bug #54712, r=rjc, a=waterson. Added a |Distance| function to calculate the span between two iterators, then added a constructor and appropriate global function to allow |Substring|s to be made from iterators in addition to the old scheme of {index,length}

git-svn-id: svn://10.0.0.236/trunk@80396 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/string/src/nsReadableUtils.cpp

@@ -27,6 +27,45 @@
 #include "nsCRT.h"
 
 
+template <class CharT> class CalculateLength
+  {
+    public:
+      typedef CharT value_type;
+
+      CalculateLength() : mDistance(0) { }
+      size_t GetDistance() const       { return mDistance; }
+
+      PRUint32 write( const CharT*, PRUint32 N )
+                                       { mDistance += N; return N; }
+    private:
+      size_t mDistance;
+  };
+
+template <class CharT>
+inline
+size_t
+Distance_Impl( const nsReadingIterator<CharT>& aStart,
+          const nsReadingIterator<CharT>& aEnd )
+  {
+    CalculateLength<CharT> sink;
+    nsReadingIterator<CharT> fromBegin(aStart);
+    copy_string(fromBegin, aEnd, sink);
+    return sink.GetDistance();
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<PRUnichar>& aStart, const nsReadingIterator<PRUnichar>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }
+
+NS_COM
+size_t
+Distance( const nsReadingIterator<char>& aStart, const nsReadingIterator<char>& aEnd )
+  {
+    return Distance_Impl(aStart, aEnd);
+  }