From b7fea22c7d5716f0f1b6094504f3bc9d9b84b553 Mon Sep 17 00:00:00 2001
From: offtkp <parisoplop@gmail.com>
Date: Mon, 2 Sep 2024 02:35:13 +0300
Subject: [PATCH] Set CF correctly on BLSMSK patch

---
 src/core/cpu_patches.cpp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/core/cpu_patches.cpp b/src/core/cpu_patches.cpp
index 5021616c5..a7624e303 100644
--- a/src/core/cpu_patches.cpp
+++ b/src/core/cpu_patches.cpp
@@ -323,9 +323,26 @@ static void GenerateBLSMSK(const ZydisDecodedOperand* operands, Xbyak::CodeGener
 
     SaveRegisters(c, {scratch});
 
+    Xbyak::Label set_carry, clear_carry, end;
+
+    // BLSMSK sets CF to zero if source is NOT zero, otherwise it sets CF to one.
     c.mov(scratch, *src);
+    c.test(scratch, scratch);
+    c.jz(set_carry);
+    c.jmp(clear_carry);
+
+    c.L(set_carry);
     c.dec(scratch);
     c.xor_(scratch, *src);
+    c.stc();
+    c.jmp(end);
+
+    c.L(clear_carry);
+    c.dec(scratch);
+    c.xor_(scratch, *src);
+    // We don't need to clear carry here since XOR does that for us
+
+    c.L(end);
     c.mov(dst, scratch);
 
     RestoreRegisters(c, {scratch});