Kernel: Correctly calculate delta_ticks when 64-bit counter wraps around

We never caught this bug in the HPET, since it takes ages for a 64-bit
counter to wrap around. Also remove an unnecessary if check.

1 files changed, 8 insertions, 8 deletions

diff --git a/Kernel/Arch/x86/Time/HPET.cpp b/Kernel/Arch/x86/Time/HPET.cpp
index 725d767bd5..fc470a7a84 100644
--- a/Kernel/Arch/x86/Time/HPET.cpp
+++ b/Kernel/Arch/x86/Time/HPET.cpp
@@ -262,18 +262,18 @@ u64 HPET::update_time(u64& seconds_since_boot, u32& ticks_this_second, bool quer
         delta_ticks += current_value - m_main_counter_last_read;
     } else {
         // the counter wrapped around
-        delta_ticks += m_main_counter_last_read - current_value;
-        if (!m_main_counter_64bits)
+        if (m_main_counter_64bits) {
+            delta_ticks += (NumericLimits<u64>::max() - m_main_counter_last_read + 1) + current_value;
+        } else {
+            delta_ticks += (NumericLimits<u32>::max() - m_main_counter_last_read + 1) + current_value;
             m_32bit_main_counter_wraps++;
+        }
     }
+
     u64 ticks_since_last_second = (u64)ticks_this_second + delta_ticks;
     auto ticks_per_second = frequency();
-    if (ticks_since_last_second >= ticks_per_second) {
-        seconds_since_boot += ticks_since_last_second / ticks_per_second;
-        ticks_this_second = ticks_since_last_second % ticks_per_second;
-    } else {
-        ticks_this_second = ticks_since_last_second;
-    }
+    seconds_since_boot += ticks_since_last_second / ticks_per_second;
+    ticks_this_second = ticks_since_last_second % ticks_per_second;
 
     if (!query_only) {
         m_main_counter_drift = 0;