),
+          tailoring(nullptr),
+          cacheEntry(nullptr),
+          validLocale(""),
+          explicitlySetAttributes(0),
+          actualLocaleIsSameAsValid(false) {
+    internalBuildTailoring(rules, strength, decompositionMode, nullptr, nullptr, errorCode);
+}
+
+RuleBasedCollator::RuleBasedCollator(const UnicodeString &rules,
+                                     UParseError &parseError, UnicodeString &reason,
+                                     UErrorCode &errorCode)
+        : data(nullptr),
+          settings(nullptr),
+          tailoring(nullptr),
+          cacheEntry(nullptr),
+          validLocale(""),
+          explicitlySetAttributes(0),
+          actualLocaleIsSameAsValid(false) {
+    internalBuildTailoring(rules, UCOL_DEFAULT, UCOL_DEFAULT, &parseError, &reason, errorCode);
+}
+
+void
+RuleBasedCollator::internalBuildTailoring(const UnicodeString &rules,
+                                          int32_t strength,
+                                          UColAttributeValue decompositionMode,
+                                          UParseError *outParseError, UnicodeString *outReason,
+                                          UErrorCode &errorCode) {
+    const CollationTailoring *base = CollationRoot::getRoot(errorCode);
+    if(U_FAILURE(errorCode)) { return; }
+    if(outReason != nullptr) { outReason->remove(); }
+    CollationBuilder builder(base, errorCode);
+    UVersionInfo noVersion = { 0, 0, 0, 0 };
+    BundleImporter importer;
+    LocalPointer<CollationTailoring> t(builder.parseAndBuild(rules, noVersion,
+                                                             &importer,
+                                                             outParseError, errorCode));
+    if(U_FAILURE(errorCode)) {
+        const char *reason = builder.getErrorReason();
+        if(reason != nullptr && outReason != nullptr) {
+            *outReason = UnicodeString(reason, -1, US_INV);
+        }
+        return;
+    }
+    t->actualLocale.setToBogus();
+    adoptTailoring(t.orphan(), errorCode);
+    // Set attributes after building the collator,
+    // to keep the default settings consistent with the rule string.
+    if(strength != UCOL_DEFAULT) {
+        setAttribute(UCOL_STRENGTH, (UColAttributeValue)strength, errorCode);
+    }
+    if(decompositionMode != UCOL_DEFAULT) {
+        setAttribute(UCOL_NORMALIZATION_MODE, decompositionMode, errorCode);
+    }
+}
+
+// CollationBuilder implementation ----------------------------------------- ***
+
+CollationBuilder::CollationBuilder(const CollationTailoring *b, UBool icu4xMode, UErrorCode &errorCode)
+        : nfd(*Normalizer2::getNFDInstance(errorCode)),
+          fcd(*Normalizer2Factory::getFCDInstance(errorCode)),
+          nfcImpl(*Normalizer2Factory::getNFCImpl(errorCode)),
+          base(b),
+          baseData(b->data),
+          rootElements(b->data->rootElements, b->data->rootElementsLength),
+          variableTop(0),
+          dataBuilder(new CollationDataBuilder(icu4xMode, errorCode)), fastLatinEnabled(true),
+          icu4xMode(icu4xMode),
+          errorReason(nullptr),
+          cesLength(0),
+          rootPrimaryIndexes(errorCode), nodes(errorCode) {
+    nfcImpl.ensureCanonIterData(errorCode);
+    if(U_FAILURE(errorCode)) {
+        errorReason = "CollationBuilder fields initialization failed";
+        return;
+    }
+    if(dataBuilder == nullptr) {
+        errorCode = U_MEMORY_ALLOCATION_ERROR;
+        return;
+    }
+    dataBuilder->initForTailoring(baseData, errorCode);
+    if(U_FAILURE(errorCode)) {
+        errorReason = "CollationBuilder initialization failed";
+    }
+}
+
+CollationBuilder::CollationBuilder(const CollationTailoring *b, UErrorCode &errorCode)
+  : CollationBuilder(b, false, errorCode)
+{}
+
+CollationBuilder::~CollationBuilder() {
+    delete dataBuilder;
+}
+
+CollationTailoring *
+CollationBuilder::parseAndBuild(const UnicodeString &ruleString,
+                                const UVersionInfo rulesVersion,
+                                CollationRuleParser::Importer *importer,
+                                UParseError *outParseError,
+                                UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return nullptr; }
+    if(baseData->rootElements == nullptr) {
+        errorCode = U_MISSING_RESOURCE_ERROR;
+        errorReason = "missing root elements data, tailoring not supported";
+        return nullptr;
+    }
+    LocalPointer<CollationTailoring> tailoring(new CollationTailoring(base->settings));
+    if(tailoring.isNull() || tailoring->isBogus()) {
+        errorCode = U_MEMORY_ALLOCATION_ERROR;
+        return nullptr;
+    }
+    CollationRuleParser parser(baseData, errorCode);
+    if(U_FAILURE(errorCode)) { return nullptr; }
+    // Note: This always bases &[last variable] and &[first regular]
+    // on the root collator's maxVariable/variableTop.
+    // If we wanted this to change after [maxVariable x], then we would keep
+    // the tailoring.settings pointer here and read its variableTop when we need it.
+    // See http://unicode.org/cldr/trac/ticket/6070
+    variableTop = base->settings->variableTop;
+    parser.setSink(this);
+    parser.setImporter(importer);
+    CollationSettings &ownedSettings = *SharedObject::copyOnWrite(tailoring->settings);
+    parser.parse(ruleString, ownedSettings, outParseError, errorCode);
+    errorReason = parser.getErrorReason();
+    if(U_FAILURE(errorCode)) { return nullptr; }
+    if(dataBuilder->hasMappings()) {
+        makeTailoredCEs(errorCode);
+        if (!icu4xMode) {
+            closeOverComposites(errorCode);
+        }
+        finalizeCEs(errorCode);
+        if (!icu4xMode) {
+            // Copy all of ASCII, and Latin-1 letters, into each tailoring.
+            optimizeSet.add(0, 0x7f);
+            optimizeSet.add(0xc0, 0xff);
+            // Hangul is decomposed on the fly during collation,
+            // and the tailoring data is always built with HANGUL_TAG specials.
+            optimizeSet.remove(Hangul::HANGUL_BASE, Hangul::HANGUL_END);
+            dataBuilder->optimize(optimizeSet, errorCode);
+        }
+        tailoring->ensureOwnedData(errorCode);
+        if(U_FAILURE(errorCode)) { return nullptr; }
+        if(fastLatinEnabled) { dataBuilder->enableFastLatin(); }
+        dataBuilder->build(*tailoring->ownedData, errorCode);
+        tailoring->builder = dataBuilder;
+        dataBuilder = nullptr;
+    } else {
+        tailoring->data = baseData;
+    }
+    if(U_FAILURE(errorCode)) { return nullptr; }
+    ownedSettings.fastLatinOptions = CollationFastLatin::getOptions(
+        tailoring->data, ownedSettings,
+        ownedSettings.fastLatinPrimaries, UPRV_LENGTHOF(ownedSettings.fastLatinPrimaries));
+    tailoring->rules = ruleString;
+    tailoring->rules.getTerminatedBuffer();  // ensure NUL-termination
+    tailoring->setVersion(base->version, rulesVersion);
+    return tailoring.orphan();
+}
+
+void
+CollationBuilder::addReset(int32_t strength, const UnicodeString &str,
+                           const char *&parserErrorReason, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+    U_ASSERT(!str.isEmpty());
+    if(str.charAt(0) == CollationRuleParser::POS_LEAD) {
+        ces[0] = getSpecialResetPosition(str, parserErrorReason, errorCode);
+        cesLength = 1;
+        if(U_FAILURE(errorCode)) { return; }
+        U_ASSERT((ces[0] & Collation::CASE_AND_QUATERNARY_MASK) == 0);
+    } else {
+        // normal reset to a character or string
+        UnicodeString nfdString = nfd.normalize(str, errorCode);
+        if(U_FAILURE(errorCode)) {
+            parserErrorReason = "normalizing the reset position";
+            return;
+        }
+        cesLength = dataBuilder->getCEs(nfdString, ces, 0);
+        if(cesLength > Collation::MAX_EXPANSION_LENGTH) {
+            errorCode = U_ILLEGAL_ARGUMENT_ERROR;
+            parserErrorReason = "reset position maps to too many collation elements (more than 31)";
+            return;
+        }
+    }
+    if(strength == UCOL_IDENTICAL) { return; }  // simple reset-at-position
+
+    // &[before strength]position
+    U_ASSERT(UCOL_PRIMARY <= strength && strength <= UCOL_TERTIARY);
+    int32_t index = findOrInsertNodeForCEs(strength, parserErrorReason, errorCode);
+    if(U_FAILURE(errorCode)) { return; }
+
+    int64_t node = nodes.elementAti(index);
+    // If the index is for a "weaker" node,
+    // then skip backwards over this and further "weaker" nodes.
