commit 6c2074560efe07b5b8c357e4b2bb306502419197
parent 7a58d65483124c4866d8294de490ebe766b283db
Author: Greg Reagle <greg.reagle@umbc.edu>
Date: Thu, 8 Jan 2015 17:16:19 -0500
Use the Julian/Gregorian calendar
Use the Julian calendar for dates through September 2, 1752 and
the Gregorian calendar for dates from September 14, 1752.
Diffstat:
| M | README | | | 2 | +- |
| M | cal.1 | | | 3 | +++ |
| M | cal.c | | | 53 | +++++++++++++++++++++++++++++++++++++++-------------- |
3 files changed, 43 insertions(+), 15 deletions(-)
diff --git a/README b/README
@@ -9,7 +9,7 @@ The following tools are implemented (* == finished):
UTILITY POSIX 2008 COMPLIANT MISSING OPTIONS
------- -------------------- ---------------
* basename yes none
- cal pending pending
+ cal yes none
* cat yes none
chgrp no -h, -H, -L, -P
chmod yes none
diff --git a/cal.1 b/cal.1
@@ -28,6 +28,7 @@ of calendars side by side. Each row of calendars contains at most
.IR columns
number of calendars. The defaults are obtained using
.IR localtime (3).
+The Julian calendar is used through Sep 2, 1752, and the Gregorian calendar is used starting the next day with Sep 14, 1752.
.SH OPTIONS
.TP
.B \-1
@@ -57,3 +58,5 @@ Specify the first day of the week. 0 is Sunday and 6 is Saturday.
Specify the number months to print. The default is 1.
.SH SEE ALSO
.IR localtime (3)
+.SH STANDARDS
+This program tries to conform to IEEE Std 1003.1, 2013 Edition, q.v. http://pubs.opengroup.org/onlinepubs/9699919799/utilities/cal.html.
diff --git a/cal.c b/cal.c
@@ -5,41 +5,61 @@
#include "util.h"
+enum {Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec};
+enum caltype {Julian, Gregorian};
+enum {TRANS_YEAR = 1752, TRANS_MONTH = Sep, TRANS_DAY = 2};
+
static int
-isleap(int year)
+isleap(int year, enum caltype cal)
{
- if (year % 400 == 0)
- return 1;
- if (year % 100 == 0)
- return 0;
- return (year % 4 == 0);
+ if (cal == Gregorian) {
+ if (year % 400 == 0)
+ return 1;
+ if (year % 100 == 0)
+ return 0;
+ return (year % 4 == 0);
+ }
+ else { /* cal == Julian */
+ return (year % 4 == 0);
+ }
}
static int
-monthlength(int year, int month)
+monthlength(int year, int month, enum caltype cal)
{
int mdays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
- return (month==1 && isleap(year)) ? 29 : mdays[month];
+ return (month==Feb && isleap(year,cal)) ? 29 : mdays[month];
}
/* From http://www.tondering.dk/claus/cal/chrweek.php#calcdow */
static int
-dayofweek(int year, int month, int dom)
+dayofweek(int year, int month, int dom, enum caltype cal)
{
int m, y, a;
month += 1; /* in this formula, 1 <= month <= 12 */
a = (14 - month) / 12;
y = year - a;
m = month + 12*a - 2;
- return (dom + y + y/4 - y/100 + y/400 +((31*m)/12)) % 7;
+
+ if (cal == Gregorian)
+ return (dom + y + y/4 - y/100 + y/400 + (31*m)/12) % 7;
+ else /* cal == Julian */
+ return (5 + dom + y + y/4 + (31*m)/12) % 7;
}
static void
printgrid(int year, int month, int fday, int line)
{
- int dom, offset, d=0;
-
- offset = dayofweek(year, month, 1) - fday;
+ enum caltype cal;
+ int trans; /* are we in the transition from Julian to Gregorian? */
+ int offset, dom, d=0;
+
+ if (year < TRANS_YEAR || (year == TRANS_YEAR && month <= TRANS_MONTH))
+ cal = Julian;
+ else
+ cal = Gregorian;
+ trans = (year == TRANS_YEAR && month == TRANS_MONTH);
+ offset = dayofweek(year, month, 1, cal) - fday;
if (offset < 0)
offset += 7;
if (line==1) {
@@ -48,9 +68,14 @@ printgrid(int year, int month, int fday, int line)
dom = 1;
} else {
dom = 8-offset + (line-2)*7;
+ if (trans && !(line==2 && fday==3))
+ dom += 11;
}
- for ( ; d < 7 && dom <= monthlength(year, month); ++d, ++dom)
+ for ( ; d < 7 && dom <= monthlength(year, month, cal); ++d, ++dom) {
printf("%2d ", dom);
+ if (trans && dom==TRANS_DAY)
+ dom += 11;
+ }
for ( ; d < 7; ++d)
printf(" ");
}
