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C/C++ Users Group Library 1996 July
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C-C++ Users Group Library July 1996.iso
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v_11_02
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1102014a
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1992-12-07
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/* _Ttotm and _Daysto functions */
#include "xtime.h"
/* macros */
#define MONTAB(year) \
((year) & 03 || (year) == 0 ? mos : lmos)
/* static data */
static const short lmos[] = {0, 31, 60, 91, 121, 152,
182, 213, 244, 274, 305, 335};
static const short mos[] = {0, 31, 59, 90, 120, 151,
181, 212, 243, 273, 304, 334};
int _Daysto(int year, int mon)
{ /* compute extra days to start of month */
int days;
if (0 < year) /* correct for leap year:
1801-2099 */
days = (year - 1) / 4;
else if (year <= -4)
days = 1 + (4 - year) / 4;
else
days = 0;
return (days + MONTAB(year)[mon]);
}
struct tm *_Ttotm(struct tm *t, time_t secsarg, int isdst)
{ /* convert scalar time to time structure */
int year;
long days;
time_t secs;
static struct tm ts;
secsarg += _TBIAS;
if (t == NULL)
t = &ts;
t->tm_isdst = isdst;
for (secs = secsarg; ; secs = secsarg + 3600)
{ /* loop to correct for DST */
days = secs / 86400;
t->tm_wday = (days + WDAY) % 7;
{ /* determine year */
long i;
for (year = days / 365; days <
(i = _Daysto(year, 0) + 365L * year); )
--year; /* correct guess and recheck */
days -= i;
t->tm_year = year;
t->tm_yday = days;
}
{ /* determine month */
int mon;
const short *pm = MONTAB(year);
for (mon = 12; days < pm[--mon]; )
;
t->tm_mon = mon;
t->tm_mday = days - pm[mon] + 1;
}
secs %= 86400;
t->tm_hour = secs / 3600;
secs %= 3600;
t->tm_min = secs / 60;
t->tm_sec = secs % 60;
if (0 <= t->tm_isdst ||
(t->tm_isdst = _Isdst(t)) <= 0)
return (t); /* loop only if <0 => 1 */
}
}