+    while(strengthFromNode(node) > strength) {
+        index = previousIndexFromNode(node);
+        node = nodes.elementAti(index);
+    }
+
+    // Find or insert a node whose index we will put into a temporary CE.
+    if(strengthFromNode(node) == strength && isTailoredNode(node)) {
+        // Reset to just before this same-strength tailored node.
+        index = previousIndexFromNode(node);
+    } else if(strength == UCOL_PRIMARY) {
+        // root primary node (has no previous index)
+        uint32_t p = weight32FromNode(node);
+        if(p == 0) {
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "reset primary-before ignorable not possible";
+            return;
+        }
+        if(p <= rootElements.getFirstPrimary()) {
+            // There is no primary gap between ignorables and the space-first-primary.
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "reset primary-before first non-ignorable not supported";
+            return;
+        }
+        if(p == Collation::FIRST_TRAILING_PRIMARY) {
+            // We do not support tailoring to an unassigned-implicit CE.
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "reset primary-before [first trailing] not supported";
+            return;
+        }
+        p = rootElements.getPrimaryBefore(p, baseData->isCompressiblePrimary(p));
+        index = findOrInsertNodeForPrimary(p, errorCode);
+        // Go to the last node in this list:
+        // Tailor after the last node between adjacent root nodes.
+        for(;;) {
+            node = nodes.elementAti(index);
+            int32_t nextIndex = nextIndexFromNode(node);
+            if(nextIndex == 0) { break; }
+            index = nextIndex;
+        }
+    } else {
+        // &[before 2] or &[before 3]
+        index = findCommonNode(index, UCOL_SECONDARY);
+        if(strength >= UCOL_TERTIARY) {
+            index = findCommonNode(index, UCOL_TERTIARY);
+        }
+        // findCommonNode() stayed on the stronger node or moved to
+        // an explicit common-weight node of the reset-before strength.
+        node = nodes.elementAti(index);
+        if(strengthFromNode(node) == strength) {
+            // Found a same-strength node with an explicit weight.
+            uint32_t weight16 = weight16FromNode(node);
+            if(weight16 == 0) {
+                errorCode = U_UNSUPPORTED_ERROR;
+                if(strength == UCOL_SECONDARY) {
+                    parserErrorReason = "reset secondary-before secondary ignorable not possible";
+                } else {
+                    parserErrorReason = "reset tertiary-before completely ignorable not possible";
+                }
+                return;
+            }
+            U_ASSERT(weight16 > Collation::BEFORE_WEIGHT16);
+            // Reset to just before this node.
+            // Insert the preceding same-level explicit weight if it is not there already.
+            // Which explicit weight immediately precedes this one?
+            weight16 = getWeight16Before(index, node, strength);
+            // Does this preceding weight have a node?
+            uint32_t previousWeight16;
+            int32_t previousIndex = previousIndexFromNode(node);
+            for(int32_t i = previousIndex;; i = previousIndexFromNode(node)) {
+                node = nodes.elementAti(i);
+                int32_t previousStrength = strengthFromNode(node);
+                if(previousStrength < strength) {
+                    U_ASSERT(weight16 >= Collation::COMMON_WEIGHT16 || i == previousIndex);
+                    // Either the reset element has an above-common weight and
+                    // the parent node provides the implied common weight,
+                    // or the reset element has a weight<=common in the node
+                    // right after the parent, and we need to insert the preceding weight.
+                    previousWeight16 = Collation::COMMON_WEIGHT16;
+                    break;
+                } else if(previousStrength == strength && !isTailoredNode(node)) {
+                    previousWeight16 = weight16FromNode(node);
+                    break;
+                }
+                // Skip weaker nodes and same-level tailored nodes.
+            }
+            if(previousWeight16 == weight16) {
+                // The preceding weight has a node,
+                // maybe with following weaker or tailored nodes.
+                // Reset to the last of them.
+                index = previousIndex;
+            } else {
+                // Insert a node with the preceding weight, reset to that.
+                node = nodeFromWeight16(weight16) | nodeFromStrength(strength);
+                index = insertNodeBetween(previousIndex, index, node, errorCode);
+            }
+        } else {
+            // Found a stronger node with implied strength-common weight.
+            uint32_t weight16 = getWeight16Before(index, node, strength);
+            index = findOrInsertWeakNode(index, weight16, strength, errorCode);
+        }
+        // Strength of the temporary CE = strength of its reset position.
+        // Code above raises an error if the before-strength is stronger.
+        strength = ceStrength(ces[cesLength - 1]);
+    }
+    if(U_FAILURE(errorCode)) {
+        parserErrorReason = "inserting reset position for &[before n]";
+        return;
+    }
+    ces[cesLength - 1] = tempCEFromIndexAndStrength(index, strength);
+}
+
+uint32_t
+CollationBuilder::getWeight16Before(int32_t index, int64_t node, int32_t level) {
+    U_ASSERT(strengthFromNode(node) < level || !isTailoredNode(node));
+    // Collect the root CE weights if this node is for a root CE.
+    // If it is not, then return the low non-primary boundary for a tailored CE.
+    uint32_t t;
+    if(strengthFromNode(node) == UCOL_TERTIARY) {
+        t = weight16FromNode(node);
+    } else {
+        t = Collation::COMMON_WEIGHT16;  // Stronger node with implied common weight.
+    }
+    while(strengthFromNode(node) > UCOL_SECONDARY) {
+        index = previousIndexFromNode(node);
+        node = nodes.elementAti(index);
+    }
+    if(isTailoredNode(node)) {
+        return Collation::BEFORE_WEIGHT16;
+    }
+    uint32_t s;
+    if(strengthFromNode(node) == UCOL_SECONDARY) {
+        s = weight16FromNode(node);
+    } else {
+        s = Collation::COMMON_WEIGHT16;  // Stronger node with implied common weight.
+    }
+    while(strengthFromNode(node) > UCOL_PRIMARY) {
+        index = previousIndexFromNode(node);
+        node = nodes.elementAti(index);
+    }
+    if(isTailoredNode(node)) {
+        return Collation::BEFORE_WEIGHT16;
+    }
+    // [p, s, t] is a root CE. Return the preceding weight for the requested level.
+    uint32_t p = weight32FromNode(node);
+    uint32_t weight16;
+    if(level == UCOL_SECONDARY) {
+        weight16 = rootElements.getSecondaryBefore(p, s);
+    } else {
+        weight16 = rootElements.getTertiaryBefore(p, s, t);
+        U_ASSERT((weight16 & ~Collation::ONLY_TERTIARY_MASK) == 0);
+    }
+    return weight16;
+}
+
+int64_t
+CollationBuilder::getSpecialResetPosition(const UnicodeString &str,
+                                          const char *&parserErrorReason, UErrorCode &errorCode) {
+    U_ASSERT(str.length() == 2);
+    int64_t ce;
+    int32_t strength = UCOL_PRIMARY;
+    UBool isBoundary = false;
+    UChar32 pos = str.charAt(1) - CollationRuleParser::POS_BASE;
+    U_ASSERT(0 <= pos && pos <= CollationRuleParser::LAST_TRAILING);
+    switch(pos) {
+    case CollationRuleParser::FIRST_TERTIARY_IGNORABLE:
+        // Quaternary CEs are not supported.
+        // Non-zero quaternary weights are possible only on tertiary or stronger CEs.
+        return 0;
+    case CollationRuleParser::LAST_TERTIARY_IGNORABLE:
+        return 0;
+    case CollationRuleParser::FIRST_SECONDARY_IGNORABLE: {
+        // Look for a tailored tertiary node after [0, 0, 0].
+        int32_t index = findOrInsertNodeForRootCE(0, UCOL_TERTIARY, errorCode);
+        if(U_FAILURE(errorCode)) { return 0; }
+        int64_t node = nodes.elementAti(index);
+        if((index = nextIndexFromNode(node)) != 0) {
+            node = nodes.elementAti(index);
+            U_ASSERT(strengthFromNode(node) <= UCOL_TERTIARY);
+            if(isTailoredNode(node) && strengthFromNode(node) == UCOL_TERTIARY) {
+                return tempCEFromIndexAndStrength(index, UCOL_TERTIARY);
+            }
+        }
+        return rootElements.getFirstTertiaryCE();
+        // No need to look for nodeHasAnyBefore() on a tertiary node.
+    }
+    case CollationRuleParser::LAST_SECONDARY_IGNORABLE:
+        ce = rootElements.getLastTertiaryCE();
+        strength = UCOL_TERTIARY;
+        break;
+    case CollationRuleParser::FIRST_PRIMARY_IGNORABLE: {
+        // Look for a tailored secondary node after [0, 0, *].
