1 files changed, 79 insertions, 0 deletions
diff --git a/src/nxt_gmtime.c b/src/nxt_gmtime.c
new file mode 100644
index 00000000..9c3fa190
--- /dev/null
+++ b/src/nxt_gmtime.c
@@ -0,0 +1,79 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ * Copyright (C) NGINX, Inc.
+ */
+
+#include <nxt_main.h>
+
+
+/* The function is valid for positive nxt_time_t only. */
+
+void
+nxt_gmtime(nxt_time_t s, struct tm *tm)
+{
+    nxt_int_t   yday;
+    nxt_uint_t  daytime, mday, mon, year, days, leap;
+
+    days = (nxt_uint_t) (s / 86400);
+    daytime = (nxt_uint_t) (s % 86400);
+
+    /* January 1, 1970 was Thursday. */
+    tm->tm_wday = (4 + days) % 7;
+
+    /* The algorithm based on Gauss' formula. */
+
+    /* Days since March 1, 1 BCE. */
+    days = days - (31 + 28) + 719527;
+
+    /*
+     * The "days" should be adjusted by 1 only, however some March 1st's
+     * go to previous year, so "days" are adjusted by 2.  This also shifts
+     * the last February days to the next year, but this is catched by
+     * negative "yday".
+     */
+    year = (days + 2) * 400 / (365 * 400 + 100 - 4 + 1);
+
+    yday = days - (365 * year + year / 4 - year / 100 + year / 400);
+
+    leap = (year % 4 == 0) && (year % 100 || (year % 400 == 0));
+
+    if (yday < 0) {
+        yday = 365 + leap + yday;
+        year--;
+    }
+
+    /*
+     * An empirical formula that maps "yday" to month.
+     * There are at least 10 variants, some of them are:
+     *     mon = (yday + 31) * 15 / 459
+     *     mon = (yday + 31) * 17 / 520
+     *     mon = (yday + 31) * 20 / 612
+     */
+
+    mon = (yday + 31) * 10 / 306;
+
+    /* The Gauss' formula that evaluates days before month. */
+
+    mday = yday - (367 * mon / 12 - 30) + 1;
+
+    if (yday >= 306) {
+        year++;
+        mon -= 11;
+        yday -= 306;
+
+    } else {
+        mon++;
+        yday += 31 + 28 + leap;
+    }
+
+    tm->tm_mday = mday;
+    tm->tm_mon = mon;
+    tm->tm_year = year - 1900;
+    tm->tm_yday = yday;
+
+    tm->tm_hour = daytime / 3600;
+    daytime %= 3600;
+    tm->tm_min = daytime / 60;
+    tm->tm_sec = daytime % 60;
+}