Merge pull request #5964 from bunnei/timing-fix

common: wall_clock: Fix integer overflow with StandardWallClock.

2 files changed, 28 insertions, 7 deletions

diff --git a/src/common/uint128.h b/src/common/uint128.h
index 83560a9ce..4780b2f9d 100644
--- a/src/common/uint128.h
+++ b/src/common/uint128.h
@@ -98,4 +98,24 @@ namespace Common {
 #endif
 }
 
+// This function divides a u128 by a u32 value and produces two u64 values:
+// the result of division and the remainder
+[[nodiscard]] static inline std::pair<u64, u64> Divide128On32(u128 dividend, u32 divisor) {
+    u64 remainder = dividend[0] % divisor;
+    u64 accum = dividend[0] / divisor;
+    if (dividend[1] == 0)
+        return {accum, remainder};
+    // We ignore dividend[1] / divisor as that overflows
+    const u64 first_segment = (dividend[1] % divisor) << 32;
+    accum += (first_segment / divisor) << 32;
+    const u64 second_segment = (first_segment % divisor) << 32;
+    accum += (second_segment / divisor);
+    remainder += second_segment % divisor;
+    if (remainder >= divisor) {
+        accum++;
+        remainder -= divisor;
+    }
+    return {accum, remainder};
+}
+
 } // namespace Common
diff --git a/src/common/wall_clock.cpp b/src/common/wall_clock.cpp
index 1545993bd..49830b8ab 100644
--- a/src/common/wall_clock.cpp
+++ b/src/common/wall_clock.cpp
@@ -20,9 +20,7 @@ using base_time_point = std::chrono::time_point<base_timer>;
 class StandardWallClock final : public WallClock {
 public:
     explicit StandardWallClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_)
-        : WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, false),
-          emulated_clock_factor{GetFixedPoint64Factor(emulated_clock_frequency, 1000000000)},
-          emulated_cpu_factor{GetFixedPoint64Factor(emulated_cpu_frequency, 1000000000)} {
+        : WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, false) {
         start_time = base_timer::now();
     }
 
@@ -45,11 +43,16 @@ public:
     }
 
     u64 GetClockCycles() override {
-        return MultiplyHigh(GetTimeNS().count(), emulated_clock_factor);
+        std::chrono::nanoseconds time_now = GetTimeNS();
+        const u128 temporary =
+            Common::Multiply64Into128(time_now.count(), emulated_clock_frequency);
+        return Common::Divide128On32(temporary, 1000000000).first;
     }
 
     u64 GetCPUCycles() override {
-        return MultiplyHigh(GetTimeNS().count(), emulated_cpu_factor);
+        std::chrono::nanoseconds time_now = GetTimeNS();
+        const u128 temporary = Common::Multiply64Into128(time_now.count(), emulated_cpu_frequency);
+        return Common::Divide128On32(temporary, 1000000000).first;
     }
 
     void Pause([[maybe_unused]] bool is_paused) override {
@@ -58,8 +61,6 @@ public:
 
 private:
     base_time_point start_time;
-    const u64 emulated_clock_factor;
-    const u64 emulated_cpu_factor;
 };
 
 #ifdef ARCHITECTURE_x86_64