Common: Refactor & Document Wall clock.

src/common/uint128.cpp

@@ -6,12 +6,34 @@
 #include <intrin.h>
 
 #pragma intrinsic(_umul128)
+#pragma intrinsic(_udiv128)
 #endif
 #include <cstring>
 #include "common/uint128.h"
 
 namespace Common {
 
+#ifdef _MSC_VER
+
+u64 MultiplyAndDivide64(u64 a, u64 b, u64 d) {
+    u128 r{};
+    r[0] = _umul128(a, b, &r[1]);
+    u64 remainder;
+    return _udiv128(r[1], r[0], d, &remainder);
+}
+
+#else
+
+u64 MultiplyAndDivide64(u64 a, u64 b, u64 d) {
+    const u64 diva = a / d;
+    const u64 moda = a % d;
+    const u64 divb = b / d;
+    const u64 modb = b % d;
+    return diva * b + moda * divb + moda * modb / d;
+}
+
+#endif
+
 u128 Multiply64Into128(u64 a, u64 b) {
     u128 result;
 #ifdef _MSC_VER