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Use the Julian/Gregorian calendar

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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
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51
cal.c
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@@ -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;
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)
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(" ");
}