diff --git a/System/FFI/LibC.HC b/System/FFI/LibC.HC
index d089d7a..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;
@@ -241,7 +315,6 @@ U0 strcmp()
 {
     PUSH_SYSV_REGS
     GET_SYSV_ARGS
-    //"strcmp: '%s', '%s'\n", p0, p1;
     StrCmp(p0, p1);
     POP_SYSV_REGS
 }
@@ -291,14 +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;
@@ -385,11 +450,3 @@ U0 strstr()
     POP_SYSV_REGS
 
 }
-
-U0 sprintf()
-{
-    PUSH_SYSV_REGS
-    GET_SYSV_ARGS
-    StrPrint(p0, p1, p2, p3, p4, p5);
-    POP_SYSV_REGS
-}
diff --git a/src/mujs/jsdate.c b/src/mujs/jsdate.c
index bf1d406..fd5ab46 100644
--- a/src/mujs/jsdate.c
+++ b/src/mujs/jsdate.c
@@ -323,7 +323,7 @@ static char *fmtdate(char *buf, double t)
 	int d = DateFromTime(t);
 	if (!isfinite(t))
 		return "Invalid Date";
-	sprintf(buf, "%04d-%02d-%02d", y, m+1, d);
+	npf_snprintf(buf, 1024, "%04d-%02d-%02d", y, m+1, d);
 	return buf;
 }
 
@@ -338,11 +338,11 @@ static char *fmttime(char *buf, double t, double tza)
 	if (!isfinite(t))
 		return "Invalid Date";
 	if (tza == 0)
-		sprintf(buf, "%02d:%02d:%02d.%03dZ", H, M, S, ms);
+		npf_snprintf(buf, 1024, "%02d:%02d:%02d.%03dZ", H, M, S, ms);
 	else if (tza < 0)
-		sprintf(buf, "%02d:%02d:%02d.%03d-%02d:%02d", H, M, S, ms, tzh, tzm);
+		npf_snprintf(buf, 1024, "%02d:%02d:%02d.%03d-%02d:%02d", H, M, S, ms, tzh, tzm);
 	else
-		sprintf(buf, "%02d:%02d:%02d.%03d+%02d:%02d", H, M, S, ms, tzh, tzm);
+		npf_snprintf(buf, 1024, "%02d:%02d:%02d.%03d+%02d:%02d", H, M, S, ms, tzh, tzm);
 	return buf;
 }
 
@@ -353,7 +353,7 @@ static char *fmtdatetime(char *buf, double t, double tza)
 		return "Invalid Date";
 	fmtdate(dbuf, t);
 	fmttime(tbuf, t, tza);
-	sprintf(buf, "%sT%s", dbuf, tbuf);
+	npf_snprintf(buf, 1024, "%sT%s", dbuf, tbuf);
 	return buf;
 }
 
diff --git a/src/mujs/jsnumber.c b/src/mujs/jsnumber.c
index 8e79d34..86259da 100644
--- a/src/mujs/jsnumber.c
+++ b/src/mujs/jsnumber.c
@@ -116,11 +116,11 @@ static void numtostr(js_State *J, const char *fmt, int w, double n)
 {
 	/* buf needs to fit printf("%.20f", 1e20) */
 	char buf[50], *e;
-	sprintf(buf, fmt, w, n);
+	npf_snprintf(buf, 1024, fmt, w, n);
 	e = strchr(buf, 'e');
 	if (e) {
 		int exp = atoi(e+1);
-		sprintf(e, "e%+d", exp);
+		npf_snprintf(e, 1024, "e%+d", exp);
 	}
 	js_pushstring(J, buf);
 }
diff --git a/src/mujs/jsrun.c b/src/mujs/jsrun.c
index b956208..e06b212 100644
--- a/src/mujs/jsrun.c
+++ b/src/mujs/jsrun.c
@@ -919,11 +919,11 @@ const char *js_ref(js_State *J)
 		s = v->u.boolean ? "_True" : "_False";
 		break;
 	case JS_TOBJECT:
-		sprintf(buf, "%p", (void*)v->u.object);
+		npf_snprintf(buf, 1024, "%p", (void*)v->u.object);
 		s = js_intern(J, buf);
 		break;
 	default:
-		sprintf(buf, "%d", J->nextref++);
+		npf_snprintf(buf, 1024, "%d", J->nextref++);
 		s = js_intern(J, buf);
 		break;
 	}