hle: Stub some service calls used by the home menu. (#6675)

src/core/hle/kernel/shared_page.cpp

@@ -87,8 +87,7 @@ Handler::Handler(Core::Timing& timing) : timing(timing) {
     shared_page.sliderstate_3d = static_cast<float_le>(slidestate);
 }
 
-/// Gets system time in 3DS format. The epoch is Jan 1900, and the unit is millisecond.
-u64 Handler::GetSystemTime() const {
+u64 Handler::GetSystemTimeSince2000() const {
     std::chrono::milliseconds now =
         init_time + std::chrono::duration_cast<std::chrono::milliseconds>(timing.GetGlobalTimeUs());
 
@@ -104,23 +103,25 @@ u64 Handler::GetSystemTime() const {
     epoch_tm.tm_isdst = 0;
     s64 epoch = std::mktime(&epoch_tm) * 1000;
 
-    // 3DS console time uses Jan 1 1900 as internal epoch,
-    // so we use the milliseconds between 1900 and 2000 as base console time
-    u64 console_time = 3155673600000ULL;
-
     // Only when system time is after 2000, we set it as 3DS system time
     if (now.count() > epoch) {
-        console_time += (now.count() - epoch);
+        return now.count() - epoch;
+    } else {
+        return 0;
     }
+}
 
-    return console_time;
+u64 Handler::GetSystemTimeSince1900() const {
+    // 3DS console time uses Jan 1 1900 as internal epoch,
+    // so we use the milliseconds between 1900 and 2000 as base console time
+    return 3155673600000ULL + GetSystemTimeSince2000();
 }
 
 void Handler::UpdateTimeCallback(std::uintptr_t user_data, int cycles_late) {
     DateTime& date_time =
         shared_page.date_time_counter % 2 ? shared_page.date_time_0 : shared_page.date_time_1;
 
-    date_time.date_time = GetSystemTime();
+    date_time.date_time = GetSystemTimeSince1900();
     date_time.update_tick = timing.GetTicks();
     date_time.tick_to_second_coefficient = BASE_CLOCK_RATE_ARM11;
     date_time.tick_offset = 0;

src/core/hle/kernel/shared_page.h

@@ -110,8 +110,13 @@ public:
         return sizeof(shared_page);
     }
 
+    /// Gets the system time in milliseconds since the year 2000.
+    u64 GetSystemTimeSince2000() const;
+
+    /// Gets the system time in milliseconds since the year 1900.
+    u64 GetSystemTimeSince1900() const;
+
 private:
-    u64 GetSystemTime() const;
     void UpdateTimeCallback(std::uintptr_t user_data, int cycles_late);
     Core::Timing& timing;
     Core::TimingEventType* update_time_event;