Fix computation of length of LTL formulas.

* src/ltlvisit/length.cc: Fix computation for ltl::multop
operator. "a&b&c" was reported with length 3, ignoring the
"&" operators, because of a typo.
* src/ltlvisit/length.hh: Fix description to correctly
reflect this change intended since 2010-01-22.
* src/ltltest/length.test, src/ltltest/length.cc: New files.
* src/ltltest/Makefile.am: Add them.

src/ltlvisit/length.cc

@@ -53,7 +53,7 @@ namespace spot
 	    mo->nth(i)->accept(*this);
 	  // "a & b & c" should count for 5, even though it is
 	  // stored as And(a,b,c).
-	  mo += s - 1;
+	  result_ += s - 1;
 	}
 
 	virtual void

src/ltlvisit/length.hh

@@ -1,3 +1,5 @@
+// Copyright (C) 2012 Laboratoire de Recherche et Developement de
+// l'Epita (LRDE).
 // Copyright (C) 2004, 2005  Laboratoire d'Informatique de Paris 6 (LIP6),
 // département Systèmes Répartis Coopératifs (SRC), Université Pierre
 // et Marie Curie.
@@ -33,10 +35,10 @@ namespace spot
     ///
     /// The length of a formula is the number of atomic properties,
     /// constants, and operators (logical and temporal) occurring in
-    /// the formula.  spot::ltl::multops count only for 1, even if
-    /// they have more than two operands (e.g. <code>a | b | c</code>
-    /// has length 4, because <code>|</code> is represented once
-    /// internally).
+    /// the formula.  spot::ltl::multop instances with n arguments
+    /// count only n-1; for instance <code>a | b | c</code>
+    /// has length 5, even if there is only as single <code>|</code> node
+    /// internally.
     int length(const formula* f);
   }
 }