56 lines
1.6 KiB
C
56 lines
1.6 KiB
C
/* +++Date last modified: 05-Jul-1997 */
|
|
|
|
/*
|
|
** scalar date routines -- public domain by Ray Gardner
|
|
** Numerically, these will work over the range 1/01/01 thru 14699/12/31.
|
|
** Practically, these only work from the beginning of the Gregorian
|
|
** calendar thru 14699/12/31. The Gregorian calendar took effect in
|
|
** much of Europe in about 1582, some parts of Germany in about 1700, in
|
|
** England and the colonies in about 1752ff, and in Russia in 1918.
|
|
*/
|
|
|
|
#include "scaldate.h"
|
|
|
|
int isleap (unsigned yr)
|
|
{
|
|
return yr % 400 == 0 || (yr % 4 == 0 && yr % 100 != 0);
|
|
}
|
|
|
|
static unsigned months_to_days (unsigned month)
|
|
{
|
|
return (month * 3057 - 3007) / 100;
|
|
}
|
|
|
|
static long years_to_days (unsigned yr)
|
|
{
|
|
return yr * 365L + yr / 4 - yr / 100 + yr / 400;
|
|
}
|
|
|
|
long ymd_to_scalar (unsigned yr, unsigned mo, unsigned day)
|
|
{
|
|
long scalar;
|
|
scalar = day + months_to_days(mo);
|
|
if ( mo > 2 ) /* adjust if past February */
|
|
scalar -= isleap(yr) ? 1 : 2;
|
|
yr--;
|
|
scalar += years_to_days(yr);
|
|
return scalar;
|
|
}
|
|
|
|
void scalar_to_ymd (long scalar, unsigned *yr, unsigned *mo, unsigned *day)
|
|
{
|
|
unsigned n; /* compute inverse of years_to_days() */
|
|
|
|
for ( n = (unsigned)((scalar * 400L) / 146097L); years_to_days(n) < scalar;)
|
|
n++; /* 146097 == years_to_days(400) */
|
|
*yr = n;
|
|
n = (unsigned)(scalar - years_to_days(n-1));
|
|
if ( n > 59 ) { /* adjust if past February */
|
|
n += 2;
|
|
if ( isleap(*yr) )
|
|
n -= n > 62 ? 1 : 2;
|
|
}
|
|
*mo = (n * 100 + 3007) / 3057; /* inverse of months_to_days() */
|
|
*day = n - months_to_days(*mo);
|
|
}
|