75 lines
2.5 KiB
C
75 lines
2.5 KiB
C
/* Copyright Manx Software Systems 1989. All rights reserved */
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/*
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* time_t mktime(struct tm *timeptr)
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*
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* converts the broken-down time, expressed as local time, in the
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* structure pointed to by timeptr into a calendar time value with
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* the same encoding as that of the values returned by the time
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* function. The original values of the tm_wday and tm_yday
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* components of the structure are ignored, and the original values
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* of the other components are not restricted to the ranges
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* specified for the tm structure. On successful completion, the
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* values of the tm_wday and tm_yday components of the structure are
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* set appropriately, and the other components are set to represent
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* the specified calendar time, but with their values forced to the
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* ranges indicated for the tm structure; the final value of tm_mday
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* is not set until tm_mon and tm_year are determined.
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*
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* returns the specified calendar time encoded as a value of type
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* time_t. If the calendar time cannot be represented, the function
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* returns the value (time_t)-1.
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*/
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#include <time.h>
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#define SECS_IN_DAY (60*60*24L)
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#define YEARS_IN_GOOGLE 4 /* google is a 4 year period including leap year */
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#define DAYS_IN_GOOGLE (4*365L+1)
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#define SECS_IN_MIN 60
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#define MIN_IN_HOUR 60
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#define HOURS_IN_DAY 24
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#define SECS_IN_HOUR (60*60L)
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time_t mktime(struct tm *timeptr)
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{
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register int i, ry, ydays, year_day, years, googles;
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time_t ltime;
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static int days[12]={ 31,28,31,30,31,30,31,31,30,31,30,31 };
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if (timeptr->tm_sec < 0 || timeptr->tm_min < 0 ||
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timeptr->tm_hour < 0 || timeptr->tm_mday < 0 ||
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timeptr->tm_mon < 0 || timeptr->tm_year < 70)
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return(-1);
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ltime = timeptr->tm_sec;
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ltime += SECS_IN_MIN * timeptr->tm_min;
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ltime += SECS_IN_HOUR * timeptr->tm_hour;
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ltime += SECS_IN_DAY * (timeptr->tm_mday - 1);
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/* calculate the number of days already past in the current year */
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for (i=0,year_day=0;i<timeptr->tm_mon;i++) {
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year_day += days[i];
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if (i==1 && (timeptr->tm_year & 3) == 0)
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year_day++;
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}
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ltime += year_day * SECS_IN_DAY;
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years = timeptr->tm_year - 70;
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googles = years / YEARS_IN_GOOGLE; /* number of googles since 1970 */
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ltime+= googles * DAYS_IN_GOOGLE * SECS_IN_DAY;
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ry= 70 + YEARS_IN_GOOGLE * googles;
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/* calculate number of days since last google */
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for (i=ry, ydays=0; i < timeptr->tm_year; i++) {
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ydays += 365;
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if ((i & 3) == 0)
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ydays++;
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}
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ltime += ydays * SECS_IN_DAY;
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*timeptr = *localtime(<ime);
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return(ltime);
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}
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