From d2c7ea6ec2133836bf1ec756a53bf504f1c19a2b Mon Sep 17 00:00:00 2001
From: letouzey
Date: Fri, 5 Oct 2012 11:22:01 +0000
Subject: More accurate timings for "Time foo"

 The elapsed time in seconds was computed via a difference of Unix.time(),
 but these Unix.time() aren't precise enough (just a number of seconds),
 and a difference is hence even less precise.  We now use Unix.gettimeofday,
 and round the time difference to the millisecond.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@15858 85f007b7-540e-0410-9357-904b9bb8a0f7
---
 lib/system.ml | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/lib/system.ml b/lib/system.ml
index 6076217b30..84706d0313 100644
--- a/lib/system.ml
+++ b/lib/system.ml
@@ -198,15 +198,18 @@ let connect writefun readfun com =
 type time = float * float * float
 
 let get_time () =
-  let t = times ()  in
-  (time(), t.tms_utime, t.tms_stime)
+  let t = Unix.times ()  in
+  (Unix.gettimeofday(), t.tms_utime, t.tms_stime)
 
-let time_difference (t1,_,_) (t2,_,_) = t2 -. t1
+(* Keep only 3 significant digits *)
+let round f = (floor (f *. 1e3)) *. 1e-3
+
+let time_difference (t1,_,_) (t2,_,_) = round (t2 -. t1)
 
 let fmt_time_difference (startreal,ustart,sstart) (stopreal,ustop,sstop) =
-  real (stopreal -. startreal) ++ str " secs " ++
+  real (round (stopreal -. startreal)) ++ str " secs " ++
   str "(" ++
-  real ((-.) ustop ustart) ++ str "u" ++
+  real (round (ustop -. ustart)) ++ str "u" ++
   str "," ++
-  real ((-.) sstop sstart) ++ str "s" ++
+  real (round (sstop -. sstart)) ++ str "s" ++
   str ")"
-- 
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