#1058. Change comparator to return -1 : 0 : 1

include/exiv2/value.hpp

@@ -872,21 +872,29 @@ namespace Exiv2 {
     }; // class XmpArrayValue
 
     /*!
-      @brief %LangAltValueComparison
+      @brief %LangAltValueComparator
 
       #1058
 	  https://www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMPSpecificationPart1.pdf
 	  XMP spec chapter B.4 (page 42) the xml:lang qualifier is to be compared case insensitive.
       */
 	struct LangAltValueComparator {
-		bool operator() (const std::string& str1, const std::string& str2) const
+		int operator() (const std::string& str1, const std::string& str2) const
 		{
-    		bool result = str1.size() != str2.size();
-    		for (std::string::const_iterator c1 = str1.begin()
-    		                               , c2 = str2.begin()
-    		    ; result && c1 != str1.end()
-    		    ; ++c1, ++c2) {
-        			result = tolower(*c1) != tolower(*c2);
+    		int result = str1.size() < str2.size() ? -1
+    		           : str1.size() > str2.size() ?  1
+    		           : 0
+    		           ;
+    		std::string::const_iterator c1 = str1.begin();
+    		std::string::const_iterator c2 = str2.begin();
+    		for (
+    		    ; result==0 && c1 != str1.end()
+    		    ; ++c1, ++c2
+    		    ) {
+        		result = tolower(*c1) < tolower(*c2) ? -1
+        		       : tolower(*c1) > tolower(*c2) ?  1
+        		       : 0
+        		       ;
     		}
     		return result;
     	}