+        int32_t index = findOrInsertNodeForRootCE(0, UCOL_SECONDARY, errorCode);
+        if(U_FAILURE(errorCode)) { return 0; }
+        int64_t node = nodes.elementAti(index);
+        while((index = nextIndexFromNode(node)) != 0) {
+            node = nodes.elementAti(index);
+            strength = strengthFromNode(node);
+            if(strength < UCOL_SECONDARY) { break; }
+            if(strength == UCOL_SECONDARY) {
+                if(isTailoredNode(node)) {
+                    if(nodeHasBefore3(node)) {
+                        index = nextIndexFromNode(nodes.elementAti(nextIndexFromNode(node)));
+                        U_ASSERT(isTailoredNode(nodes.elementAti(index)));
+                    }
+                    return tempCEFromIndexAndStrength(index, UCOL_SECONDARY);
+                } else {
+                    break;
+                }
+            }
+        }
+        ce = rootElements.getFirstSecondaryCE();
+        strength = UCOL_SECONDARY;
+        break;
+    }
+    case CollationRuleParser::LAST_PRIMARY_IGNORABLE:
+        ce = rootElements.getLastSecondaryCE();
+        strength = UCOL_SECONDARY;
+        break;
+    case CollationRuleParser::FIRST_VARIABLE:
+        ce = rootElements.getFirstPrimaryCE();
+        isBoundary = true;  // FractionalUCA.txt: FDD1 00A0, SPACE first primary
+        break;
+    case CollationRuleParser::LAST_VARIABLE:
+        ce = rootElements.lastCEWithPrimaryBefore(variableTop + 1);
+        break;
+    case CollationRuleParser::FIRST_REGULAR:
+        ce = rootElements.firstCEWithPrimaryAtLeast(variableTop + 1);
+        isBoundary = true;  // FractionalUCA.txt: FDD1 263A, SYMBOL first primary
+        break;
+    case CollationRuleParser::LAST_REGULAR:
+        // Use the Hani-first-primary rather than the actual last "regular" CE before it,
+        // for backward compatibility with behavior before the introduction of
+        // script-first-primary CEs in the root collator.
+        ce = rootElements.firstCEWithPrimaryAtLeast(
+            baseData->getFirstPrimaryForGroup(USCRIPT_HAN));
+        break;
+    case CollationRuleParser::FIRST_IMPLICIT:
+        ce = baseData->getSingleCE(0x4e00, errorCode);
+        break;
+    case CollationRuleParser::LAST_IMPLICIT:
+        // We do not support tailoring to an unassigned-implicit CE.
+        errorCode = U_UNSUPPORTED_ERROR;
+        parserErrorReason = "reset to [last implicit] not supported";
+        return 0;
+    case CollationRuleParser::FIRST_TRAILING:
+        ce = Collation::makeCE(Collation::FIRST_TRAILING_PRIMARY);
+        isBoundary = true;  // trailing first primary (there is no mapping for it)
+        break;
+    case CollationRuleParser::LAST_TRAILING:
+        errorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        parserErrorReason = "LDML forbids tailoring to U+FFFF";
+        return 0;
+    default:
+        UPRV_UNREACHABLE_EXIT;
+    }
+
+    int32_t index = findOrInsertNodeForRootCE(ce, strength, errorCode);
+    if(U_FAILURE(errorCode)) { return 0; }
+    int64_t node = nodes.elementAti(index);
+    if((pos & 1) == 0) {
+        // even pos = [first xyz]
+        if(!nodeHasAnyBefore(node) && isBoundary) {
+            // A <group> first primary boundary is artificially added to FractionalUCA.txt.
+            // It is reachable via its special contraction, but is not normally used.
+            // Find the first character tailored after the boundary CE,
+            // or the first real root CE after it.
+            if((index = nextIndexFromNode(node)) != 0) {
+                // If there is a following node, then it must be tailored
+                // because there are no root CEs with a boundary primary
+                // and non-common secondary/tertiary weights.
+                node = nodes.elementAti(index);
+                U_ASSERT(isTailoredNode(node));
+                ce = tempCEFromIndexAndStrength(index, strength);
+            } else {
+                U_ASSERT(strength == UCOL_PRIMARY);
+                uint32_t p = (uint32_t)(ce >> 32);
+                int32_t pIndex = rootElements.findPrimary(p);
+                UBool isCompressible = baseData->isCompressiblePrimary(p);
+                p = rootElements.getPrimaryAfter(p, pIndex, isCompressible);
+                ce = Collation::makeCE(p);
+                index = findOrInsertNodeForRootCE(ce, UCOL_PRIMARY, errorCode);
+                if(U_FAILURE(errorCode)) { return 0; }
+                node = nodes.elementAti(index);
+            }
+        }
+        if(nodeHasAnyBefore(node)) {
+            // Get the first node that was tailored before this one at a weaker strength.
+            if(nodeHasBefore2(node)) {
+                index = nextIndexFromNode(nodes.elementAti(nextIndexFromNode(node)));
+                node = nodes.elementAti(index);
+            }
+            if(nodeHasBefore3(node)) {
+                index = nextIndexFromNode(nodes.elementAti(nextIndexFromNode(node)));
+            }
+            U_ASSERT(isTailoredNode(nodes.elementAti(index)));
+            ce = tempCEFromIndexAndStrength(index, strength);
+        }
+    } else {
+        // odd pos = [last xyz]
+        // Find the last node that was tailored after the [last xyz]
+        // at a strength no greater than the position's strength.
+        for(;;) {
+            int32_t nextIndex = nextIndexFromNode(node);
+            if(nextIndex == 0) { break; }
+            int64_t nextNode = nodes.elementAti(nextIndex);
+            if(strengthFromNode(nextNode) < strength) { break; }
+            index = nextIndex;
+            node = nextNode;
+        }
+        // Do not make a temporary CE for a root node.
+        // This last node might be the node for the root CE itself,
+        // or a node with a common secondary or tertiary weight.
+        if(isTailoredNode(node)) {
+            ce = tempCEFromIndexAndStrength(index, strength);
+        }
+    }
+    return ce;
+}
+
+void
+CollationBuilder::addRelation(int32_t strength, const UnicodeString &prefix,
+                              const UnicodeString &str, const UnicodeString &extension,
+                              const char *&parserErrorReason, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+    UnicodeString nfdPrefix;
+    if(!prefix.isEmpty()) {
+        nfd.normalize(prefix, nfdPrefix, errorCode);
+        if(U_FAILURE(errorCode)) {
+            parserErrorReason = "normalizing the relation prefix";
+            return;
+        }
+    }
+    UnicodeString nfdString = nfd.normalize(str, errorCode);
+    if(U_FAILURE(errorCode)) {
+        parserErrorReason = "normalizing the relation string";
+        return;
+    }
+
+    // The runtime code decomposes Hangul syllables on the fly,
+    // with recursive processing but without making the Jamo pieces visible for matching.
+    // It does not work with certain types of contextual mappings.
+    int32_t nfdLength = nfdString.length();
+    if(nfdLength >= 2) {
+        char16_t c = nfdString.charAt(0);
+        if(Hangul::isJamoL(c) || Hangul::isJamoV(c)) {
+            // While handling a Hangul syllable, contractions starting with Jamo L or V
+            // would not see the following Jamo of that syllable.
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "contractions starting with conjoining Jamo L or V not supported";
+            return;
+        }
+        c = nfdString.charAt(nfdLength - 1);
+        if(Hangul::isJamoL(c) ||
+                (Hangul::isJamoV(c) && Hangul::isJamoL(nfdString.charAt(nfdLength - 2)))) {
+            // A contraction ending with Jamo L or L+V would require
+            // generating Hangul syllables in addTailComposites() (588 for a Jamo L),
+            // or decomposing a following Hangul syllable on the fly, during contraction matching.
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "contractions ending with conjoining Jamo L or L+V not supported";
+            return;
+        }
+        // A Hangul syllable completely inside a contraction is ok.
+    }
+    // Note: If there is a prefix, then the parser checked that
+    // both the prefix and the string begin with NFC boundaries (not Jamo V or T).
+    // Therefore: prefix.isEmpty() || !isJamoVOrT(nfdString.charAt(0))
+    // (While handling a Hangul syllable, prefixes on Jamo V or T
+    // would not see the previous Jamo of that syllable.)
+
+    if(strength != UCOL_IDENTICAL) {
+        // Find the node index after which we insert the new tailored node.
+        int32_t index = findOrInsertNodeForCEs(strength, parserErrorReason, errorCode);
+        U_ASSERT(cesLength > 0);
+        int64_t ce = ces[cesLength - 1];
+        if(strength == UCOL_PRIMARY && !isTempCE(ce) && (uint32_t)(ce >> 32) == 0) {
+            // There is no primary gap between ignorables and the space-first-primary.
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "tailoring primary after ignorables not supported";
+            return;
+        }
+        if(strength == UCOL_QUATERNARY && ce == 0) {
+            // The CE data structure does not support non-zero quaternary weights
+            // on tertiary ignorables.
+            errorCode = U_UNSUPPORTED_ERROR;
+            parserErrorReason = "tailoring quaternary after tertiary ignorables not supported";
+            return;
+        }
+        // Insert the new tailored node.
