Add alternate timestamp implementations

Add mach_absolute_time and gettimeofday timestamp implementations, and
fix clock_gettime check so that it can actually succeed

src/network/network.cc

@@ -16,6 +16,8 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include "config.h"
+
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
@@ -23,6 +25,14 @@
 #include <assert.h>
 #include <errno.h>
 
+#if HAVE_CLOCK_GETTIME
+ #include <time.h>
+#elif HAVE_MACH_ABSOLUTE_TIME
+ #include <mach/mach_time.h>
+#elif HAVE_GETTIMEOFDAY
+ #include <sys/time.h>
+#endif
+
 #include "dos_assert.h"
 #include "byteorder.h"
 #include "network.h"
@@ -282,6 +292,7 @@ int Connection::port( void ) const
 
 uint64_t Network::timestamp( void )
 {
+#if HAVE_CLOCK_GETTIME
   struct timespec tp;
 
   if ( clock_gettime( CLOCK_MONOTONIC, &tp ) < 0 ) {
@@ -292,6 +303,30 @@ uint64_t Network::timestamp( void )
   millis += uint64_t( tp.tv_sec ) * 1000;
 
   return millis;
+#elif HAVE_MACH_ABSOLUTE_TIME
+  static mach_timebase_info_data_t s_timebase_info;
+
+  if (s_timebase_info.denom == 0) {
+    mach_timebase_info(&s_timebase_info);
+  }
+
+  // NB: mach_absolute_time() returns "absolute time units"
+  // We need to apply a conversion to get milliseconds.
+  return ((mach_absolute_time() * s_timebase_info.numer) / (1000000 * s_timebase_info.denom));
+#elif HAVE_GETTIMEOFDAY
+  // NOTE: If time steps backwards, timeouts may be confused.
+  struct timeval tv;
+  if ( gettimeofday(&tv, NULL) ) {
+    throw NetworkException( "gettimeofday", errno );
+  }
+
+  uint64_t millis = tv.tv_usec / 1000;
+  millis += uint64_t( tv.tv_sec ) * 1000;
+
+  return millis;
+#else
+# error "Don't know how to get a timestamp on this platform"
+#endif
 }
 
 uint16_t Network::timestamp16( void )