core: Add token buffer

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

include/cescal/state.h

@@ -8,16 +8,19 @@
 
 #include <stdint.h>
 #include "cescal/readbuf.h"
+#include "cescal/tokbuf.h"
 
 /*
  * Compiler state machine
  *
- * @in_fd: Input file descriptor
- * @rb:    Read buffer
+ * @in_fd:  Input file descriptor
+ * @rb:     Read buffer
+ * @tokbuf: Token buffer
  */
 struct cescal_state {
     int in_fd;
     struct readbuf rb;
+    struct tokbuf tokbuf;
 };
 
 /*

include/cescal/tokbuf.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause
+ */
+
+#ifndef CESCAL_TOKBUF_H
+#define CESCAL_TOKBUF_H 1
+
+#include <stdint.h>
+#include <stddef.h>
+#include "cescal/token.h"
+
+#define TOKBUF_CAP 4
+
+struct tokbuf {
+    struct token buf[TOKBUF_CAP];
+    uint8_t head;
+};
+
+/*
+ * Initialize the token buffer
+ *
+ * @tokbuf:  Token buffer to initialize
+ *
+ * Returns zero on success
+ */
+int tokbuf_init(struct tokbuf *tokbuf);
+
+/*
+ * Push a token onto the token buffer
+ *
+ * @tokbuf: Token buffer to push to
+ * @tok:    Token to push
+ *
+ * Returns zero on success
+ */
+int tokbuf_push(struct tokbuf *tokbuf, struct token *tok);
+
+/*
+ * Peek at the token buffer from a negative offset backwards
+ *
+ * @tokbuf: Token buffer to read from
+ * @noff:   Negative offset
+ * @res:    Result is written here
+ *
+ * Returns zero on success
+ */
+int tokbuf_noff(struct tokbuf *tokbuf, size_t noff, struct token *res);
+
+#endif  /* !CESCAL_TOKBUF_H */