+        index = insertTailoredNodeAfter(index, strength, errorCode);
+        if(U_FAILURE(errorCode)) {
+            parserErrorReason = "modifying collation elements";
+            return;
+        }
+        // Strength of the temporary CE:
+        // The new relation may yield a stronger CE but not a weaker one.
+        int32_t tempStrength = ceStrength(ce);
+        if(strength < tempStrength) { tempStrength = strength; }
+        ces[cesLength - 1] = tempCEFromIndexAndStrength(index, tempStrength);
+    }
+
+    setCaseBits(nfdString, parserErrorReason, errorCode);
+    if(U_FAILURE(errorCode)) { return; }
+
+    int32_t cesLengthBeforeExtension = cesLength;
+    if(!extension.isEmpty()) {
+        UnicodeString nfdExtension = nfd.normalize(extension, errorCode);
+        if(U_FAILURE(errorCode)) {
+            parserErrorReason = "normalizing the relation extension";
+            return;
+        }
+        cesLength = dataBuilder->getCEs(nfdExtension, ces, cesLength);
+        if(cesLength > Collation::MAX_EXPANSION_LENGTH) {
+            errorCode = U_ILLEGAL_ARGUMENT_ERROR;
+            parserErrorReason =
+                "extension string adds too many collation elements (more than 31 total)";
+            return;
+        }
+    }
+    uint32_t ce32 = Collation::UNASSIGNED_CE32;
+    if(!icu4xMode && (prefix != nfdPrefix || str != nfdString) &&
+            !ignorePrefix(prefix, errorCode) && !ignoreString(str, errorCode)) {
+        // Map from the original input to the CEs.
+        // We do this in case the canonical closure is incomplete,
+        // so that it is possible to explicitly provide the missing mappings.
+        ce32 = addIfDifferent(prefix, str, ces, cesLength, ce32, errorCode);
+    }
+    if (!icu4xMode) {
+        addWithClosure(nfdPrefix, nfdString, ces, cesLength, ce32, errorCode);
+    } else {
+        addIfDifferent(nfdPrefix, nfdString, ces, cesLength, ce32, errorCode);
+    }
+    if(U_FAILURE(errorCode)) {
+        parserErrorReason = "writing collation elements";
+        return;
+    }
+    cesLength = cesLengthBeforeExtension;
+}
+
+int32_t
+CollationBuilder::findOrInsertNodeForCEs(int32_t strength, const char *&parserErrorReason,
+                                         UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return 0; }
+    U_ASSERT(UCOL_PRIMARY <= strength && strength <= UCOL_QUATERNARY);
+
+    // Find the last CE that is at least as "strong" as the requested difference.
+    // Note: Stronger is smaller (UCOL_PRIMARY=0).
+    int64_t ce;
+    for(;; --cesLength) {
+        if(cesLength == 0) {
+            ce = ces[0] = 0;
+            cesLength = 1;
+            break;
+        } else {
+            ce = ces[cesLength - 1];
+        }
+        if(ceStrength(ce) <= strength) { break; }
+    }
+
+    if(isTempCE(ce)) {
+        // No need to findCommonNode() here for lower levels
+        // because insertTailoredNodeAfter() will do that anyway.
+        return indexFromTempCE(ce);
+    }
+
+    // root CE
+    if((uint8_t)(ce >> 56) == Collation::UNASSIGNED_IMPLICIT_BYTE) {
+        errorCode = U_UNSUPPORTED_ERROR;
+        parserErrorReason = "tailoring relative to an unassigned code point not supported";
+        return 0;
+    }
+    return findOrInsertNodeForRootCE(ce, strength, errorCode);
+}
+
+int32_t
+CollationBuilder::findOrInsertNodeForRootCE(int64_t ce, int32_t strength, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return 0; }
+    U_ASSERT((uint8_t)(ce >> 56) != Collation::UNASSIGNED_IMPLICIT_BYTE);
+
+    // Find or insert the node for each of the root CE's weights,
+    // down to the requested level/strength.
+    // Root CEs must have common=zero quaternary weights (for which we never insert any nodes).
+    U_ASSERT((ce & 0xc0) == 0);
+    int32_t index = findOrInsertNodeForPrimary((uint32_t)(ce >> 32), errorCode);
+    if(strength >= UCOL_SECONDARY) {
+        uint32_t lower32 = (uint32_t)ce;
+        index = findOrInsertWeakNode(index, lower32 >> 16, UCOL_SECONDARY, errorCode);
+        if(strength >= UCOL_TERTIARY) {
+            index = findOrInsertWeakNode(index, lower32 & Collation::ONLY_TERTIARY_MASK,
+                                         UCOL_TERTIARY, errorCode);
+        }
+    }
+    return index;
+}
+
+namespace {
+
+/**
+ * Like Java Collections.binarySearch(List, key, Comparator).
+ *
+ * @return the index>=0 where the item was found,
+ *         or the index<0 for inserting the string at ~index in sorted order
+ *         (index into rootPrimaryIndexes)
+ */
+int32_t
+binarySearchForRootPrimaryNode(const int32_t *rootPrimaryIndexes, int32_t length,
+                               const int64_t *nodes, uint32_t p) {
+    if(length == 0) { return ~0; }
+    int32_t start = 0;
+    int32_t limit = length;
+    for (;;) {
+        int32_t i = (start + limit) / 2;
+        int64_t node = nodes[rootPrimaryIndexes[i]];
+        uint32_t nodePrimary = (uint32_t)(node >> 32);  // weight32FromNode(node)
+        if (p == nodePrimary) {
+            return i;
+        } else if (p < nodePrimary) {
+            if (i == start) {
+                return ~start;  // insert s before i
+            }
+            limit = i;
+        } else {
+            if (i == start) {
+                return ~(start + 1);  // insert s after i
+            }
+            start = i;
+        }
+    }
+}
+
+}  // namespace
+
+int32_t
+CollationBuilder::findOrInsertNodeForPrimary(uint32_t p, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return 0; }
+
+    int32_t rootIndex = binarySearchForRootPrimaryNode(
+        rootPrimaryIndexes.getBuffer(), rootPrimaryIndexes.size(), nodes.getBuffer(), p);
+    if(rootIndex >= 0) {
+        return rootPrimaryIndexes.elementAti(rootIndex);
+    } else {
+        // Start a new list of nodes with this primary.
+        int32_t index = nodes.size();
+        nodes.addElement(nodeFromWeight32(p), errorCode);
+        rootPrimaryIndexes.insertElementAt(index, ~rootIndex, errorCode);
+        return index;
+    }
+}
+
+int32_t
+CollationBuilder::findOrInsertWeakNode(int32_t index, uint32_t weight16, int32_t level, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return 0; }
+    U_ASSERT(0 <= index && index < nodes.size());
+    U_ASSERT(UCOL_SECONDARY <= level && level <= UCOL_TERTIARY);
+
+    if(weight16 == Collation::COMMON_WEIGHT16) {
+        return findCommonNode(index, level);
+    }
+
+    // If this will be the first below-common weight for the parent node,
+    // then we will also need to insert a common weight after it.
+    int64_t node = nodes.elementAti(index);
+    U_ASSERT(strengthFromNode(node) < level);  // parent node is stronger
+    if(weight16 != 0 && weight16 < Collation::COMMON_WEIGHT16) {
+        int32_t hasThisLevelBefore = level == UCOL_SECONDARY ? HAS_BEFORE2 : HAS_BEFORE3;
+        if((node & hasThisLevelBefore) == 0) {
+            // The parent node has an implied level-common weight.
+            int64_t commonNode =
+                nodeFromWeight16(Collation::COMMON_WEIGHT16) | nodeFromStrength(level);
+            if(level == UCOL_SECONDARY) {
+                // Move the HAS_BEFORE3 flag from the parent node
+                // to the new secondary common node.
+                commonNode |= node & HAS_BEFORE3;
+                node &= ~(int64_t)HAS_BEFORE3;
+            }
+            nodes.setElementAt(node | hasThisLevelBefore, index);
+            // Insert below-common-weight node.
+            int32_t nextIndex = nextIndexFromNode(node);
+            node = nodeFromWeight16(weight16) | nodeFromStrength(level);
+            index = insertNodeBetween(index, nextIndex, node, errorCode);
+            // Insert common-weight node.
+            insertNodeBetween(index, nextIndex, commonNode, errorCode);
+            // Return index of below-common-weight node.
+            return index;
+        }
+    }
+
+    // Find the root CE's weight for this level.
+    // Postpone insertion if not found:
+    // Insert the new root node before the next stronger node,
+    // or before the next root node with the same strength and a larger weight.
+    int32_t nextIndex;
+    while((nextIndex = nextIndexFromNode(node)) != 0) {
+        node = nodes.elementAti(nextIndex);
+        int32_t nextStrength = strengthFromNode(node);
+        if(nextStrength <= level) {
+            // Insert before a stronger node.
