From e3253cddf9cb3a4a987775f8e20cbd4ffb46236e Mon Sep 17 00:00:00 2001
From: Thomas <thomas.giudici@proton.me>
Date: Fri, 16 Oct 2026 17:45:26 +0200
Subject: [PATCH] Fix undefined behavior in portable smulh

---
 src/instructions_portable.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/instructions_portable.cpp b/src/instructions_portable.cpp
index d7467271..5d5921fe 100644
--- a/src/instructions_portable.cpp
+++ b/src/instructions_portable.cpp
@@ -123,10 +123,10 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef HAVE_SMULH
 	int64_t smulh(int64_t a, int64_t b) {
-		int64_t hi = mulh(a, b);
+		uint64_t hi = mulh(a, b);
 		if (a < 0LL) hi -= b;
 		if (b < 0LL) hi -= a;
-		return hi;
+		return unsigned64ToSigned2sCompl(hi);
 	}
 	#define HAVE_SMULH
 #endif