From 7512485b9440b742b38da451aaca4a72369596ec Mon Sep 17 00:00:00 2001
From: X512 <danger_mail@list.ru>
Date: Sun, 26 Jan 2020 14:48:30 +0100
Subject: [PATCH] Optimize system_time function

The uint128 code does not optimize as well as expected. Since this
function can be called quite often, use a more optimal implementation
(quite similar to what we had for x86_64 before refactoring).

Unfortunately this is still not as good as the hand-optimized assembler
previously used for 32bit x86, unless compiled with clang, where it gets
pretty close.
---
 src/system/boot/arch/x86/cpu.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/system/boot/arch/x86/cpu.cpp b/src/system/boot/arch/x86/cpu.cpp
index 9843a6cf76..9389fe042b 100644
--- a/src/system/boot/arch/x86/cpu.cpp
+++ b/src/system/boot/arch/x86/cpu.cpp
@@ -304,8 +304,10 @@ slower_sample:
 extern "C" bigtime_t
 system_time()
 {
-	uint128 tsc(rdtsc());
-	return uint64((tsc * gTimeConversionFactor) >> 32);
+	uint64 tsc = rdtsc();
+	uint64 lo = (uint32)tsc;
+	uint64 hi = tsc >> 32;
+	return ((lo * gTimeConversionFactor) >> 32) + hi * gTimeConversionFactor;
 }