+            if(nextStrength < level) { break; }
+            // nextStrength == level
+            if(!isTailoredNode(node)) {
+                uint32_t nextWeight16 = weight16FromNode(node);
+                if(nextWeight16 == weight16) {
+                    // Found the node for the root CE up to this level.
+                    return nextIndex;
+                }
+                // Insert before a node with a larger same-strength weight.
+                if(nextWeight16 > weight16) { break; }
+            }
+        }
+        // Skip the next node.
+        index = nextIndex;
+    }
+    node = nodeFromWeight16(weight16) | nodeFromStrength(level);
+    return insertNodeBetween(index, nextIndex, node, errorCode);
+}
+
+int32_t
+CollationBuilder::insertTailoredNodeAfter(int32_t index, int32_t strength, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return 0; }
+    U_ASSERT(0 <= index && index < nodes.size());
+    if(strength >= UCOL_SECONDARY) {
+        index = findCommonNode(index, UCOL_SECONDARY);
+        if(strength >= UCOL_TERTIARY) {
+            index = findCommonNode(index, UCOL_TERTIARY);
+        }
+    }
+    // Postpone insertion:
+    // Insert the new node before the next one with a strength at least as strong.
+    int64_t node = nodes.elementAti(index);
+    int32_t nextIndex;
+    while((nextIndex = nextIndexFromNode(node)) != 0) {
+        node = nodes.elementAti(nextIndex);
+        if(strengthFromNode(node) <= strength) { break; }
+        // Skip the next node which has a weaker (larger) strength than the new one.
+        index = nextIndex;
+    }
+    node = IS_TAILORED | nodeFromStrength(strength);
+    return insertNodeBetween(index, nextIndex, node, errorCode);
+}
+
+int32_t
+CollationBuilder::insertNodeBetween(int32_t index, int32_t nextIndex, int64_t node,
+                                    UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return 0; }
+    U_ASSERT(previousIndexFromNode(node) == 0);
+    U_ASSERT(nextIndexFromNode(node) == 0);
+    U_ASSERT(nextIndexFromNode(nodes.elementAti(index)) == nextIndex);
+    // Append the new node and link it to the existing nodes.
+    int32_t newIndex = nodes.size();
+    node |= nodeFromPreviousIndex(index) | nodeFromNextIndex(nextIndex);
+    nodes.addElement(node, errorCode);
+    if(U_FAILURE(errorCode)) { return 0; }
+    // nodes[index].nextIndex = newIndex
+    node = nodes.elementAti(index);
+    nodes.setElementAt(changeNodeNextIndex(node, newIndex), index);
+    // nodes[nextIndex].previousIndex = newIndex
+    if(nextIndex != 0) {
+        node = nodes.elementAti(nextIndex);
+        nodes.setElementAt(changeNodePreviousIndex(node, newIndex), nextIndex);
+    }
+    return newIndex;
+}
+
+int32_t
+CollationBuilder::findCommonNode(int32_t index, int32_t strength) const {
+    U_ASSERT(UCOL_SECONDARY <= strength && strength <= UCOL_TERTIARY);
+    int64_t node = nodes.elementAti(index);
+    if(strengthFromNode(node) >= strength) {
+        // The current node is no stronger.
+        return index;
+    }
+    if(strength == UCOL_SECONDARY ? !nodeHasBefore2(node) : !nodeHasBefore3(node)) {
+        // The current node implies the strength-common weight.
+        return index;
+    }
+    index = nextIndexFromNode(node);
+    node = nodes.elementAti(index);
+    U_ASSERT(!isTailoredNode(node) && strengthFromNode(node) == strength &&
+            weight16FromNode(node) < Collation::COMMON_WEIGHT16);
+    // Skip to the explicit common node.
+    do {
+        index = nextIndexFromNode(node);
+        node = nodes.elementAti(index);
+        U_ASSERT(strengthFromNode(node) >= strength);
+    } while(isTailoredNode(node) || strengthFromNode(node) > strength ||
+            weight16FromNode(node) < Collation::COMMON_WEIGHT16);
+    U_ASSERT(weight16FromNode(node) == Collation::COMMON_WEIGHT16);
+    return index;
+}
+
+void
+CollationBuilder::setCaseBits(const UnicodeString &nfdString,
+                              const char *&parserErrorReason, UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+    int32_t numTailoredPrimaries = 0;
+    for(int32_t i = 0; i < cesLength; ++i) {
+        if(ceStrength(ces[i]) == UCOL_PRIMARY) { ++numTailoredPrimaries; }
+    }
+    // We should not be able to get too many case bits because
+    // cesLength<=31==MAX_EXPANSION_LENGTH.
+    // 31 pairs of case bits fit into an int64_t without setting its sign bit.
+    U_ASSERT(numTailoredPrimaries <= 31);
+
+    int64_t cases = 0;
+    if(numTailoredPrimaries > 0) {
+        const char16_t *s = nfdString.getBuffer();
+        UTF16CollationIterator baseCEs(baseData, false, s, s, s + nfdString.length());
+        int32_t baseCEsLength = baseCEs.fetchCEs(errorCode) - 1;
+        if(U_FAILURE(errorCode)) {
+            parserErrorReason = "fetching root CEs for tailored string";
+            return;
+        }
+        U_ASSERT(baseCEsLength >= 0 && baseCEs.getCE(baseCEsLength) == Collation::NO_CE);
+
+        uint32_t lastCase = 0;
+        int32_t numBasePrimaries = 0;
+        for(int32_t i = 0; i < baseCEsLength; ++i) {
+            int64_t ce = baseCEs.getCE(i);
+            if((ce >> 32) != 0) {
+                ++numBasePrimaries;
+                uint32_t c = ((uint32_t)ce >> 14) & 3;
+                U_ASSERT(c == 0 || c == 2);  // lowercase or uppercase, no mixed case in any base CE
+                if(numBasePrimaries < numTailoredPrimaries) {
+                    cases |= (int64_t)c << ((numBasePrimaries - 1) * 2);
+                } else if(numBasePrimaries == numTailoredPrimaries) {
+                    lastCase = c;
+                } else if(c != lastCase) {
+                    // There are more base primary CEs than tailored primaries.
+                    // Set mixed case if the case bits of the remainder differ.
+                    lastCase = 1;
+                    // Nothing more can change.
+                    break;
+                }
+            }
+        }
+        if(numBasePrimaries >= numTailoredPrimaries) {
+            cases |= (int64_t)lastCase << ((numTailoredPrimaries - 1) * 2);
+        }
+    }
+
+    for(int32_t i = 0; i < cesLength; ++i) {
+        int64_t ce = ces[i] & INT64_C(0xffffffffffff3fff);  // clear old case bits
+        int32_t strength = ceStrength(ce);
+        if(strength == UCOL_PRIMARY) {
+            ce |= (cases & 3) << 14;
+            cases >>= 2;
+        } else if(strength == UCOL_TERTIARY) {
+            // Tertiary CEs must have uppercase bits.
+            // See the LDML spec, and comments in class CollationCompare.
+            ce |= 0x8000;
+        }
+        // Tertiary ignorable CEs must have 0 case bits.
+        // We set 0 case bits for secondary CEs too
+        // since currently only U+0345 is cased and maps to a secondary CE,
+        // and it is lowercase. Other secondaries are uncased.
+        // See [[:Cased:]&[:uca1=:]] where uca1 queries the root primary weight.
+        ces[i] = ce;
+    }
+}
+
+void
+CollationBuilder::suppressContractions(const UnicodeSet &set, const char *&parserErrorReason,
+                                       UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+    dataBuilder->suppressContractions(set, errorCode);
+    if(U_FAILURE(errorCode)) {
+        parserErrorReason = "application of [suppressContractions [set]] failed";
+    }
+}
+
+void
+CollationBuilder::optimize(const UnicodeSet &set, const char *& /* parserErrorReason */,
+                           UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+    optimizeSet.addAll(set);
+}
+
+uint32_t
+CollationBuilder::addWithClosure(const UnicodeString &nfdPrefix, const UnicodeString &nfdString,
+                                 const int64_t newCEs[], int32_t newCEsLength, uint32_t ce32,
+                                 UErrorCode &errorCode) {
+    // Map from the NFD input to the CEs.
+    ce32 = addIfDifferent(nfdPrefix, nfdString, newCEs, newCEsLength, ce32, errorCode);
+    ce32 = addOnlyClosure(nfdPrefix, nfdString, newCEs, newCEsLength, ce32, errorCode);
+    addTailComposites(nfdPrefix, nfdString, errorCode);
+    return ce32;
+}
+
+uint32_t
+CollationBuilder::addOnlyClosure(const UnicodeString &nfdPrefix, const UnicodeString &nfdString,
+                                 const int64_t newCEs[], int32_t newCEsLength, uint32_t ce32,
+                                 UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return ce32; }
+
+    // Map from canonically equivalent input to the CEs. (But not from the all-NFD input.)
