[src/trunk]: src/sys/dev Fix leap year handling for years 2100 and greater.

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

details:   https://anonhg.NetBSD.org/src/rev/9b97fbc0bb65
branches:  trunk
changeset: 347137:9b97fbc0bb65
user:      jakllsch <jakllsch%NetBSD.org@localhost>
date:      Mon Aug 15 15:51:39 2016 +0000

description:
Fix leap year handling for years 2100 and greater.

I can not explain why this works and the existing code doesn't.
Maybe it has something to do with leap years happening at the end of a
four year period and not at the beggining, and there being no year 0?

diffstat:

 sys/dev/clock_subr.c |  20 ++++++++++----------
 1 files changed, 10 insertions(+), 10 deletions(-)

diffs (60 lines):

diff -r 74b1935bce4d -r 9b97fbc0bb65 sys/dev/clock_subr.c
--- a/sys/dev/clock_subr.c      Mon Aug 15 14:45:31 2016 +0000
+++ b/sys/dev/clock_subr.c      Mon Aug 15 15:51:39 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: clock_subr.c,v 1.26 2014/12/22 18:09:20 christos Exp $ */
+/*     $NetBSD: clock_subr.c,v 1.27 2016/08/15 15:51:39 jakllsch Exp $ */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -50,7 +50,7 @@
 
 #ifdef _KERNEL
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: clock_subr.c,v 1.26 2014/12/22 18:09:20 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: clock_subr.c,v 1.27 2016/08/15 15:51:39 jakllsch Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -67,8 +67,8 @@
 #define FEBRUARY       2
 
 /* for easier alignment:
- * time from the epoch to 2000 (there were 7 leap years): */
-#define        DAYSTO2000      (365*30+7)
+ * time from the epoch to 2001 (there were 8 leap years): */
+#define        DAYSTO2001      (365*31+8)
 
 /* 4 year intervals include 1 leap year */
 #define        DAYS4YEARS      (365*4+1)
@@ -96,14 +96,14 @@
        if (is_leap_year(year) && dt->dt_mon > FEBRUARY)
                days++;
 
-       if (year < 2000) {
+       if (year < 2001) {
                /* simple way for early years */
                for (i = POSIX_BASE_YEAR; i < year; i++)
                        days += days_per_year(i);
        } else {
                /* years are properly aligned */
-               days += DAYSTO2000;
-               year -= 2000;
+               days += DAYSTO2001;
+               year -= 2001;
 
                i = year / 400;
                days += i * DAYS400YEARS;
@@ -155,9 +155,9 @@
        /* Day of week (Note: 1/1/1970 was a Thursday) */
        dt->dt_wday = (days + 4) % 7;
 
-       if (days >= DAYSTO2000) {
-               days -= DAYSTO2000;
-               dt->dt_year = 2000;
+       if (days >= DAYSTO2001) {
+               days -= DAYSTO2001;
+               dt->dt_year = 2001;
 
                i = days / DAYS400YEARS;
                days -= i*DAYS400YEARS;