From d10b2cc2a128c27517c2ad8cb98f975c2d3aa4bc Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Tue, 23 Jun 2026 10:40:13 +0200
Subject: [PATCH] Add atomic 128-bit compare-exchange function

---
 xtoskrnl/includes/rtl/atomic.hh |  3 +++
 xtoskrnl/rtl/atomic.cc          | 35 +++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/xtoskrnl/includes/rtl/atomic.hh b/xtoskrnl/includes/rtl/atomic.hh
index b98df71..08f74e6 100644
--- a/xtoskrnl/includes/rtl/atomic.hh
+++ b/xtoskrnl/includes/rtl/atomic.hh
@@ -52,6 +52,9 @@ namespace RTL
             STATIC XTFASTCALL LONG_PTR CompareExchange64(IN PLONG_PTR Address,
                                                       IN LONG_PTR Comperand,
                                                       IN LONG_PTR Exchange);
+            STATIC XTFASTCALL DOUBLE_ULONG_PTR CompareExchange128(IN PDOUBLE_ULONG_PTR Address,
+                                                                  IN DOUBLE_ULONG_PTR Comperand,
+                                                                  IN DOUBLE_ULONG_PTR Exchange);
             STATIC XTFASTCALL PVOID CompareExchangePointer(IN PVOID *Address,
                                                         IN PVOID Comperand,
                                                         IN PVOID Exchange);
diff --git a/xtoskrnl/rtl/atomic.cc b/xtoskrnl/rtl/atomic.cc
index cf8a28d..ab0a726 100644
--- a/xtoskrnl/rtl/atomic.cc
+++ b/xtoskrnl/rtl/atomic.cc
@@ -341,6 +341,41 @@ RTL::Atomic::CompareExchange64(IN PLONG_PTR Address,
     return __sync_val_compare_and_swap(Address, Comperand, Exchange);
 }
 
+/**
+ * Performs an atomic compare-exchange operation on the 64-bit or 128-bit value depending on architecture.
+ *
+ * @param Address
+ *        Supplies the address of the value to compare and potentially exchange.
+ *
+ * @param Comperand
+ *        Supplies the value to compare against.
+ *
+ * @param Exchange
+ *        Supplies the value to write if the comparison returns equality.
+ *
+ * @return This routine returns the original value at the given address.
+ *
+ * @since XT 1.0
+ */
+XTFASTCALL
+DOUBLE_ULONG_PTR
+RTL::Atomic::CompareExchange128(IN PDOUBLE_ULONG_PTR Address,
+                                IN DOUBLE_ULONG_PTR Comperand,
+                                IN DOUBLE_ULONG_PTR Exchange)
+{
+    DOUBLE_ULONG_PTR Value;
+
+    /* Make a local copy of the comperand */
+    Value = Comperand;
+
+    /* Perform an atomic compare-exchange operation */
+    __atomic_compare_exchange((VOLATILE PDOUBLE_ULONG_PTR)Address, &Value, &Exchange,
+                              FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
+
+    /* Return value */
+    return Value;
+}
+
 /**
  * Performs atomically compare exchange operation.
  *