add taia_half

CHANGES

@@ -8,6 +8,7 @@
     This is just to get gatling to work, I may remove it again after
     that.
   implement Nikola's idea to remove limit number of strings in errmsg
+  add taia_half
 
 0.24:
   fix scan_to_sa (Tim Lorenz)

taia/taia_half.c

@@ -0,0 +1,11 @@
+#include "taia.h"
+
+/* XXX: breaks tai encapsulation */
+
+void taia_half(tai6464* t,const tai6464* u) {
+  t->atto = u->atto >> 1;
+  if (u->nano & 1) t->atto += 500000000UL;
+  t->nano = u->nano >> 1;
+  if (u->sec.x & 1) t->nano += 500000000UL;
+  t->sec.x = u->sec.x >> 1;
+}