likely/unlikely branch prediction

[lttv.git] / ltt / branches / poly / ltt / time.h

diff --git a/ltt/branches/poly/ltt/time.h b/ltt/branches/poly/ltt/time.h
index a257018275262b2dd2da7b87a5fc1e1598492a02..fe7641dfbbf49fdcc871e37ac3d55e1994a36b40 100644 (file)
--- a/ltt/branches/poly/ltt/time.h
+++ b/ltt/branches/poly/ltt/time.h
@@ -20,7 +20,7 @@
 #define LTT_TIME_H
 
 #include <glib.h>
-
+#include <ltt/compiler.h>
 
 typedef struct _LttTime {
   unsigned long tv_sec;
@@ -42,7 +42,11 @@ static inline LttTime ltt_time_sub(LttTime t1, LttTime t2)
   LttTime res;
   res.tv_sec  = t1.tv_sec  - t2.tv_sec;
   res.tv_nsec = t1.tv_nsec - t2.tv_nsec;
-  if(t1.tv_nsec < t2.tv_nsec) {
+  /* unlikely : given equal chance to be anywhere in t1.tv_nsec, and
+   * higher probability of low value for t2.tv_sec, we will habitually
+   * not wrap.
+   */
+  if(unlikely(t1.tv_nsec < t2.tv_nsec)) {
     res.tv_sec--;
     res.tv_nsec += NANOSECONDS_PER_SECOND;
   }
@@ -55,16 +59,17 @@ static inline LttTime ltt_time_add(LttTime t1, LttTime t2)
   LttTime res;
   res.tv_nsec = t1.tv_nsec + t2.tv_nsec;
   res.tv_sec = t1.tv_sec + t2.tv_sec;
-  if(res.tv_nsec >= NANOSECONDS_PER_SECOND) {
+  /* unlikely : given equal chance to be anywhere in t1.tv_nsec, and
+   * higher probability of low value for t2.tv_sec, we will habitually
+   * not wrap.
+   */
+  if(unlikely(res.tv_nsec >= NANOSECONDS_PER_SECOND)) {
     res.tv_sec++;
     res.tv_nsec -= NANOSECONDS_PER_SECOND;
   }
   return res;
 }
 
-#define likely(x) __builtin_expect(!!(x), 1)
-#define unlikely(x) __builtin_expect(!!(x), 0)
-
 /* Fastest comparison : t1 > t2 */
 static inline int ltt_time_compare(LttTime t1, LttTime t2)
 {