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-rw-r--r--src/time/__secs_to_tm.c81
1 files changed, 81 insertions, 0 deletions
diff --git a/src/time/__secs_to_tm.c b/src/time/__secs_to_tm.c
new file mode 100644
index 00000000..f3c1cf92
--- /dev/null
+++ b/src/time/__secs_to_tm.c
@@ -0,0 +1,81 @@
+#include "time_impl.h"
+#include <limits.h>
+
+/* 2000-03-01 (mod 400 year, immediately after feb29 */
+#define LEAPOCH (946684800LL + 86400*(31+29))
+
+#define DAYS_PER_400Y (365*400 + 97)
+#define DAYS_PER_100Y (365*100 + 24)
+#define DAYS_PER_4Y (365*4 + 1)
+
+int __secs_to_tm(long long t, struct tm *tm)
+{
+ long long days, secs;
+ int remdays, remsecs, remyears;
+ int qc_cycles, c_cycles, q_cycles;
+ int years, months;
+ int wday, yday, leap;
+ static const char days_in_month[] = {31,30,31,30,31,31,30,31,30,31,31,29};
+
+ /* Reject time_t values whose year would overflow int */
+ if (t < INT_MIN * 31622400LL || t > INT_MAX * 31622400LL)
+ return -1;
+
+ secs = t - LEAPOCH;
+ days = secs / 86400;
+ remsecs = secs % 86400;
+ if (remsecs < 0) {
+ remsecs += 86400;
+ days--;
+ }
+
+ wday = (3+days)%7;
+ if (wday < 0) wday += 7;
+
+ qc_cycles = days / DAYS_PER_400Y;
+ remdays = days % DAYS_PER_400Y;
+ if (remdays < 0) {
+ remdays += DAYS_PER_400Y;
+ qc_cycles--;
+ }
+
+ c_cycles = remdays / DAYS_PER_100Y;
+ if (c_cycles == 4) c_cycles--;
+ remdays -= c_cycles * DAYS_PER_100Y;
+
+ q_cycles = remdays / DAYS_PER_4Y;
+ if (q_cycles == 25) q_cycles--;
+ remdays -= q_cycles * DAYS_PER_4Y;
+
+ remyears = remdays / 365;
+ if (remyears == 4) remyears--;
+ remdays -= remyears * 365;
+
+ leap = !remyears && (q_cycles || !c_cycles);
+ yday = remdays + 31 + 28 + leap;
+ if (yday >= 365+leap) yday -= 365+leap;
+
+ years = remyears + 4*q_cycles + 100*c_cycles + 400*qc_cycles;
+
+ for (months=0; days_in_month[months] <= remdays; months++)
+ remdays -= days_in_month[months];
+
+ if (years+100 > INT_MAX || years+100 < INT_MIN)
+ return -1;
+
+ tm->tm_year = years + 100;
+ tm->tm_mon = months + 2;
+ if (tm->tm_mon >= 12) {
+ tm->tm_mon -=12;
+ tm->tm_year++;
+ }
+ tm->tm_mday = remdays + 1;
+ tm->tm_wday = wday;
+ tm->tm_yday = yday;
+
+ tm->tm_hour = remsecs / 3600;
+ tm->tm_min = remsecs / 60 % 60;
+ tm->tm_sec = remsecs % 60;
+
+ return 0;
+}