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Files correlati : Ricompilazione Demo : [ ] Commento : Aggiunti i sorgenti per Greenleaf Math Library (gfm.dll) git-svn-id: svn://10.65.10.50/trunk@10079 c028cbd2-c16b-5b4b-a496-9718f37d4682
144 lines
4.1 KiB
C
Executable File
144 lines
4.1 KiB
C
Executable File
/* int DaysBetweenDates365(m1,d1,y1, m2,d2,y2)
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*
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* ARGUMENT
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* int m1,d1,y1; - Base Date
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* int m2,d2,y2; - Date to compare with base
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*
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* DESCRIPTION
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* Compares two dates in date args format, forming the difference in
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* whole days. The result is a signed number:
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*
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* 0 if dates are same,
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* +n if date1 > date2
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* -n if date1 < date2
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*
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* SIDE EFFECTS
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* None.
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*
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* RETURNS
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* +,-, or 0 days. 0 can indicate an error.
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*
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* POSSIBLE ERROR CODES
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* GM_ARGVAL
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* GM_OVERFLOW
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*
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* AUTHOR
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* 05-Aug-1987 12:43:39
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* Copyright (C) 1987-1990 Greenleaf Software Inc. All rights reserved.
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*
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* MODIFICATIONS
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*
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* 01-Jan-1989 Corrected for true Gregorian Calendar
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*
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* DISCUSSION
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*
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* It may not be entirely clear when reading this code just what is going
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* on. First of all, the calendar used is the Greenleaf version of the
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* Gregorian calendar. We assume in this calendar that Gregorian time
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* extends backwards to the year 0, and forward forever, more or less.
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* A leap year occurs every four years. Except when the year is evenly
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* divisible by 100, like the year 1900, when there is no leap year. Except
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* when the year is evenly divisible by 400, in which case there really
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* is a leap year.
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*
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* The way this algorithm works is relatively simple. There are four
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* mysterious variables in this program: n1, n2, x and z. n1 and n2 are
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* relatively easy to understand. These variables are simple the number
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* of days since January 1, year 0. The difference between these two numbers
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* is the actual number returned by this function.
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*
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* In order to calculate the number of days since 1/1/0, we can start by
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* adding 365 days per year:
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*
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* n = 365 * y
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*
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* This gets a pretty good rough number, but it doesn't take into account
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* the leap years. Given the Greenleaf Gregorian calendar, we can add in
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* all the days accounted for by leap years like this:
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*
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* n = 365 * y + y/4 - y/100 + y/400
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*
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* This works pretty well, but it leaves us with one problem: we are
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* adding in a leap day in leap years, even if the month is January
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* or February. On January 1, 1984, we haven't hit the leap day yet, so
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* we shouldn't add it in. This is where z comes from. y is the actual
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* year, but z is the year used for calculation of leap days:
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*
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* if ( m <= 2 )
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* z = y - 1;
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* else
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* z = y;
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* n = 365 * y + y/4 - y/100 + y/400
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*
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* At this point, n is accurate for January 1 of the given year. Now we
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* have to add in the days accounted for by the months in the selected year.
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* A good guess on how to do this is to just add 31 days per month:
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*
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* n = 365 * y + y/4 - y/100 + y/400 + 31*(m - 1)
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*
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* The only problem is that starting with month 3, there will be errors
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* in the calculation. The good news is that a simple formula will generate
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* a correction factor, which is x. The formula for x is (4*m + 23) / 10.
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* This just happens to generate the correct sequence of numbers. A different
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* way would be to create an x array {0, 0, 3, 3, 4, 4, 5, 5, 5, 6, 6, 7};
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* So now my formula looks like this:
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*
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* if ( m <= 2 ) {
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* x = 0;
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* z = y - 1;
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* } else {
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* z = y;
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* x = ( 4 * m + 23 ) / 10 ;
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* }
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* n = 365 * y + y/4 - y/100 + y/400 + 31*(m - 1)
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*
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* The final step is to add in the day of the month, to account for all the
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* days in the current month. Do that and you are done.
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*
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*/
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#include <stdio.h>
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#include "gmsystem.h"
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int DaysBetweenDates365(m1,d1,y1,m2,d2,y2)
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int m1,d1,y1,m2,d2,y2;
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{
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long n1, n2, n;
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int x, z;
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_MacStart(GM_DBD365);
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if (m1<1||m1>12||d1<1||d1>31||y1<0||y1>9999||
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m2<1||m2>12||d2<1||d2>31||y2<0||y2>9999) {
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_MacErr(GM_ARGVAL);
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_MacRet(GM_ARGVAL);
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}
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if (m1<=2) {
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x=0;
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z=y1-1;
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} else {
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x=(4*m1 + 23) / 10;
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z=y1;
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}
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n1 = (long) y1 * 365L + (long) (31*(m1-1) + d1 + z/4 - z/100 + z/400 - x);
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if (m2<=2) {
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x=0;
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z=y2-1;
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} else {
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x=(4*m2 + 23) / 10;
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z=y2;
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}
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n2 = (long) y2 * 365L + (long) (31*(m2-1) + d2 + z/4 - z/100 + z/400 - x);
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n = n1 - n2;
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if (n<-32768L||n>32767L) {
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_MacErr(GM_OVERFLOW);
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_MacRet(GM_OVERFLOW);
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}
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_MacRet((int) n);
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}
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