[src/trunk]: src/sys/sys The inline functions {ms, us, ns}2bintime() are curren...

[pgoyette <pgoyette%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/026ec981c003
branches:  trunk
changeset: 350141:026ec981c003
user:      pgoyette <pgoyette%NetBSD.org@localhost>
date:      Thu Jan 05 22:51:15 2017 +0000

description:
The inline functions {ms,us,ns}2bintime() are currently defined\nincorrectly, and always result in the bt.frac being set to zero.\nEven correcting for left- vs right shifts, the results are 
low\nprecision with at most 32 significant bits.\n\nRewrite using 64-bit multiply rather than division to get proper\nresults.  Also the multiply is less costly than a divide on most\nplatforms.

diffstat:

 sys/sys/time.h |  18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diffs (67 lines):

diff -r ec41d4cf4063 -r 026ec981c003 sys/sys/time.h
--- a/sys/sys/time.h    Thu Jan 05 21:42:04 2017 +0000
+++ b/sys/sys/time.h    Thu Jan 05 22:51:15 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: time.h,v 1.74 2016/12/18 17:18:01 christos Exp $       */
+/*     $NetBSD: time.h,v 1.75 2017/01/05 22:51:15 pgoyette Exp $       */
 
 /*
  * Copyright (c) 1982, 1986, 1993
@@ -158,6 +158,14 @@
  *   time_second ticks after N.999999999 not after N.4999999999
  */
 
+/*
+ * The magic numbers for converting to fraction:
+ *
+ *     1 ms = int(2^64 / 1000)       =  18446744073709551
+ *     1 us = int(2^64 / 1000000)    =     18446744073709
+ *     1 ns = int(2^64 / 1000000000) =        18446744073
+ */
+
 static __inline void
 bintime2timespec(const struct bintime *bt, struct timespec *ts)
 {
@@ -172,7 +180,6 @@
 {
 
        bt->sec = ts->tv_sec;
-       /* 18446744073 = int(2^64 / 1000000000) */
        bt->frac = (uint64_t)ts->tv_nsec * (uint64_t)18446744073ULL;
 }
 
@@ -190,7 +197,6 @@
 {
 
        bt->sec = tv->tv_sec;
-       /* 18446744073709 = int(2^64 / 1000000) */
        bt->frac = (uint64_t)tv->tv_usec * (uint64_t)18446744073709ULL;
 }
 
@@ -200,7 +206,7 @@
        struct bintime bt;
 
        bt.sec = (time_t)(ms / 1000U);
-       bt.frac = (((ms % 1000U) >> 32)/1000U) >> 32;
+       bt.frac = (uint64_t)(ms % 1000U) * (uint64_t)18446744073709551ULL;
 
        return bt;
 }
@@ -211,7 +217,7 @@
        struct bintime bt;
 
        bt.sec = (time_t)(us / 1000000U);
-       bt.frac = (((us % 1000000U) >> 32)/1000000U) >> 32;
+       bt.frac = (uint64_t)(us % 1000000U) * (uint64_t)18446744073709ULL;
 
        return bt;
 }
@@ -222,7 +228,7 @@
        struct bintime bt;
 
        bt.sec = (time_t)(ns / 1000000000U);
-       bt.frac = (((ns % 1000000000U) >> 32)/1000000000U) >> 32;
+       bt.frac = (uint64_t)(ns % 1000000000U) * (uint64_t)18446744073ULL;
 
        return bt;
 }