+    if(nfdPrefix.isEmpty()) {
+        CanonicalIterator stringIter(nfdString, errorCode);
+        if(U_FAILURE(errorCode)) { return ce32; }
+        UnicodeString prefix;
+        for(;;) {
+            UnicodeString str = stringIter.next();
+            if(str.isBogus()) { break; }
+            if(ignoreString(str, errorCode) || str == nfdString) { continue; }
+            ce32 = addIfDifferent(prefix, str, newCEs, newCEsLength, ce32, errorCode);
+            if(U_FAILURE(errorCode)) { return ce32; }
+        }
+    } else {
+        CanonicalIterator prefixIter(nfdPrefix, errorCode);
+        CanonicalIterator stringIter(nfdString, errorCode);
+        if(U_FAILURE(errorCode)) { return ce32; }
+        for(;;) {
+            UnicodeString prefix = prefixIter.next();
+            if(prefix.isBogus()) { break; }
+            if(ignorePrefix(prefix, errorCode)) { continue; }
+            UBool samePrefix = prefix == nfdPrefix;
+            for(;;) {
+                UnicodeString str = stringIter.next();
+                if(str.isBogus()) { break; }
+                if(ignoreString(str, errorCode) || (samePrefix && str == nfdString)) { continue; }
+                ce32 = addIfDifferent(prefix, str, newCEs, newCEsLength, ce32, errorCode);
+                if(U_FAILURE(errorCode)) { return ce32; }
+            }
+            stringIter.reset();
+        }
+    }
+    return ce32;
+}
+
+void
+CollationBuilder::addTailComposites(const UnicodeString &nfdPrefix, const UnicodeString &nfdString,
+                                    UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+
+    // Look for the last starter in the NFD string.
+    UChar32 lastStarter;
+    int32_t indexAfterLastStarter = nfdString.length();
+    for(;;) {
+        if(indexAfterLastStarter == 0) { return; }  // no starter at all
+        lastStarter = nfdString.char32At(indexAfterLastStarter - 1);
+        if(nfd.getCombiningClass(lastStarter) == 0) { break; }
+        indexAfterLastStarter -= U16_LENGTH(lastStarter);
+    }
+    // No closure to Hangul syllables since we decompose them on the fly.
+    if(Hangul::isJamoL(lastStarter)) { return; }
+
+    // Are there any composites whose decomposition starts with the lastStarter?
+    // Note: Normalizer2Impl does not currently return start sets for NFC_QC=Maybe characters.
+    // We might find some more equivalent mappings here if it did.
+    UnicodeSet composites;
+    if(!nfcImpl.getCanonStartSet(lastStarter, composites)) { return; }
+
+    UnicodeString decomp;
+    UnicodeString newNFDString, newString;
+    int64_t newCEs[Collation::MAX_EXPANSION_LENGTH];
+    UnicodeSetIterator iter(composites);
+    while(iter.next()) {
+        U_ASSERT(!iter.isString());
+        UChar32 composite = iter.getCodepoint();
+        nfd.getDecomposition(composite, decomp);
+        if(!mergeCompositeIntoString(nfdString, indexAfterLastStarter, composite, decomp,
+                                     newNFDString, newString, errorCode)) {
+            continue;
+        }
+        int32_t newCEsLength = dataBuilder->getCEs(nfdPrefix, newNFDString, newCEs, 0);
+        if(newCEsLength > Collation::MAX_EXPANSION_LENGTH) {
+            // Ignore mappings that we cannot store.
+            continue;
+        }
+        // Note: It is possible that the newCEs do not make use of the mapping
+        // for which we are adding the tail composites, in which case we might be adding
+        // unnecessary mappings.
+        // For example, when we add tail composites for ae^ (^=combining circumflex),
+        // UCA discontiguous-contraction matching does not find any matches
+        // for ae_^ (_=any combining diacritic below) *unless* there is also
+        // a contraction mapping for ae.
+        // Thus, if there is no ae contraction, then the ae^ mapping is ignored
+        // while fetching the newCEs for ae_^.
+        // TODO: Try to detect this effectively.
+        // (Alternatively, print a warning when prefix contractions are missing.)
+
+        // We do not need an explicit mapping for the NFD strings.
+        // It is fine if the NFD input collates like this via a sequence of mappings.
+        // It also saves a little bit of space, and may reduce the set of characters with contractions.
+        uint32_t ce32 = addIfDifferent(nfdPrefix, newString,
+                                       newCEs, newCEsLength, Collation::UNASSIGNED_CE32, errorCode);
+        if(ce32 != Collation::UNASSIGNED_CE32) {
+            // was different, was added
+            addOnlyClosure(nfdPrefix, newNFDString, newCEs, newCEsLength, ce32, errorCode);
+        }
+    }
+}
+
+UBool
+CollationBuilder::mergeCompositeIntoString(const UnicodeString &nfdString,
+                                           int32_t indexAfterLastStarter,
+                                           UChar32 composite, const UnicodeString &decomp,
+                                           UnicodeString &newNFDString, UnicodeString &newString,
+                                           UErrorCode &errorCode) const {
+    if(U_FAILURE(errorCode)) { return false; }
+    U_ASSERT(nfdString.char32At(indexAfterLastStarter - 1) == decomp.char32At(0));
+    int32_t lastStarterLength = decomp.moveIndex32(0, 1);
+    if(lastStarterLength == decomp.length()) {
+        // Singleton decompositions should be found by addWithClosure()
+        // and the CanonicalIterator, so we can ignore them here.
+        return false;
+    }
+    if(nfdString.compare(indexAfterLastStarter, 0x7fffffff,
+                         decomp, lastStarterLength, 0x7fffffff) == 0) {
+        // same strings, nothing new to be found here
+        return false;
+    }
+
+    // Make new FCD strings that combine a composite, or its decomposition,
+    // into the nfdString's last starter and the combining marks following it.
+    // Make an NFD version, and a version with the composite.
+    newNFDString.setTo(nfdString, 0, indexAfterLastStarter);
+    newString.setTo(nfdString, 0, indexAfterLastStarter - lastStarterLength).append(composite);
+
+    // The following is related to discontiguous contraction matching,
+    // but builds only FCD strings (or else returns false).
+    int32_t sourceIndex = indexAfterLastStarter;
+    int32_t decompIndex = lastStarterLength;
+    // Small optimization: We keep the source character across loop iterations
+    // because we do not always consume it,
+    // and then need not fetch it again nor look up its combining class again.
+    UChar32 sourceChar = U_SENTINEL;
+    // The cc variables need to be declared before the loop so that at the end
+    // they are set to the last combining classes seen.
+    uint8_t sourceCC = 0;
+    uint8_t decompCC = 0;
+    for(;;) {
+        if(sourceChar < 0) {
+            if(sourceIndex >= nfdString.length()) { break; }
+            sourceChar = nfdString.char32At(sourceIndex);
+            sourceCC = nfd.getCombiningClass(sourceChar);
+            U_ASSERT(sourceCC != 0);
+        }
+        // We consume a decomposition character in each iteration.
+        if(decompIndex >= decomp.length()) { break; }
+        UChar32 decompChar = decomp.char32At(decompIndex);
+        decompCC = nfd.getCombiningClass(decompChar);
+        // Compare the two characters and their combining classes.
+        if(decompCC == 0) {
+            // Unable to merge because the source contains a non-zero combining mark
+            // but the composite's decomposition contains another starter.
+            // The strings would not be equivalent.
+            return false;
+        } else if(sourceCC < decompCC) {
+            // Composite + sourceChar would not be FCD.
+            return false;
+        } else if(decompCC < sourceCC) {
+            newNFDString.append(decompChar);
+            decompIndex += U16_LENGTH(decompChar);
+        } else if(decompChar != sourceChar) {
+            // Blocked because same combining class.
+            return false;
+        } else {  // match: decompChar == sourceChar
+            newNFDString.append(decompChar);
+            decompIndex += U16_LENGTH(decompChar);
+            sourceIndex += U16_LENGTH(decompChar);
+            sourceChar = U_SENTINEL;
+        }
+    }
+    // We are at the end of at least one of the two inputs.
+    if(sourceChar >= 0) {  // more characters from nfdString but not from decomp
+        if(sourceCC < decompCC) {
+            // Appending the next source character to the composite would not be FCD.
+            return false;
+        }
+        newNFDString.append(nfdString, sourceIndex, 0x7fffffff);
+        newString.append(nfdString, sourceIndex, 0x7fffffff);
+    } else if(decompIndex < decomp.length()) {  // more characters from decomp, not from nfdString
+        newNFDString.append(decomp, decompIndex, 0x7fffffff);
+    }
+    U_ASSERT(nfd.isNormalized(newNFDString, errorCode));
+    U_ASSERT(fcd.isNormalized(newString, errorCode));
+    U_ASSERT(nfd.normalize(newString, errorCode) == newNFDString);  // canonically equivalent
+    return true;
+}
+
+UBool
+CollationBuilder::ignorePrefix(const UnicodeString &s, UErrorCode &errorCode) const {
+    // Do not map non-FCD prefixes.
