libc: Add difftime()

libs/libc/include/time.h

@@ -77,6 +77,9 @@ extern "C"
     /* Fills str with a formatted string representation of time according to the format string. */
     size_t strftime(char* str, size_t max, const char* format, const struct tm* time);
 
+    /* Returns the difference between two times. */
+    double difftime(time_t time2, time_t time1);
+
 #ifdef __cplusplus
 }
 #endif

libs/libc/src/time.cpp

@@ -175,4 +175,9 @@ extern "C"
     {
         return broken_down_to_unix(time->tm_year, time->tm_yday, time->tm_hour, time->tm_min, time->tm_sec);
     }
+
+    double difftime(time_t time2, time_t time1)
+    {
+        return (double)(time2 - time1);
+    }
 }