optimisation of ltt_time_from_uint64

[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 ec4d134baf97d051ae2d3d7b87c29f837a5943b4..7cb7c8bb95914f303fd484eb7af5e8ff7ce75d07 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;
@@ -29,6 +29,7 @@ typedef struct _LttTime {
 
 
 #define NANOSECONDS_PER_SECOND 1000000000
+#define SHIFT_CONST 1.07374182400631629848
 
 static const LttTime ltt_time_zero = { 0, 0 };
 
@@ -41,7 +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;
   }
@@ -54,21 +59,27 @@ 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;
 }
 
-
+/* Fastest comparison : t1 > t2 */
 static inline int ltt_time_compare(LttTime t1, LttTime t2)
 {
-  if(t1.tv_sec > t2.tv_sec) return 1;
-  if(t1.tv_sec < t2.tv_sec) return -1;
-  if(t1.tv_nsec > t2.tv_nsec) return 1;
-  if(t1.tv_nsec < t2.tv_nsec) return -1;
-  return 0;
+  int ret=0;
+  if(likely(t1.tv_sec > t2.tv_sec)) ret = 1;
+  else if(unlikely(t1.tv_sec < t2.tv_sec)) ret = -1;
+  else if(likely(t1.tv_nsec > t2.tv_nsec)) ret = 1;
+  else if(unlikely(t1.tv_nsec < t2.tv_nsec)) ret = -1;
+  
+  return ret;
 }
 
 #define LTT_TIME_MIN(a,b) ((ltt_time_compare((a),(b)) < 0) ? (a) : (b))
@@ -85,10 +96,12 @@ static inline double ltt_time_to_double(LttTime t1)
    *
    * So we have 53-30 = 23 bits left for tv_sec.
    * */
+#ifdef EXTRA_CHECK
   g_assert(t1.tv_sec <= MAX_TV_SEC_TO_DOUBLE);
   if(t1.tv_sec > MAX_TV_SEC_TO_DOUBLE)
     g_warning("Precision loss in conversion LttTime to double");
-  return (double)t1.tv_sec + (double)t1.tv_nsec / NANOSECONDS_PER_SECOND;
+#endif //EXTRA_CHECK
+  return ((double)t1.tv_sec * (double)NANOSECONDS_PER_SECOND) + (double)t1.tv_nsec;
 }
 
 
@@ -102,12 +115,15 @@ static inline LttTime ltt_time_from_double(double t1)
    *
    * So we have 53-30 = 23 bits left for tv_sec.
    * */
+#ifdef EXTRA_CHECK
   g_assert(t1 <= MAX_TV_SEC_TO_DOUBLE);
   if(t1 > MAX_TV_SEC_TO_DOUBLE)
     g_warning("Conversion from non precise double to LttTime");
+#endif //EXTRA_CHECK
   LttTime res;
-  res.tv_sec = t1;
-  res.tv_nsec = (t1 - res.tv_sec) * NANOSECONDS_PER_SECOND;
+  //res.tv_sec = t1/(double)NANOSECONDS_PER_SECOND;
+  res.tv_sec = (guint64)(t1 * SHIFT_CONST) >> 30;
+  res.tv_nsec = (t1 - (res.tv_sec*NANOSECONDS_PER_SECOND));
   return res;
 }
 
@@ -188,12 +204,19 @@ static inline LttTime ltt_time_from_uint64(guint64 t1)
 {
   /* We lose precision if tv_sec is > than (2^62)-1
    * */
+#ifdef EXTRA_CHECK
   g_assert(t1 <= MAX_TV_SEC_TO_UINT64);
   if(t1 > MAX_TV_SEC_TO_UINT64)
-    g_warning("Conversion from non precise uint64 to LttTime");
+    g_warning("Conversion from uint64 to non precise LttTime");
+#endif //EXTRA_CHECK
   LttTime res;
-  res.tv_sec = t1/NANOSECONDS_PER_SECOND;
-  res.tv_nsec = (t1 - res.tv_sec*NANOSECONDS_PER_SECOND);
+  if(unlikely(t1 >= NANOSECONDS_PER_SECOND)) {
+    res.tv_sec = t1/NANOSECONDS_PER_SECOND;
+    res.tv_nsec = (t1 - res.tv_sec*NANOSECONDS_PER_SECOND);
+  } else {
+    res.tv_sec = 0;
+    res.tv_nsec = (guint32)t1;
+  }
   return res;
 }