1 files changed, 76 insertions, 0 deletions
diff --git a/impl/tag.c b/impl/tag.c
new file mode 100644
index 0000000..e6396cc
--- /dev/null
+++ b/impl/tag.c
@@ -0,0 +1,76 @@
+/* Copyright (C) 2025 Aryadev Chavali
+
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the Unlicense for details.
+
+ * You may distribute and modify this code under the terms of the Unlicense,
+ * which you should have received a copy of along with this program.  If not,
+ * please go to <https://unlicense.org/>.
+
+ * Created: 2025-08-19
+ * Description: Pointer tagging
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include <alisp.h>
+
+lisp_t *tag_int(i64 i)
+{
+  return TAG((u64)i, INT);
+}
+
+lisp_t *tag_sym(char *str)
+{
+  return TAG((u64)str, SYM);
+}
+
+lisp_t *tag_vec(vec_t *vec)
+{
+  return TAG((u64)vec, VEC);
+}
+
+lisp_t *tag_cons(cons_t *cons)
+{
+  return TAG((u64)cons, CONS);
+}
+
+tag_t get_tag(lisp_t *lisp)
+{
+  static_assert(NUM_TAGS == 5);
+  if (!lisp)
+    return TAG_NIL;
+  else if (IS_TAG(lisp, INT))
+    return TAG_INT;
+
+  return (u64)lisp & 0xFF;
+}
+
+i64 as_int(lisp_t *obj)
+{
+  assert(IS_TAG(obj, INT));
+  u64 p_obj = (u64)obj;
+  return UNTAG(p_obj, INT) |               // Delete the tag
+         (NTH_BYTE(p_obj, 7) & 0x80) << 56 // duplicate the MSB (preserve sign)
+      ;
+}
+
+char *as_sym(lisp_t *obj)
+{
+  assert(IS_TAG(obj, SYM));
+  return (char *)UNTAG(obj, SYM);
+}
+
+cons_t *as_cons(lisp_t *obj)
+{
+  assert(IS_TAG(obj, CONS));
+  return (cons_t *)UNTAG(obj, CONS);
+}
+
+vec_t *as_vec(lisp_t *obj)
+{
+  assert(IS_TAG(obj, VEC));
+  return (vec_t *)UNTAG(obj, VEC);
+}