Add a "fork" of musl as //fusl.

fusl/src/time/__secs_to_tm.c

+#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, years;
+        int remdays, remsecs, remyears;
+        int qc_cycles, c_cycles, q_cycles;
+        int 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 + 400LL*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;
+}