commit 91d444c2c54834cedaee34a4b35de8e5be4afce0
author George Stefan <51751981+George-Stefan@users.noreply.github.com> Mon Jan 10 23:18:49 2022 +0200
committer GitHub <noreply@github.com> Mon Jan 10 13:18:49 2022 -0800
tree fb75d5e0d9ef9a4dbe3f61d81b9cb81129548385
parent 1c3a90f9f77e2dba2d71c52040bf5524bb83ac60

[sub-mac] fix `elapsed` time in `GetCslWindowEdges()` (#7299)

Do all the calculations on uint32_t to prevent bad wraparound check
due to mixing uint32_t with uint64_t.

Signed-off-by: George Stefan <george.stefan@nxp.com>

src/core/mac/sub_mac.cpp

diff --git a/src/core/mac/sub_mac.cpp b/src/core/mac/sub_mac.cpp
index 5f9ddfd..aacef70 100644
--- a/src/core/mac/sub_mac.cpp
+++ b/src/core/mac/sub_mac.cpp
@@ -1131,20 +1131,13 @@
 void SubMac::GetCslWindowEdges(uint32_t &ahead, uint32_t &after)
 {
     uint32_t semiPeriod = mCslPeriod * kUsPerTenSymbols / 2;
-    uint64_t curTime    = otPlatRadioGetNow(&GetInstance());
-    uint64_t elapsed;
+    uint32_t curTime    = static_cast<uint32_t>(otPlatRadioGetNow(&GetInstance()));
+    uint32_t elapsed;
     uint32_t semiWindow;
 
-    if (mCslLastSync.GetValue() > curTime)
-    {
-        elapsed = UINT64_MAX - mCslLastSync.GetValue() + curTime;
-    }
-    else
-    {
-        elapsed = curTime - mCslLastSync.GetValue();
-    }
+    elapsed = curTime - mCslLastSync.GetValue();
 
-    semiWindow = static_cast<uint32_t>(elapsed * (Get<Radio>().GetCslAccuracy() + mCslParentAccuracy) / 1000000);
+    semiWindow = elapsed * (Get<Radio>().GetCslAccuracy() + mCslParentAccuracy) / 1000000;
     semiWindow += mCslParentUncert * kUsPerUncertUnit;
 
     ahead = (semiWindow + kCslReceiveTimeAhead > semiPeriod) ? semiPeriod : semiWindow + kCslReceiveTimeAhead;