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+// © 2019 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html#License
+
+// locdistance.h
+// created: 2019may08 Markus W. Scherer
+
+#ifndef __LOCDISTANCE_H__
+#define __LOCDISTANCE_H__
+
+#include "unicode/utypes.h"
+#include "unicode/bytestrie.h"
+#include "unicode/localematcher.h"
+#include "unicode/locid.h"
+#include "unicode/uobject.h"
+#include "lsr.h"
+
+U_NAMESPACE_BEGIN
+
+struct LocaleDistanceData;
+
+/**
+ * Offline-built data for LocaleMatcher.
+ * Mostly but not only the data for mapping locales to their maximized forms.
+ */
+class LocaleDistance final : public UMemory {
+public:
+    static const LocaleDistance *getSingleton(UErrorCode &errorCode);
+
+    /**
+     * Finds the supported LSR with the smallest distance from the desired one.
+     * Equivalent LSR subtags must be normalized into a canonical form.
+     *
+     * <p>Returns the index of the lowest-distance supported LSR in bits 31..8
+     * (negative if none has a distance below the threshold),
+     * and its distance (0..ABOVE_THRESHOLD) in bits 7..0.
+     */
+    int32_t getBestIndexAndDistance(const LSR &desired,
+                                    const LSR **supportedLSRs, int32_t supportedLSRsLength,
+                                    int32_t threshold, ULocMatchFavorSubtag favorSubtag) const;
+
+    int32_t getParadigmLSRsLength() const { return paradigmLSRsLength; }
+
+    UBool isParadigmLSR(const LSR &lsr) const;
+
+    int32_t getDefaultScriptDistance() const {
+        return defaultScriptDistance;
+    }
+
+    int32_t getDefaultDemotionPerDesiredLocale() const {
+        return defaultDemotionPerDesiredLocale;
+    }
+
+private:
+    LocaleDistance(const LocaleDistanceData &data);
+    LocaleDistance(const LocaleDistance &other) = delete;
+    LocaleDistance &operator=(const LocaleDistance &other) = delete;
+
+    static void initLocaleDistance(UErrorCode &errorCode);
+
+    static int32_t getDesSuppScriptDistance(BytesTrie &iter, uint64_t startState,
+                                            const char *desired, const char *supported);
+
+    static int32_t getRegionPartitionsDistance(
+        BytesTrie &iter, uint64_t startState,
+        const char *desiredPartitions, const char *supportedPartitions,
+        int32_t threshold);
+
+    static int32_t getFallbackRegionDistance(BytesTrie &iter, uint64_t startState);
+
+    static int32_t trieNext(BytesTrie &iter, const char *s, bool wantValue);
+
+    const char *partitionsForRegion(const LSR &lsr) const {
+        // ill-formed region -> one non-matching string
+        int32_t pIndex = regionToPartitionsIndex[lsr.regionIndex];
+        return partitionArrays[pIndex];
+    }
+
+    int32_t getDefaultRegionDistance() const {
+        return defaultRegionDistance;
+    }
+
+    // The trie maps each dlang+slang+dscript+sscript+dregion+sregion
+    // (encoded in ASCII with bit 7 set on the last character of each subtag) to a distance.
+    // There is also a trie value for each subsequence of whole subtags.
+    // One '*' is used for a (desired, supported) pair of "und", "Zzzz"/"", or "ZZ"/"".
+    BytesTrie trie;
+
+    /**
+     * Maps each region to zero or more single-character partitions.
+     */
+    const uint8_t *regionToPartitionsIndex;
+    const char **partitionArrays;
+
+    /**
+     * Used to get the paradigm region for a cluster, if there is one.
+     */
+    const LSR *paradigmLSRs;
+    int32_t paradigmLSRsLength;
+
+    int32_t defaultLanguageDistance;
+    int32_t defaultScriptDistance;
+    int32_t defaultRegionDistance;
+    int32_t minRegionDistance;
+    int32_t defaultDemotionPerDesiredLocale;
+};
+
+U_NAMESPACE_END
+
+#endif  // __LOCDISTANCE_H__