1 files changed, 71 insertions, 0 deletions
diff --git a/src/time/gmtime.c b/src/time/gmtime.c
new file mode 100644
index 00000000..a844d097
--- /dev/null
+++ b/src/time/gmtime.c
@@ -0,0 +1,71 @@
+#include <time.h>
+#include "nonstd/assert.h"
+
+# define SEC_PER_MIN	(60L)
+# define MIN_PER_HR	(60L)
+# define SEC_PER_HR	((SEC_PER_MIN) * (MIN_PER_HR))
+# define HR_PER_DAY	(24L)
+# define SEC_PER_DAY	((SEC_PER_HR) * (HR_PER_DAY))
+# define DAY_PER_YEAR	(365L) /* not counting leap year */
+# define SEC_PER_YEAR	((SEC_PER_DAY) * (DAY_PER_YEAR))
+# define ISLEAPYEAR(y)	((y) % 4L == 0 && ((y) % 100L != 0 || (y) % 400L == 0))
+# define EPOCH_YEAR	(70)
+
+/** convert arithmetic time to borken down time **/
+
+struct tm * gmtime(const time_t * timer)
+{
+	static struct tm tm = {0};
+	time_t seconds = 0;
+	int days = 0;
+	int days_per_mon[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+
+	ASSERT_NONNULL(timer);
+	seconds = *timer;
+
+	tm.tm_year = EPOCH_YEAR;
+	while (seconds > SEC_PER_YEAR) {
+		/* TODO: Will this mess up Dec 31 of leap year? */
+		/* TODO: Or Jan 1 of year after leap year? */
+		seconds -= SEC_PER_YEAR;
+		if (ISLEAPYEAR(tm.tm_year + 1900)) {
+			seconds -= SEC_PER_DAY;
+		}
+		tm.tm_year++;
+	}
+	if (ISLEAPYEAR(tm.tm_year + 1900)) {
+		days_per_mon[1] = 29;
+	}
+
+	tm.tm_yday = (int)(seconds / SEC_PER_DAY);
+	seconds = seconds % SEC_PER_DAY;
+	tm.tm_hour = (int)(seconds / SEC_PER_HR);
+	seconds = seconds % SEC_PER_HR;
+	tm.tm_min = (int)(seconds / SEC_PER_MIN);
+	tm.tm_sec = (int)(seconds % SEC_PER_MIN);
+
+	days = tm.tm_yday;
+	tm.tm_mon = 0;
+	while (days > days_per_mon[tm.tm_mon]) {
+		days -= days_per_mon[tm.tm_mon];
+		tm.tm_mon++;
+	}
+	tm.tm_mday = days;
+
+	/* TODO: tm_wday */
+	tm.tm_wday = 0;
+	/* TODO: tm_isdst */
+	tm.tm_isdst = 0;
+	
+	return &tm;
+}
+
+/***
+converts the UTC time at ARGUMENT(timer) to a filled out STRUCTDEF(tm).
+***/
+
+/*
+RETURN_FAILURE(CONSTANT(NULL))
+RETURN_SUCCESS(a pointer to the converted time)
+STDC(1)
+*/