Pointer tagging!

Copied from oats, just the basics required for tagging integers or
symbols.

1 files changed, 42 insertions, 0 deletions

diff --git a/tag.c b/tag.c
new file mode 100644
index 0000000..7688d63
--- /dev/null
+++ b/tag.c
@@ -0,0 +1,42 @@
+/* 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 "./base.h"
+
+lisp_t *tag_int(i64 i)
+{
+  return TAG((u64)i, INT);
+}
+
+lisp_t *tag_sym(char *str)
+{
+  return TAG((u64)str, SYM);
+}
+
+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);
+}