udhcp: protect agianst timer overflowing 32-bit counter

function                                             old     new   delta
arpping                                              398     387     -11

diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index 45597c04b00ad6d25108f399685bbe4c436480a5..a8a458468f1c2b40870acfcf8b1923098999c906 100644 (file)
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -106,7 +106,7 @@ int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *i
                                break;
                        }
                }
-               timeout_ms -= (monotonic_us() - prevTime) / 1000;
+               timeout_ms -= ((unsigned)monotonic_us() - prevTime) / 1000;
        } while (timeout_ms > 0);
 
  ret: