From ba5c0a4579ece5d53c009a14d00e683e70b982f4 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Fri, 9 May 2025 18:29:52 +0100
Subject: Initial implementation

---
 tag.h | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 tag.h

(limited to 'tag.h')

diff --git a/tag.h b/tag.h
new file mode 100644
index 0000000..dab1fa0
--- /dev/null
+++ b/tag.h
@@ -0,0 +1,90 @@
+/* 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 GNU General Public License Version 2 for
+ * details.
+
+ * You may distribute and modify this code under the terms of the GNU General
+ * Public License Version 2, which you should have received a copy of along with
+ * this program.  If not, please go to <https://www.gnu.org/licenses/>.
+
+ * Created: 2025-04-06
+ * Description:
+ */
+
+#ifndef TAG_H
+#define TAG_H
+
+#include "./base.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+
+// Opaque structure to make tagged pointers a separate type from general
+// pointers
+typedef struct Obj lisp_t;
+
+enum Tag
+{
+  TAG_NIL  = 0b00000000, // Atomic types
+  TAG_INT  = 0b00000001, // special so we can encode 63 bit integers
+  TAG_SYM  = 0b00000100,
+  TAG_SSYM = 0b00001000,
+  TAG_CHAR = 0b00001100,
+  TAG_BOOL = 0b00010000,
+  // TAG_FLOAT = 0b00010100,
+  TAG_CONS = 0b00000010, // Container types
+  TAG_VEC  = 0b00000110,
+  TAG_STR  = 0b00001010,
+
+  NUM_TAGS = 9,
+};
+
+enum Shift
+{
+  SHIFT_INT   = 1,
+  SHIFT_SSYM  = 5,
+  SHIFT_CHAR  = 8,
+  SHIFT_SYM   = 8,
+  SHIFT_BOOL  = 8,
+  SHIFT_FLOAT = 8,
+
+  SHIFT_CONS = 8,
+  SHIFT_VEC  = 8,
+  SHIFT_STR  = 8,
+};
+
+enum Mask
+{
+  MASK_INT   = 0b00000001,
+  MASK_SSYM  = 0b00011111,
+  MASK_SYM   = 0b11111111,
+  MASK_CHAR  = 0b11111111,
+  MASK_BOOL  = 0b11111111,
+  MASK_FLOAT = 0b11111111,
+
+  MASK_CONS = 0b11111111,
+  MASK_VEC  = 0b11111111,
+  MASK_STR  = 0b11111111,
+};
+
+#define TAG(PTR, TYPE)    ((lisp_t *)(((PTR) << SHIFT_##TYPE) | TAG_##TYPE))
+#define IS_TAG(PTR, TYPE) (((u64)(PTR) & MASK_##TYPE) == TAG_##TYPE)
+#define UNTAG(PTR, TYPE)  (((u64)PTR) >> SHIFT_##TYPE)
+
+enum Tag tag_get(lisp_t *ptr);
+
+lisp_t *tag_int(i64 i);
+lisp_t *tag_char(u32 codepoint);
+lisp_t *tag_sym(void *ptr);
+lisp_t *tag_ssym(const char *data, size_t size);
+lisp_t *tag_bool(bool b);
+lisp_t *tag_vec(void *ptr);
+lisp_t *tag_str(void *ptr);
+lisp_t *tag_cons(void *ptr);
+
+#define INT_MAX ((1L << 62) - 1)
+#define INT_MIN (-(1L << 62))
+
+#endif
-- 
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