ref: 36af8405521be371605e4658ec8f4b133f3c7d6f
dir: /sys/src/ape/lib/ap/gen/mktime.c/
#define _REENTRANT_SOURCE #include <time.h> /* * BUG: Doesn't do leap years in full glory, * or calendar changes. In 2038 the sign bit * will be needed in time_t, but we say it * can't be represented. */ static int dysize(int y) { y += 1900; /* arg is a tm_year, number of years since 1900 */ if((y%4) == 0 && ((y%100) !=0 || (y%400) == 0)) return 366; return 365; } static int dmsize(int m, int y) { static char sizes[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }; if(m == 1) return (dysize(y)==366)? 29 : 28; else return sizes[m]; } /* Reduce *v to [0, mult), adding 1 to *next for every mult * subtracted from *v, and return 1 if reduction worked (no overflow) */ static int reduce(int *v, int *next, int mult) { int oldnext; while(*v < 0){ *v += mult; oldnext = *next; --*next; if(!(*next < oldnext)) return 0; } while(*v >= mult){ *v -= mult; oldnext = *next; ++*next; if(!(*next > oldnext)) return 0; } return 1; } static int jan1(int yr) { int y, d; y = yr+1900; d = (4+y+(y+3)/4-(y-1701)/100+(y-1601)/400+3)%7; return d; } static time_t tm2sec(struct tm *t) { time_t a; int i; a = t->tm_sec; a += 60 * t->tm_min; a += 3600 * t->tm_hour; a += 86400L * t->tm_yday; if(t->tm_year < 70){ for(i=t->tm_year; i<70; i++) if((a -= dysize(i)*86400L) < 0) return -1; }else if(t->tm_year > 70){ for(i=70; i<t->tm_year; i++) if((a += dysize(i)*86400L) < 0) return -1; } return a; } time_t mktime(struct tm *t) { int i; time_t a, b; struct tm tt; if(!(reduce(&t->tm_sec, &t->tm_min, 60) && reduce(&t->tm_min, &t->tm_hour, 60) && reduce(&t->tm_hour, &t->tm_mday, 24) && reduce(&t->tm_mon, &t->tm_year, 12))) return -1; while(t->tm_mday < 1){ if(--t->tm_mon == -1){ t->tm_mon = 11; t->tm_year--; } t->tm_mday += dmsize(t->tm_mon, t->tm_year); } while(t->tm_mday > dmsize(t->tm_mon, t->tm_year)){ t->tm_mday -= dmsize(t->tm_mon, t->tm_year); if(++t->tm_mon == 12){ t->tm_mon = 0; t->tm_year++; } } t->tm_yday = t->tm_mday-1; for(i=0; i<t->tm_mon; i++) t->tm_yday += dmsize(i, t->tm_year); t->tm_wday = (jan1(t->tm_year)+t->tm_yday)%7; if((a = tm2sec(t)) != -1){ b = a; localtime_r(&a, &tt); a += (b - tm2sec(&tt)); if(t->tm_isdst < 0){ localtime_r(&a, &tt); a += (b - tm2sec(&tt)); } else if(!t->tm_isdst && tt.tm_isdst) a += 3600; else if(t->tm_isdst && !tt.tm_isdst) a -= 3600; } return a; }