timer: add a stopwatch for timing a simple operation

* src/misc/timer.hh (stopwatch): New class, implemented on top
of C++11's std::chrono::high_resolution_clock.
* src/bin/dstar2tgba.cc, src/bin/ltl2tgba.cc, src/bin/ltlcross.cc:
Use it in lieu of gethrxtime(), so we do not need to distribute
gethrxtime anymore.

src/bin/dstar2tgba.cc

@@ -24,7 +24,6 @@
 
 #include <argp.h>
 #include "error.h"
-#include "gethrxtime.h"
 
 #include "common_setup.hh"
 #include "common_finput.hh"
@@ -40,6 +39,7 @@
 #include "tgbaalgos/stats.hh"
 #include "tgba/bddprint.hh"
 #include "misc/optionmap.hh"
+#include "misc/timer.hh"
 #include "dstarparse/public.hh"
 #include "tgbaalgos/sccinfo.hh"
 
@@ -305,14 +305,11 @@ namespace
       if (!daut)
 	error(2, 0, "failed to read automaton from %s", filename);
 
-      const xtime_t before = gethrxtime();
-
+      spot::stopwatch sw;
+      sw.start();
       auto nba = spot::dstar_to_tgba(daut);
       auto aut = post.run(nba, 0);
-
-      const xtime_t after = gethrxtime();
-      const double prec = XTIME_PRECISION;
-      const double conversion_time = (after - before) / prec;
+      const double conversion_time = sw.stop();
 
       switch (format)
 	{

src/bin/ltl2tgba.cc

@@ -24,7 +24,6 @@
 
 #include <argp.h>
 #include "error.h"
-#include "gethrxtime.h"
 
 #include "common_setup.hh"
 #include "common_r.hh"
@@ -44,6 +43,7 @@
 #include "tgbaalgos/translate.hh"
 #include "tgba/bddprint.hh"
 #include "misc/optionmap.hh"
+#include "misc/timer.hh"
 
 const char argp_program_doc[] ="\
 Translate linear-time formulas (LTL/PSL) into Büchi automata.\n\n\
@@ -223,11 +223,10 @@ namespace
     process_formula(const spot::ltl::formula* f,
 		    const char* filename = 0, int linenum = 0)
     {
-      const xtime_t before = gethrxtime();
+      spot::stopwatch sw;
+      sw.start();
       auto aut = trans.run(&f);
-      const xtime_t after = gethrxtime();
-      const double prec = XTIME_PRECISION;
-      const double translation_time = (after - before) / prec;
+      const double translation_time = sw.stop();
 
       // This should not happen, because the parser we use can only
       // read PSL/LTL formula, but since our ltl::formula* type can

src/bin/ltlcross.cc

@@ -31,7 +31,6 @@
 #include <unistd.h>
 #include <sys/wait.h>
 #include "error.h"
-#include "gethrxtime.h"
 #include "argmatch.h"
 
 #include "common_setup.hh"
@@ -61,6 +60,7 @@
 #include "misc/hash.hh"
 #include "misc/random.hh"
 #include "misc/tmpfile.hh"
+#include "misc/timer.hh"
 
 // Disable handling of timeout on systems that miss kill() or alarm().
 // For instance MinGW.
@@ -892,9 +892,10 @@ namespace
       std::string cmd = command.str();
       std::cerr << "Running [" << l << translator_num << "]: "
 		<< cmd << std::endl;
-      xtime_t before = gethrxtime();
+      spot::stopwatch sw;
+      sw.start();
       int es = exec_with_timeout(cmd.c_str());
-      xtime_t after = gethrxtime();
+      double duration = sw.stop();
 
       const char* status_str = 0;
 
@@ -1043,8 +1044,7 @@ namespace
 	  statistics* st = &(*fstats)[translator_num];
 	  st->status_str = status_str;
 	  st->status_code = es;
-	  double prec = XTIME_PRECISION;
-	  st->time = (after - before) / prec;
+	  st->time = duration;
 
 	  // Compute statistics.
 	  if (res)

src/misc/timer.hh

@@ -29,6 +29,7 @@
 # include <iosfwd>
 # include <string>
 # include <map>
+# include <chrono>
 # if SPOT_HAVE_SYS_TIMES_H
 #  include <sys/times.h>
 # endif
@@ -40,6 +41,33 @@ namespace spot
   /// \addtogroup misc_tools
   /// @{
 
+
+  /// \brief A simple stopwatch
+  struct stopwatch
+  {
+  protected:
+    typedef std::chrono::high_resolution_clock clock;
+    clock::time_point start_;
+  public:
+    /// Marks the start if the measurement
+    void start()
+    {
+      start_ = clock::now();
+    }
+
+    /// \brief Returns the elapsed duration in seconds.
+    ///
+    /// May be called multiple times, and will always return the
+    /// duration since the last call to start().
+    double stop()
+    {
+      auto t = clock::now();
+      typedef std::chrono::duration<double> seconds;
+      return std::chrono::duration_cast<seconds>(t - start_).count();
+    }
+  };
+
+
   /// A structure to record elapsed time in clock ticks.
   struct time_info
   {