core: Add token buffer

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

core/tokbuf.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause
+ */
+
+#include <sys/types.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <string.h>
+#include <errno.h>
+#include "cescal/tokbuf.h"
+
+int
+tokbuf_init(struct tokbuf *tokbuf)
+{
+    if (tokbuf == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    memset(tokbuf->buf, 0, sizeof(tokbuf->buf));
+    tokbuf->head = 0;
+    return 0;
+}
+
+int
+tokbuf_push(struct tokbuf *tokbuf, struct token *tok)
+{
+    if (tokbuf == NULL || tok == NULL) {
+        return -1;
+    }
+
+    if ((tokbuf->head++) >= TOKBUF_CAP) {
+        tokbuf->head = 0;
+    }
+
+    tokbuf->buf[tokbuf->head] = *tok;
+    return 0;
+}
+
+int
+tokbuf_noff(struct tokbuf *tokbuf, size_t noff, struct token *res)
+{
+    ssize_t off;
+
+    if (tokbuf == NULL || res == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (noff == 0) {
+        *res = tokbuf->buf[tokbuf->head + 1];
+        return 0;
+    }
+
+    if ((off = (tokbuf->head - noff + 1)) < 0) {
+        off = 0;
+    }
+
+    *res = tokbuf->buf[off];
+    return 0;
+}