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7.2
julian_proleptic_to_JD0 () |
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The routine julp2JD0.c (Listing 7.1) converts a Julian proleptic calendar date into the corresponding Julian Day number, expressed as a type double. |
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| Listing 7.1 | |
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/*
'tab2' contains the number of elapsed days prior to each month in a
common Julian year. If the year is a leap year, the table is
incremented for indices > 1 (i.e., February and after).
*/
int tab2 [12] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
long jdl;
y = jdate->year;
m = jdate->month;
d = jdate->day;
/* Intercept obviously invalid date values */
if ( (y < -4712) || (m < 1) || (m > 12) || (d < 1) || (d > 31) )
return (0.0);
/* Start with year -4712 for Julian Day number. */
y0 = y + 4712;
/*
'g4' is the number of complete groups of 4 years, each consisting of
1461 days. 'r4' is the remainder, and contains the number of complete
years (0, 1, 2 or 3) elapsed, in addition to the 4-year groups.
*/
g4 = y0 / 4;
r4 = y0 - (g4 * 4);
jdl = 1461L * (long) g4;
jdl += (long) (tab1 [r4]);
/* Increments the table for leap year. */
if ( (y % 4) == 0)
{
for (i = 2; i < 12; i++)
tab2 [i]++;
}
jdl += (long) (tab2 [m - 1]);
jdl += (long) (d - 1);
jd = (double) jdl;
return (jd);
}
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