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diff --git a/include/rtl/stringconcat.hxx b/include/rtl/stringconcat.hxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef RTL_STRINGCONCAT_HXX
+#define RTL_STRINGCONCAT_HXX
+
+#include <rtl/stringutils.hxx>
+
+#include <string.h>
+
+#ifdef RTL_FAST_STRING
+
+#ifdef RTL_STRING_UNITTEST
+#define rtl rtlunittest
+#endif
+namespace rtl
+{
+#ifdef RTL_STRING_UNITTEST
+#undef rtl
+#endif
+
+/*
+Implementation of efficient string concatenation.
+
+The whole system is built around two basic template classes:
+- ToStringHelper< T > - for each T it can give the length of the resulting string representation and can write
+    this string representation to a buffer
+- O(U)StringConcat< T1, T2 > - operator+ now, instead of creating O(U)String object, returns only this helper object,
+    that keeps a reference to both operator+ operands; only when converted to O(U)String it will actually create
+    the resulting string object using ToStringHelper, creating directly the resulting object without any string
+    intermediate objects
+As all the code is inline methods, it allows for extensive optimization and will usually result in very effective code
+(even surpassing strlen/strcat and equalling handwritten), while allowing for very easy and intuitive syntax.
+*/
+
+/**
+@internal
+
+Helper class for converting a given type to a string representation.
+*/
+template< typename T >
+struct ToStringHelper
+    {
+    /// Return length of the string representation of the given object (if not known exactly, it needs to be the maximum).
+    static int length( const T& );
+    /// Add 8-bit representation of the given object to the given buffer and return position right after the added data.
+    static char* addData( char* buffer, const T& );
+    /// Add Unicode representation of the given object to the given buffer and return position right after the added data.
+    static sal_Unicode* addData( sal_Unicode* buffer, const T& );
+    /// If true, T can be used in concatenation resulting in OString.
+    static const bool allowOStringConcat = false;
+    /// If true, T can be used in concatenation resulting in OUString.
+    static const bool allowOUStringConcat = false;
+    };
+
+inline
+char* addDataHelper( char* buffer, const char* data, int length )
+    {
+    memcpy( buffer, data, length );
+    return buffer + length;
+    }
+
+inline
+sal_Unicode* addDataHelper( sal_Unicode* buffer, const sal_Unicode* data, int length )
+    {
+    memcpy( buffer, data, length * sizeof( sal_Unicode ));
+    return buffer + length;
+    }
+
+inline
+sal_Unicode* addDataLiteral( sal_Unicode* buffer, const char* data, int length )
+    {
+    while( length-- > 0 )
+        *buffer++ = *data++;
+    return buffer;
+    }
+
+inline
+char* addDataCString( char* buffer, const char* str )
+    {
+    while( *str != '\0' )
+        *buffer++ = *str++;
+    return buffer;
+    }
+
+inline
+sal_Unicode* addDataUString( sal_Unicode* buffer, const sal_Unicode* str )
+    {
+    while( *str != '\0' )
+        *buffer++ = *str++;
+    return buffer;
+    }
+
+template<>
+struct ToStringHelper< const char* >
+    {
+    static int length( const char* str ) {
+        return sal::static_int_cast<int>(strlen( str ));
+    }
+    static char* addData( char* buffer, const char* str ) { return addDataCString( buffer, str ); }
+    static const bool allowOStringConcat = true;
+    static const bool allowOUStringConcat = false;
+    };
+
+template<>
+struct ToStringHelper< char* >
+    {
+    static int length( const char* str ) {
+        return sal::static_int_cast<int>(strlen( str ));
+    }
+    static char* addData( char* buffer, const char* str ) { return addDataCString( buffer, str ); }
+    static const bool allowOStringConcat = true;
+    static const bool allowOUStringConcat = false;
+    };
+
+template< int N >
+struct ToStringHelper< char[ N ] >
+    {
+    static int length( const char str[ N ] ) {
+        return sal::static_int_cast<int>(strlen( str ));
+    }
+    static char* addData( char* buffer, const char str[ N ] ) { return addDataCString( buffer, str ); }
+    static sal_Unicode* addData( sal_Unicode* buffer, const char str[ N ] ) { return addDataLiteral( buffer, str, N - 1 ); }
+    static const bool allowOStringConcat = true;
+    static const bool allowOUStringConcat = false;
+    };
+
+template< int N >
+struct ToStringHelper< const char[ N ] >
+    {
+    static int length( const char str[ N ] ) { (void)str; assert( strlen( str ) == N - 1 ); return N - 1; }
+    static char* addData( char* buffer, const char str[ N ] ) { return addDataHelper( buffer, str, N - 1 ); }
+    static sal_Unicode* addData( sal_Unicode* buffer, const char str[ N ] ) { return addDataLiteral( buffer, str, N - 1 ); }
+    static const bool allowOStringConcat = true;
+    static const bool allowOUStringConcat = true;
+    };
+
+/**
+@internal
+
+Objects returned by operator+, instead of OString. These objects (possibly recursively) keep a representation of the whole
+concatenation operation.
