libbb: introduce and use msleep()

function                                             old     new   delta
msleep                                                 -      45     +45
watchdog_main                                        271     266      -5
common_traceroute_main                              3546    3530     -16
beep_main                                            277     248     -29
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/3 up/down: 45/-50)             Total: -5 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/bb_do_delay.c b/libbb/bb_do_delay.c
index 3a86dc2..3dbf032 100644
--- a/libbb/bb_do_delay.c
+++ b/libbb/bb_do_delay.c
@@ -8,7 +8,7 @@
  */
 #include "libbb.h"
 
-/* void FAST_FUNC bb_do_delay(int seconds) { ... } - no users yet */
+/* void FAST_FUNC bb_do_delay(unsigned seconds) { ... } - no users yet */
 
 #ifndef LOGIN_FAIL_DELAY
 #define LOGIN_FAIL_DELAY 3
@@ -34,3 +34,16 @@
 	sleep(1);
 }
 
+void FAST_FUNC msleep(unsigned ms)
+{
+	/* 1. usleep(n) is not guaranteed by standards to accept n >= 1000000
+	 * 2. multiplication in usleep(ms * 1000) can overflow if ms > 4294967
+	 *    (sleep of ~71.5 minutes)
+	 * Let's play safe and loop:
+	 */
+	while (ms > 500) {
+		usleep(500000);
+		ms -= 500;
+	}
+	usleep(ms * 1000);
+}