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.
This commit is contained in:
Greg Reagle 2015-01-08 17:16:19 -05:00 committed by sin
parent 7a58d65483
commit 6c2074560e
3 changed files with 42 additions and 14 deletions

2
README
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@ -9,7 +9,7 @@ The following tools are implemented (* == finished):
UTILITY POSIX 2008 COMPLIANT MISSING OPTIONS UTILITY POSIX 2008 COMPLIANT MISSING OPTIONS
------- -------------------- --------------- ------- -------------------- ---------------
* basename yes none * basename yes none
cal pending pending cal yes none
* cat yes none * cat yes none
chgrp no -h, -H, -L, -P chgrp no -h, -H, -L, -P
chmod yes none chmod yes none

3
cal.1
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@ -28,6 +28,7 @@ of calendars side by side. Each row of calendars contains at most
.IR columns .IR columns
number of calendars. The defaults are obtained using number of calendars. The defaults are obtained using
.IR localtime (3). .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 .SH OPTIONS
.TP .TP
.B \-1 .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. Specify the number months to print. The default is 1.
.SH SEE ALSO .SH SEE ALSO
.IR localtime (3) .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.

51
cal.c
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@ -5,41 +5,61 @@
#include "util.h" #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 static int
isleap(int year) isleap(int year, enum caltype cal)
{ {
if (year % 400 == 0) if (cal == Gregorian) {
return 1; if (year % 400 == 0)
if (year % 100 == 0) return 1;
return 0; if (year % 100 == 0)
return (year % 4 == 0); return 0;
return (year % 4 == 0);
}
else { /* cal == Julian */
return (year % 4 == 0);
}
} }
static int 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 }; 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 */ /* From http://www.tondering.dk/claus/cal/chrweek.php#calcdow */
static int static int
dayofweek(int year, int month, int dom) dayofweek(int year, int month, int dom, enum caltype cal)
{ {
int m, y, a; int m, y, a;
month += 1; /* in this formula, 1 <= month <= 12 */ month += 1; /* in this formula, 1 <= month <= 12 */
a = (14 - month) / 12; a = (14 - month) / 12;
y = year - a; y = year - a;
m = month + 12*a - 2; 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 static void
printgrid(int year, int month, int fday, int line) printgrid(int year, int month, int fday, int line)
{ {
int dom, offset, d=0; enum caltype cal;
int trans; /* are we in the transition from Julian to Gregorian? */
int offset, dom, d=0;
offset = dayofweek(year, month, 1) - fday; 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) if (offset < 0)
offset += 7; offset += 7;
if (line==1) { if (line==1) {
@ -48,9 +68,14 @@ printgrid(int year, int month, int fday, int line)
dom = 1; dom = 1;
} else { } else {
dom = 8-offset + (line-2)*7; 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); printf("%2d ", dom);
if (trans && dom==TRANS_DAY)
dom += 11;
}
for ( ; d < 7; ++d) for ( ; d < 7; ++d)
printf(" "); printf(" ");
} }