From ea2c000633765fbfb42e63a74b8ee3fb10bb4aff Mon Sep 17 00:00:00 2001
From: Xin LI <delphij@FreeBSD.org>
Date: Fri, 12 Mar 2010 00:51:13 +0000
Subject: [PATCH] MFC r203760: Improve time precision for grdc(6):

Traditionally, grdc would obtain time through time(3) which in turn gets
only the second part of clock (CLOCK_SECOND), and sleep for 1 second after
each screen refresh.

This approach would have two problems.  First, we are not guaranteed to
be waken up at the beginning of a whole second, which will typically
exhibit as a "lag" on second number.  Second, because we sleep for whole
second, and the refresh process would take some time, the error would
accumulate from time to time, making the lag variable.

Make grdc(6) to use time(3) to get time only at the beginning, and sample
time in CLOCK_REALTIME_FAST granularity after refreshing, and use the
nanosecond part to caculate how much time we want to sleep.

PR:		bin/120813
---
 games/grdc/grdc.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/games/grdc/grdc.c b/games/grdc/grdc.c
index d27b10ed791..c467b533e28 100644
--- a/games/grdc/grdc.c
+++ b/games/grdc/grdc.c
@@ -59,6 +59,7 @@ main(argc, argv)
 int argc;
 char **argv;
 {
+struct timespec ts;
 long t, a;
 int i, j, s, k;
 int n;
@@ -136,9 +137,9 @@ int t12;
 
 		attrset(COLOR_PAIR(2));
 	}
+	time(&now);
 	do {
 		mask = 0;
-		time(&now);
 		tm = localtime(&now);
 		set(tm->tm_sec%10, 0);
 		set(tm->tm_sec/10, 4);
@@ -193,7 +194,19 @@ int t12;
 		}
 		movto(6, 0);
 		refresh();
-		sleep(1);
+		clock_gettime(CLOCK_REALTIME_FAST, &ts);
+		if (ts.tv_sec == now) {
+			if (ts.tv_nsec > 0) {
+				ts.tv_sec = 0;
+				ts.tv_nsec = 1000000000 - ts.tv_nsec;
+			} else {
+				ts.tv_sec = 1;
+				ts.tv_nsec = 0;
+			}
+			nanosleep(&ts, NULL);
+			now = ts.tv_sec + 1;
+		} else
+			now = ts.tv_sec;
 		if (sigtermed) {
 			standend();
 			clear();