+    return !isFCD(s, errorCode);
+}
+
+UBool
+CollationBuilder::ignoreString(const UnicodeString &s, UErrorCode &errorCode) const {
+    // Do not map non-FCD strings.
+    // Do not map strings that start with Hangul syllables: We decompose those on the fly.
+    return !isFCD(s, errorCode) || Hangul::isHangul(s.charAt(0));
+}
+
+UBool
+CollationBuilder::isFCD(const UnicodeString &s, UErrorCode &errorCode) const {
+    return U_SUCCESS(errorCode) && fcd.isNormalized(s, errorCode);
+}
+
+void
+CollationBuilder::closeOverComposites(UErrorCode &errorCode) {
+    UnicodeSet composites(UNICODE_STRING_SIMPLE("[:NFD_QC=N:]"), errorCode);  // Java: static final
+    if(U_FAILURE(errorCode)) { return; }
+    // Hangul is decomposed on the fly during collation.
+    composites.remove(Hangul::HANGUL_BASE, Hangul::HANGUL_END);
+    UnicodeString prefix;  // empty
+    UnicodeString nfdString;
+    UnicodeSetIterator iter(composites);
+    while(iter.next()) {
+        U_ASSERT(!iter.isString());
+        nfd.getDecomposition(iter.getCodepoint(), nfdString);
+        cesLength = dataBuilder->getCEs(nfdString, ces, 0);
+        if(cesLength > Collation::MAX_EXPANSION_LENGTH) {
+            // Too many CEs from the decomposition (unusual), ignore this composite.
+            // We could add a capacity parameter to getCEs() and reallocate if necessary.
+            // However, this can only really happen in contrived cases.
+            continue;
+        }
+        const UnicodeString &composite(iter.getString());
+        addIfDifferent(prefix, composite, ces, cesLength, Collation::UNASSIGNED_CE32, errorCode);
+    }
+}
+
+uint32_t
+CollationBuilder::addIfDifferent(const UnicodeString &prefix, const UnicodeString &str,
+                                 const int64_t newCEs[], int32_t newCEsLength, uint32_t ce32,
+                                 UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return ce32; }
+    int64_t oldCEs[Collation::MAX_EXPANSION_LENGTH];
+    int32_t oldCEsLength = dataBuilder->getCEs(prefix, str, oldCEs, 0);
+    if(!sameCEs(newCEs, newCEsLength, oldCEs, oldCEsLength)) {
+        if(ce32 == Collation::UNASSIGNED_CE32) {
+            ce32 = dataBuilder->encodeCEs(newCEs, newCEsLength, errorCode);
+        }
+        dataBuilder->addCE32(prefix, str, ce32, errorCode);
+    }
+    return ce32;
+}
+
+UBool
+CollationBuilder::sameCEs(const int64_t ces1[], int32_t ces1Length,
+                          const int64_t ces2[], int32_t ces2Length) {
+    if(ces1Length != ces2Length) {
+        return false;
+    }
+    U_ASSERT(ces1Length <= Collation::MAX_EXPANSION_LENGTH);
+    for(int32_t i = 0; i < ces1Length; ++i) {
+        if(ces1[i] != ces2[i]) { return false; }
+    }
+    return true;
+}
+
+#ifdef DEBUG_COLLATION_BUILDER
+
+uint32_t
+alignWeightRight(uint32_t w) {
+    if(w != 0) {
+        while((w & 0xff) == 0) { w >>= 8; }
+    }
+    return w;
+}
+
+#endif
+
+void
+CollationBuilder::makeTailoredCEs(UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+
+    CollationWeights primaries, secondaries, tertiaries;
+    int64_t *nodesArray = nodes.getBuffer();
+#ifdef DEBUG_COLLATION_BUILDER
+        puts("\nCollationBuilder::makeTailoredCEs()");
+#endif
+
+    for(int32_t rpi = 0; rpi < rootPrimaryIndexes.size(); ++rpi) {
+        int32_t i = rootPrimaryIndexes.elementAti(rpi);
+        int64_t node = nodesArray[i];
+        uint32_t p = weight32FromNode(node);
+        uint32_t s = p == 0 ? 0 : Collation::COMMON_WEIGHT16;
+        uint32_t t = s;
+        uint32_t q = 0;
+        UBool pIsTailored = false;
+        UBool sIsTailored = false;
+        UBool tIsTailored = false;
+#ifdef DEBUG_COLLATION_BUILDER
+        printf("\nprimary     %lx\n", (long)alignWeightRight(p));
+#endif
+        int32_t pIndex = p == 0 ? 0 : rootElements.findPrimary(p);
+        int32_t nextIndex = nextIndexFromNode(node);
+        while(nextIndex != 0) {
+            i = nextIndex;
+            node = nodesArray[i];
+            nextIndex = nextIndexFromNode(node);
+            int32_t strength = strengthFromNode(node);
+            if(strength == UCOL_QUATERNARY) {
+                U_ASSERT(isTailoredNode(node));
+#ifdef DEBUG_COLLATION_BUILDER
+                printf("      quat+     ");
+#endif
+                if(q == 3) {
+                    errorCode = U_BUFFER_OVERFLOW_ERROR;
+                    errorReason = "quaternary tailoring gap too small";
+                    return;
+                }
+                ++q;
+            } else {
+                if(strength == UCOL_TERTIARY) {
+                    if(isTailoredNode(node)) {
+#ifdef DEBUG_COLLATION_BUILDER
+                        printf("    ter+        ");
+#endif
+                        if(!tIsTailored) {
+                            // First tailored tertiary node for [p, s].
+                            int32_t tCount = countTailoredNodes(nodesArray, nextIndex,
+                                                                UCOL_TERTIARY) + 1;
+                            uint32_t tLimit;
+                            if(t == 0) {
+                                // Gap at the beginning of the tertiary CE range.
+                                t = rootElements.getTertiaryBoundary() - 0x100;
+                                tLimit = rootElements.getFirstTertiaryCE() & Collation::ONLY_TERTIARY_MASK;
+                            } else if(!pIsTailored && !sIsTailored) {
+                                // p and s are root weights.
+                                tLimit = rootElements.getTertiaryAfter(pIndex, s, t);
+                            } else if(t == Collation::BEFORE_WEIGHT16) {
+                                tLimit = Collation::COMMON_WEIGHT16;
+                            } else {
+                                // [p, s] is tailored.
+                                U_ASSERT(t == Collation::COMMON_WEIGHT16);
+                                tLimit = rootElements.getTertiaryBoundary();
+                            }
+                            U_ASSERT(tLimit == 0x4000 || (tLimit & ~Collation::ONLY_TERTIARY_MASK) == 0);
+                            tertiaries.initForTertiary();
+                            if(!tertiaries.allocWeights(t, tLimit, tCount)) {
+                                errorCode = U_BUFFER_OVERFLOW_ERROR;
+                                errorReason = "tertiary tailoring gap too small";
+                                return;
+                            }
+                            tIsTailored = true;
+                        }
+                        t = tertiaries.nextWeight();
+                        U_ASSERT(t != 0xffffffff);
+                    } else {
+                        t = weight16FromNode(node);
+                        tIsTailored = false;
+#ifdef DEBUG_COLLATION_BUILDER
+                        printf("    ter     %lx\n", (long)alignWeightRight(t));
+#endif
+                    }
+                } else {
+                    if(strength == UCOL_SECONDARY) {
+                        if(isTailoredNode(node)) {
+#ifdef DEBUG_COLLATION_BUILDER
+                            printf("  sec+          ");
+#endif
+                            if(!sIsTailored) {
+                                // First tailored secondary node for p.
+                                int32_t sCount = countTailoredNodes(nodesArray, nextIndex,
+                                                                    UCOL_SECONDARY) + 1;
+                                uint32_t sLimit;
+                                if(s == 0) {
+                                    // Gap at the beginning of the secondary CE range.
+                                    s = rootElements.getSecondaryBoundary() - 0x100;
+                                    sLimit = rootElements.getFirstSecondaryCE() >> 16;
+                                } else if(!pIsTailored) {
+                                    // p is a root primary.
+                                    sLimit = rootElements.getSecondaryAfter(pIndex, s);
+                                } else if(s == Collation::BEFORE_WEIGHT16) {
+                                    sLimit = Collation::COMMON_WEIGHT16;
+                                } else {
+                                    // p is a tailored primary.
+                                    U_ASSERT(s == Collation::COMMON_WEIGHT16);
+                                    sLimit = rootElements.getSecondaryBoundary();
+                                }
+                                if(s == Collation::COMMON_WEIGHT16) {
+                                    // Do not tailor into the getSortKey() range of
+                                    // compressed common secondaries.
