tptr: add pointer tagging templates (#7067)

src/util/tptr.h

@@ -21,6 +21,7 @@ Revision History:
 
 #include <cstdint>
 #include "util/machine.h"
+#include "util/debug.h"
 
 #define TAG_SHIFT        PTR_ALIGNMENT
 #define ALIGNMENT_VALUE  (1 << PTR_ALIGNMENT)
@@ -42,4 +43,22 @@ Revision History:
 
 #define UNBOXINT(PTR) static_cast<int>(reinterpret_cast<uintptr_t>(PTR) >> PTR_ALIGNMENT)
 
-
+template <typename U, typename T>
+U unbox(T* ptr) {
+    return static_cast<U>(reinterpret_cast<std::uintptr_t>(ptr) >> PTR_ALIGNMENT);
+}
+
+template <typename T>
+unsigned get_tag(T* ptr) {
+    return reinterpret_cast<std::uintptr_t>(ptr) & TAG_MASK;
+}
+
+template <typename T, typename U>
+T* box(U val, std::uintptr_t tag = 0) {
+    static_assert( sizeof(T*) >= sizeof(U) + PTR_ALIGNMENT );
+    SASSERT_EQ(tag & PTR_MASK, 0);
+    T* ptr = reinterpret_cast<T*>((static_cast<std::uintptr_t>(val) << PTR_ALIGNMENT) | tag);
+    SASSERT_EQ(val, unbox<U>(ptr));  // roundtrip of conversion integer -> pointer -> integer is not actually guaranteed by the C++ standard (but seems fine in practice, as indicated by previous usage of BOXINT/UNBOXINT)
+    SASSERT_EQ(tag, get_tag(ptr));
+    return ptr;
+}