Merge pull request #4422 from mysterywolf/libctime

[libc] remove difftime()

components/libc/compilers/common/time.c

@@ -12,7 +12,6 @@
  * 2021-02-08     Meco Man     add settimeofday() stime()
  * 2021-02-10     Meco Man     add ctime_r() and re-implement ctime()
  * 2021-02-11     Meco Man     fix bug #3183 - align days[] and months[] to 4 bytes
- *                             add difftime()
  * 2021-02-12     Meco Man     add errno
  * 2012-12-08     Bernard      <clock_time.c> fix the issue of _timevalue.tv_usec initialization,
  *                             which found by Rob <rdent@iinet.net.au>
@@ -177,12 +176,6 @@ char* ctime(const time_t *tim_p)
 }
 RTM_EXPORT(ctime);
 
-double difftime (time_t tim1, time_t tim2)
-{
-    return (double)(tim1 - tim2);
-}
-RTM_EXPORT(difftime);
-
 /**
  * Returns the current time.
  *
@@ -372,6 +365,10 @@ int settimeofday(const struct timeval *tv, const struct timezone *tz)
 }
 RTM_EXPORT(settimeofday);
 
+/* inherent in the toolchain */
+RTM_EXPORT(difftime); 
+RTM_EXPORT(strftime);
+
 #ifdef RT_USING_POSIX
 static struct timeval _timevalue;
 static int clock_time_system_init()