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List:       busybox-cvs
Subject:    [git commit] ntpd: fold d_to_tv() into its only caller
From:       Denys Vlasenko <vda.linux () googlemail ! com>
Date:       2023-01-18 16:42:17
Message-ID: 20230118170547.A5A1987CEE () busybox ! osuosl ! org
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commit: https://git.busybox.net/busybox/commit/?id=479bd7af0d24d123326c1ceb447e015e9e2955d7
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
 networking/ntpd.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/networking/ntpd.c b/networking/ntpd.c
index ff49550e9..db04eb272 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -551,13 +551,6 @@ gettime1900d(void)
 	return G.cur_time;
 }
 
-static void
-d_to_tv(struct timeval *tv, double d)
-{
-	tv->tv_sec = (time_t)d;
-	tv->tv_usec = (d - tv->tv_sec) * 1000000;
-}
-
 static NOINLINE double
 lfp_to_d(l_fixedpt_t lfp)
 {
@@ -1044,8 +1037,17 @@ step_time(double offset)
 	time_t tval;
 
 	xgettimeofday(&tvc);
+	/* This code adds floating point value on the order of 1.0
+	 * to a value of ~4 billion (as of years 203x).
+	 * With 52-bit mantissa, "only" 20 bits of offset's precision
+	 * are used (0.01 attosecond), the rest is lost.
+	 * Some 200 billion years later, when tvc.tv_sec would have
+	 * 63 significant bits, the precision loss would be catastrophic,
+	 * a more complex code would be needed.
+	 */
 	dtime = tvc.tv_sec + (1.0e-6 * tvc.tv_usec) + offset;
-	d_to_tv(&tvn, dtime);
+	tvn.tv_sec = (time_t)dtime;
+	tvn.tv_usec = (dtime - tvn.tv_sec) * 1000000;
 	xsettimeofday(&tvn);
 
 	VERB2 {
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