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