--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/ietf_fo.c	Thu May 09 07:06:31 2024 +0000
@@ -0,0 +1,23 @@
+/*
+ * The function implemented in this module groks the first octet of
+ * an RFC 4867 payload and tells the calling application how many more
+ * bytes need to be read, or if the frame type is invalid.
+ */
+
+#include <stdint.h>
+#include "tw_amr.h"
+
+static const uint8_t extra_bytes_per_ft[9] =
+		{12, 13, 15, 17, 19, 20, 26, 31, 5};
+
+int amr_ietf_grok_first_octet(uint8_t fo)
+{
+	uint8_t ft;
+
+	ft = (fo & 0x78) >> 3;
+	if (ft == AMR_FT_NODATA)
+		return 0;
+	if (ft > MRDTX)
+		return -1;
+	return extra_bytes_per_ft[ft];
+}