1 files changed, 98 insertions, 0 deletions
diff --git a/thirdparty/icu4c/common/uniquecharstr.h b/thirdparty/icu4c/common/uniquecharstr.h
new file mode 100644
index 0000000000..10cc924f7f
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+++ b/thirdparty/icu4c/common/uniquecharstr.h
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+// © 2020 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+
+// uniquecharstr.h
+// created: 2020sep01 Frank Yung-Fong Tang
+
+#ifndef __UNIQUECHARSTR_H__
+#define __UNIQUECHARSTR_H__
+
+#include "charstr.h"
+#include "uassert.h"
+#include "uhash.h"
+
+U_NAMESPACE_BEGIN
+
+/**
+ * Stores NUL-terminated strings with duplicate elimination.
+ * Checks for unique UTF-16 string pointers and converts to invariant characters.
+ *
+ * Intended to be stack-allocated. Add strings, get a unique number for each,
+ * freeze the object, get a char * pointer for each string,
+ * call orphanCharStrings() to capture the string storage, and let this object go out of scope.
+ */
+class UniqueCharStrings {
+public:
+    UniqueCharStrings(UErrorCode &errorCode) : strings(nullptr) {
+        // Note: We hash on string contents but store stable char16_t * pointers.
+        // If the strings are stored in resource bundles which should be built with
+        // duplicate elimination, then we should be able to hash on just the pointer values.
+        uhash_init(&map, uhash_hashUChars, uhash_compareUChars, uhash_compareLong, &errorCode);
+        if (U_FAILURE(errorCode)) { return; }
+        strings = new CharString();
+        if (strings == nullptr) {
+            errorCode = U_MEMORY_ALLOCATION_ERROR;
+        }
+    }
+    ~UniqueCharStrings() {
+        uhash_close(&map);
+        delete strings;
+    }
+
+    /** Returns/orphans the CharString that contains all strings. */
+    CharString *orphanCharStrings() {
+        CharString *result = strings;
+        strings = nullptr;
+        return result;
+    }
+
+    /**
+     * Adds a string and returns a unique number for it.
+     * The string's buffer contents must not change, nor move around in memory,
+     * while this UniqueCharStrings is in use.
+     * The string contents must be NUL-terminated exactly at s.length().
+     *
+     * Best used with read-only-alias UnicodeString objects that point to
+     * stable storage, such as strings returned by resource bundle functions.
+     */
+    int32_t add(const UnicodeString &s, UErrorCode &errorCode) {
+        if (U_FAILURE(errorCode)) { return 0; }
+        if (isFrozen) {
+            errorCode = U_NO_WRITE_PERMISSION;
+            return 0;
+        }
+        // The string points into the resource bundle.
+        const char16_t *p = s.getBuffer();
+        int32_t oldIndex = uhash_geti(&map, p);
+        if (oldIndex != 0) {  // found duplicate
+            return oldIndex;
+        }
+        // Explicit NUL terminator for the previous string.
+        // The strings object is also terminated with one implicit NUL.
+        strings->append(0, errorCode);
+        int32_t newIndex = strings->length();
+        strings->appendInvariantChars(s, errorCode);
+        uhash_puti(&map, const_cast<char16_t *>(p), newIndex, &errorCode);
+        return newIndex;
+    }
+
+    void freeze() { isFrozen = true; }
+
+    /**
+     * Returns a string pointer for its unique number, if this object is frozen.
+     * Otherwise nullptr.
+     */
+    const char *get(int32_t i) const {
+        U_ASSERT(isFrozen);
+        return isFrozen && i > 0 ? strings->data() + i : nullptr;
+    }
+
+private:
+    UHashtable map;
+    CharString *strings;
+    bool isFrozen = false;
+};
+
+U_NAMESPACE_END
+
+#endif  // __UNIQUECHARSTR_H__