spkg: strlib: Add RtlMemCmp() to string lib

Signed-off-by: Chloe M. <chloe@yiffware.org>

service/spkg/head/string.h

@@ -18,4 +18,15 @@
  */
 USIZE RtlStrLen(const CHAR *String);
 
+/*
+ * Compare the differences between two strings
+ *
+ * @Buffer1: First buffer to compare
+ * @Buffer2: Second buffer to compare
+ * @Length:  Number of bytes to compare
+ *
+ * Returns the differences
+ */
+LONG RtlMemCmp(const VOID *Buffer1, const VOID *Buffer2, USIZE Length);
+
 #endif  /* !_SPKG_STRING_H_ */

service/spkg/strlib/memcmp.c

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: RtlMemCmp() implementation
+ * Author:      Chloe M.
+ */
+
+#include <string.h>
+
+LONG
+RtlMemCmp(const VOID *Buffer1, const VOID *Buffer2, USIZE Length)
+{
+    const UCHAR *Ptr1 = Buffer1;
+    const UCHAR *Ptr2 = Buffer2;
+
+    if (Buffer1 == NULL || Buffer2 == NULL) {
+        return 0;
+    }
+
+    if (Length == 0) {
+        return 0;
+    }
+
+    do {
+        if (*Ptr1++ != *Ptr2++) {
+            return (*--Ptr1 - *--Ptr2);
+        }
+    } while (--Length != 0);
+
+    return 0;
+}