diff --git a/System/FFI/LibC.HC b/System/FFI/LibC.HC
index 2f1fe23..f26949f 100644
--- a/System/FFI/LibC.HC
+++ b/System/FFI/LibC.HC
@@ -51,6 +51,30 @@ _LONGJMP::
 _extern _SETJMP U64 _setjmp(U64 jmp_buf);
 _extern _LONGJMP U64 longjmp(U64 jmp_buf, U64 ret);
 
+class libc_tm {
+    I32 tm_sec;         /* seconds,  range 0 to 59          */
+    I32 tm_min;         /* minutes, range 0 to 59           */
+    I32 tm_hour;        /* hours, range 0 to 23             */
+    I32 tm_mday;        /* day of the month, range 1 to 31  */
+    I32 tm_mon;         /* month, range 0 to 11             */
+    I32 tm_year;        /* The number of years since 1900   */
+    I32 tm_wday;        /* day of the week, range 0 to 6    */
+    I32 tm_yday;        /* day in the year, range 0 to 365  */
+    I32 tm_isdst;       /* daylight saving time             */
+};
+
+#define NIST_TIME_OFFSET -9488
+
+I64 CDate2Unix(CDate dt)
+{ // TempleOS datetime to Unix timestamp.
+    return ToI64((dt - Str2Date("1/1/1970")) / CDATE_FREQ + NIST_TIME_OFFSET);
+}
+
+public CDate Unix2CDate(I64 timestamp)
+{//Unix timestamp to TempleOS datetime.
+    return (timestamp-NIST_TIME_OFFSET)*CDATE_FREQ+Str2Date("1/1/1970");
+}
+
 U0 free()
 {
     PUSH_SYSV_REGS
@@ -82,6 +106,56 @@ U0 localtime()
     POP_SYSV_REGS
 }
 
+U64 @gmtime(U64* timep)
+{
+    CDateStruct ds;
+    Date2Struct(&ds, Unix2CDate(*timep));
+    libc_tm* tm = CAlloc(sizeof(libc_tm));
+
+    tm->tm_sec = ds.sec;
+    tm->tm_min = ds.min;
+    tm->tm_hour = ds.hour;
+    tm->tm_mday = ds.day_of_mon;
+    tm->tm_mon = ds.mon;
+    tm->tm_year = ds.year;
+    tm->tm_wday = ds.day_of_week;
+    return tm;
+}
+
+U0 gmtime()
+{
+    PUSH_SYSV_REGS
+    GET_SYSV_ARGS
+    @gmtime(p0);
+    POP_SYSV_REGS
+}
+
+U64 @mktime(libc_tm* tm)
+{
+    CDateStruct ds;
+    MemSet(&ds, 0, sizeof(CDateStruct));
+    if (tm) {
+        ds.sec = tm->tm_sec;
+        ds.min = tm->tm_min;
+        ds.hour = tm->tm_hour;
+        ds.day_of_mon = tm->tm_mday;
+        ds.mon = tm->tm_mon;
+        ds.year = tm->tm_year;
+        ds.day_of_week = tm->tm_wday;
+    } else {
+        Date2Struct(&ds, Now);
+    }
+    return CDate2Unix(Struct2Date(&ds));
+}
+
+U0 mktime()
+{
+    PUSH_SYSV_REGS
+    GET_SYSV_ARGS
+    @mktime(p0);
+    POP_SYSV_REGS
+}
+
 I64 @strncmp(U8* s1, U8* s2, I32 n)
 {
     U64 u1, u2;
@@ -290,14 +364,6 @@ U0 realloc()
     POP_SYSV_REGS
 }
 
-#define MY_TIME_OFFSET 9488
-
-public
-I64 CDate2Unix(CDate dt)
-{ // TempleOS datetime to Unix timestamp.
-    return ToI64((dt - Str2Date("1/1/1970")) / CDATE_FREQ) - MY_TIME_OFFSET;
-}
-
 I64 @time(I64* ptr)
 {
     no_warn ptr;