+                                    s = rootElements.getLastCommonSecondary();
+                                }
+                                secondaries.initForSecondary();
+                                if(!secondaries.allocWeights(s, sLimit, sCount)) {
+                                    errorCode = U_BUFFER_OVERFLOW_ERROR;
+                                    errorReason = "secondary tailoring gap too small";
+#ifdef DEBUG_COLLATION_BUILDER
+                                    printf("!secondaries.allocWeights(%lx, %lx, sCount=%ld)\n",
+                                           (long)alignWeightRight(s), (long)alignWeightRight(sLimit),
+                                           (long)alignWeightRight(sCount));
+#endif
+                                    return;
+                                }
+                                sIsTailored = true;
+                            }
+                            s = secondaries.nextWeight();
+                            U_ASSERT(s != 0xffffffff);
+                        } else {
+                            s = weight16FromNode(node);
+                            sIsTailored = false;
+#ifdef DEBUG_COLLATION_BUILDER
+                            printf("  sec       %lx\n", (long)alignWeightRight(s));
+#endif
+                        }
+                    } else /* UCOL_PRIMARY */ {
+                        U_ASSERT(isTailoredNode(node));
+#ifdef DEBUG_COLLATION_BUILDER
+                        printf("pri+            ");
+#endif
+                        if(!pIsTailored) {
+                            // First tailored primary node in this list.
+                            int32_t pCount = countTailoredNodes(nodesArray, nextIndex,
+                                                                UCOL_PRIMARY) + 1;
+                            UBool isCompressible = baseData->isCompressiblePrimary(p);
+                            uint32_t pLimit =
+                                rootElements.getPrimaryAfter(p, pIndex, isCompressible);
+                            primaries.initForPrimary(isCompressible);
+                            if(!primaries.allocWeights(p, pLimit, pCount)) {
+                                errorCode = U_BUFFER_OVERFLOW_ERROR;  // TODO: introduce a more specific UErrorCode?
+                                errorReason = "primary tailoring gap too small";
+                                return;
+                            }
+                            pIsTailored = true;
+                        }
+                        p = primaries.nextWeight();
+                        U_ASSERT(p != 0xffffffff);
+                        s = Collation::COMMON_WEIGHT16;
+                        sIsTailored = false;
+                    }
+                    t = s == 0 ? 0 : Collation::COMMON_WEIGHT16;
+                    tIsTailored = false;
+                }
+                q = 0;
+            }
+            if(isTailoredNode(node)) {
+                nodesArray[i] = Collation::makeCE(p, s, t, q);
+#ifdef DEBUG_COLLATION_BUILDER
+                printf("%016llx\n", (long long)nodesArray[i]);
+#endif
+            }
+        }
+    }
+}
+
+int32_t
+CollationBuilder::countTailoredNodes(const int64_t *nodesArray, int32_t i, int32_t strength) {
+    int32_t count = 0;
+    for(;;) {
+        if(i == 0) { break; }
+        int64_t node = nodesArray[i];
+        if(strengthFromNode(node) < strength) { break; }
+        if(strengthFromNode(node) == strength) {
+            if(isTailoredNode(node)) {
+                ++count;
+            } else {
+                break;
+            }
+        }
+        i = nextIndexFromNode(node);
+    }
+    return count;
+}
+
+class CEFinalizer : public CollationDataBuilder::CEModifier {
+public:
+    CEFinalizer(const int64_t *ces) : finalCEs(ces) {}
+    virtual ~CEFinalizer();
+    virtual int64_t modifyCE32(uint32_t ce32) const override {
+        U_ASSERT(!Collation::isSpecialCE32(ce32));
+        if(CollationBuilder::isTempCE32(ce32)) {
+            // retain case bits
+            return finalCEs[CollationBuilder::indexFromTempCE32(ce32)] | ((ce32 & 0xc0) << 8);
+        } else {
+            return Collation::NO_CE;
+        }
+    }
+    virtual int64_t modifyCE(int64_t ce) const override {
+        if(CollationBuilder::isTempCE(ce)) {
+            // retain case bits
+            return finalCEs[CollationBuilder::indexFromTempCE(ce)] | (ce & 0xc000);
+        } else {
+            return Collation::NO_CE;
+        }
+    }
+
+private:
+    const int64_t *finalCEs;
+};
+
+CEFinalizer::~CEFinalizer() {}
+
+void
+CollationBuilder::finalizeCEs(UErrorCode &errorCode) {
+    if(U_FAILURE(errorCode)) { return; }
+    LocalPointer<CollationDataBuilder> newBuilder(new CollationDataBuilder(icu4xMode, errorCode), errorCode);
+    if(U_FAILURE(errorCode)) {
+        return;
+    }
+    newBuilder->initForTailoring(baseData, errorCode);
+    CEFinalizer finalizer(nodes.getBuffer());
+    newBuilder->copyFrom(*dataBuilder, finalizer, errorCode);
+    if(U_FAILURE(errorCode)) { return; }
+    delete dataBuilder;
+    dataBuilder = newBuilder.orphan();
+}
+
+int32_t
+CollationBuilder::ceStrength(int64_t ce) {
+    return
+        isTempCE(ce) ? strengthFromTempCE(ce) :
+        (ce & INT64_C(0xff00000000000000)) != 0 ? UCOL_PRIMARY :
+        ((uint32_t)ce & 0xff000000) != 0 ? UCOL_SECONDARY :
+        ce != 0 ? UCOL_TERTIARY :
+        UCOL_IDENTICAL;
+}
+
+U_NAMESPACE_END
+
+U_NAMESPACE_USE
+
+U_CAPI UCollator * U_EXPORT2
+ucol_openRules(const char16_t *rules, int32_t rulesLength,
+               UColAttributeValue normalizationMode, UCollationStrength strength,
+               UParseError *parseError, UErrorCode *pErrorCode) {
+    if(U_FAILURE(*pErrorCode)) { return nullptr; }
+    if(rules == nullptr && rulesLength != 0) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+    RuleBasedCollator *coll = new RuleBasedCollator();
+    if(coll == nullptr) {
+        *pErrorCode = U_MEMORY_ALLOCATION_ERROR;
+        return nullptr;
+    }
+    UnicodeString r((UBool)(rulesLength < 0), rules, rulesLength);
+    coll->internalBuildTailoring(r, strength, normalizationMode, parseError, nullptr, *pErrorCode);
+    if(U_FAILURE(*pErrorCode)) {
+        delete coll;
+        return nullptr;
+    }
+    return coll->toUCollator();
+}
+
+static const int32_t internalBufferSize = 512;
+
+// The @internal ucol_getUnsafeSet() was moved here from ucol_sit.cpp
+// because it calls UnicodeSet "builder" code that depends on all Unicode properties,
+// and the rest of the collation "runtime" code only depends on normalization.
+// This function is not related to the collation builder,
+// but it did not seem worth moving it into its own .cpp file,
+// nor rewriting it to use lower-level UnicodeSet and Normalizer2Impl methods.
+U_CAPI int32_t U_EXPORT2
+ucol_getUnsafeSet( const UCollator *coll,
+                  USet *unsafe,
+                  UErrorCode *status)
+{
+    char16_t buffer[internalBufferSize];
+    int32_t len = 0;
+
+    uset_clear(unsafe);
+
+    // cccpattern = "[[:^tccc=0:][:^lccc=0:]]", unfortunately variant
+    static const char16_t cccpattern[25] = { 0x5b, 0x5b, 0x3a, 0x5e, 0x74, 0x63, 0x63, 0x63, 0x3d, 0x30, 0x3a, 0x5d,
+                                    0x5b, 0x3a, 0x5e, 0x6c, 0x63, 0x63, 0x63, 0x3d, 0x30, 0x3a, 0x5d, 0x5d, 0x00 };
+
+    // add chars that fail the fcd check
+    uset_applyPattern(unsafe, cccpattern, 24, USET_IGNORE_SPACE, status);
+
+    // add lead/trail surrogates
+    // (trail surrogates should need to be unsafe only if the caller tests for UTF-16 code *units*,
+    // not when testing code *points*)
+    uset_addRange(unsafe, 0xd800, 0xdfff);
+
+    USet *contractions = uset_open(0,0);
+
+    int32_t i = 0, j = 0;
+    ucol_getContractionsAndExpansions(coll, contractions, nullptr, false, status);
+    int32_t contsSize = uset_size(contractions);
+    UChar32 c = 0;
+    // Contraction set consists only of strings
+    // to get unsafe code points, we need to
+    // break the strings apart and add them to the unsafe set
+    for(i = 0; i < contsSize; i++) {
+        len = uset_getItem(contractions, i, nullptr, nullptr, buffer, internalBufferSize, status);
+        if(len > 0) {
+            j = 0;
+            while(j < len) {
+                U16_NEXT(buffer, j, len, c);
+                if(j < len) {
+                    uset_add(unsafe, c);
+                }
+            }
+        }
+    }
+
+    uset_close(contractions);
+
+    return uset_size(unsafe);
+}
+
+#endif  // !UCONFIG_NO_COLLATION