+*/
+template< typename T1, typename T2 >
+struct OStringConcat
+    {
+    public:
+        OStringConcat( const T1& left_, const T2& right_ ) : left( left_ ), right( right_ ) {}
+        int length() const { return ToStringHelper< T1 >::length( left ) + ToStringHelper< T2 >::length( right ); }
+        char* addData( char* buffer ) const { return ToStringHelper< T2 >::addData( ToStringHelper< T1 >::addData( buffer, left ), right ); }
+        // NOTE here could be functions that would forward to the "real" temporary OString. Note however that e.g. getStr()
+        // is not so simple, as the OString temporary must live long enough (i.e. can't be created here in a function, a wrapper
+        // temporary object containing it must be returned instead).
+    private:
+        const T1& left;
+        const T2& right;
+    };
+
+/**
+@internal
+
+Objects returned by operator+, instead of OUString. These objects (possibly recursively) keep a representation of the whole
+concatenation operation.
+*/
+template< typename T1, typename T2 >
+struct OUStringConcat
+    {
+    public:
+        OUStringConcat( const T1& left_, const T2& right_ ) : left( left_ ), right( right_ ) {}
+        int length() const { return ToStringHelper< T1 >::length( left ) + ToStringHelper< T2 >::length( right ); }
+        sal_Unicode* addData( sal_Unicode* buffer ) const { return ToStringHelper< T2 >::addData( ToStringHelper< T1 >::addData( buffer, left ), right ); }
+    private:
+        const T1& left;
+        const T2& right;
+    };
+
+template< typename T1, typename T2 >
+struct ToStringHelper< OStringConcat< T1, T2 > >
+    {
+    static int length( const OStringConcat< T1, T2 >& c ) { return c.length(); }
+    static char* addData( char* buffer, const OStringConcat< T1, T2 >& c ) { return c.addData( buffer ); }
+    static const bool allowOStringConcat = ToStringHelper< T1 >::allowOStringConcat && ToStringHelper< T2 >::allowOStringConcat;
+    static const bool allowOUStringConcat = false;
+    };
+
+template< typename T1, typename T2 >
+struct ToStringHelper< OUStringConcat< T1, T2 > >
+    {
+    static int length( const OUStringConcat< T1, T2 >& c ) { return c.length(); }
+    static sal_Unicode* addData( sal_Unicode* buffer, const OUStringConcat< T1, T2 >& c ) { return c.addData( buffer ); }
+    static const bool allowOStringConcat = false;
+    static const bool allowOUStringConcat = ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat;
+    };
+
+template< typename T1, typename T2 >
+inline
+SAL_WARN_UNUSED_RESULT
+typename internal::Enable< OStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOStringConcat && ToStringHelper< T2 >::allowOStringConcat >::Type operator+( const T1& left, const T2& right )
+    {
+    return OStringConcat< T1, T2 >( left, right );
+    }
+
+// char[N] and const char[N] need to be done explicitly, otherwise the compiler likes to treat them the same way for some reason
+template< typename T, int N >
+inline
+SAL_WARN_UNUSED_RESULT
+typename internal::Enable< OStringConcat< T, const char[ N ] >, ToStringHelper< T >::allowOStringConcat >::Type operator+( const T& left, const char (&right)[ N ] )
+    {
+    return OStringConcat< T, const char[ N ] >( left, right );
+    }
+
+template< typename T, int N >
+inline
+SAL_WARN_UNUSED_RESULT
+typename internal::Enable< OStringConcat< const char[ N ], T >, ToStringHelper< T >::allowOStringConcat >::Type operator+( const char (&left)[ N ], const T& right )
+    {
+    return OStringConcat< const char[ N ], T >( left, right );
+    }
+
+template< typename T, int N >
+inline
+SAL_WARN_UNUSED_RESULT
+typename internal::Enable< OStringConcat< T, char[ N ] >, ToStringHelper< T >::allowOStringConcat >::Type operator+( const T& left, char (&right)[ N ] )
+    {
+    return OStringConcat< T, char[ N ] >( left, right );
+    }
+
+template< typename T, int N >
+inline
+SAL_WARN_UNUSED_RESULT
+typename internal::Enable< OStringConcat< char[ N ], T >, ToStringHelper< T >::allowOStringConcat >::Type operator+( char (&left)[ N ], const T& right )
+    {
+    return OStringConcat< char[ N ], T >( left, right );
+    }
+
+template< typename T1, typename T2 >
+inline
+typename internal::Enable< OUStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat >::Type operator+( const T1& left, const T2& right )
+    {
+    return OUStringConcat< T1, T2 >( left, right );
+    }
+
+template< typename T1, typename T2 >
+inline
+typename internal::Enable< OUStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat && internal::ConstCharArrayDetector< T1, void >::ok >::Type operator+( T1& left, const T2& right )
+    {
+    return OUStringConcat< T1, T2 >( left, right );
+    }
+
+template< typename T1, typename T2 >
+inline
+typename internal::Enable< OUStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat && internal::ConstCharArrayDetector< T2, void >::ok >::Type operator+( const T1& left, T2& right )
+    {
+    return OUStringConcat< T1, T2 >( left, right );
+    }
+
+#ifdef RTL_STRING_UNITTEST_CONCAT
+// Special overload to catch the remaining invalid combinations. The helper struct must
+// be used to make this operator+ overload a worse choice than all the existing overloads above.
+struct StringConcatInvalid
+    {
+    template< typename T >
+    StringConcatInvalid( const T& ) {}
+    };
+template< typename T >
+inline
+int operator+( const StringConcatInvalid&, const T& )
+    {
+    rtl_string_unittest_invalid_concat = true;
+    return 0; // doesn't matter
+    }
+#endif
+
+} // namespace
+
+#endif
+
+#endif