--- a/libutil/Makefile	Fri Mar 17 14:31:54 2023 -0800
+++ b/libutil/Makefile	Fri Mar 17 16:52:21 2023 -0800
@@ -1,7 +1,7 @@
 CC=	gcc
 CFLAGS=	-O2
-OBJS=	dtmf_valid.o extdigits.o imsi_entry.o mncc_debug.o mncc_utils.o \
-	nanp_valid.o numstring.o sockinit.o
+OBJS=	bitfunc.o crc8gen.o dtmf_valid.o extdigits.o imsi_entry.o mncc_debug.o \
+	mncc_utils.o nanp_valid.o numstring.o sockinit.o tfo_msg_enc.o
 LIB=	libutil.a
 
 all:	${LIB}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libutil/bitfunc.c	Fri Mar 17 16:52:21 2023 -0800
@@ -0,0 +1,14 @@
+/*
+ * Some bit manipulation functions.
+ */
+
+#include <stdint.h>
+#include "osmo_bits.h"
+
+void uint16_to_bits(uint16_t word, ubit_t *out, unsigned nbits)
+{
+	unsigned n;
+
+	for (n = 0; n < nbits; n++)
+		out[n] = (word >> (nbits-n-1)) & 1;
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libutil/crc8gen.c	Fri Mar 17 16:52:21 2023 -0800
@@ -0,0 +1,115 @@
+/*! \file crc8gen.c
+ * Osmocom generic CRC routines (for max 8 bits poly). */
+/*
+ * Copyright (C) 2011  Sylvain Munaut <tnt@246tNt.com>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/*! \addtogroup crc
+ *  @{
+ *  Osmocom generic CRC routines (for max 8 bits poly).
+ *
+ *  \file crc8gen.c.tpl */
+
+#include <stdint.h>
+#include "osmo_bits.h"
+
+/*! Compute the CRC value of a given array of hard-bits
+ *  \param[in] code The CRC code description to apply
+ *  \param[in] in Array of hard bits
+ *  \param[in] len Length of the array of hard bits
+ *  \returns The CRC value
+ */
+uint8_t
+osmo_crc8gen_compute_bits(const struct osmo_crc8gen_code *code,
+                           const ubit_t *in, int len)
+{
+	const uint8_t poly = code->poly;
+	uint8_t crc = code->init;
+	int i, n = code->bits-1;
+
+	for (i=0; i<len; i++) {
+		uint8_t bit = in[i] & 1;
+		crc ^= (bit << n);
+		if (crc & ((uint8_t)1 << n)) {
+			crc <<= 1;
+			crc ^= poly;
+		} else {
+			crc <<= 1;
+		}
+		crc &= ((uint8_t)1 << code->bits) - 1;
+	}
+
+	crc ^= code->remainder;
+
+	return crc;
+}
+
+
+/*! Checks the CRC value of a given array of hard-bits
+ *  \param[in] code The CRC code description to apply
+ *  \param[in] in Array of hard bits
+ *  \param[in] len Length of the array of hard bits
+ *  \param[in] crc_bits Array of hard bits with the alleged CRC
+ *  \returns 0 if CRC matches. 1 in case of error.
+ *
+ * The crc_bits array must have a length of code->len
+ */
+int
+osmo_crc8gen_check_bits(const struct osmo_crc8gen_code *code,
+                         const ubit_t *in, int len, const ubit_t *crc_bits)
+{
+	uint8_t crc;
+	int i;
+
+	crc = osmo_crc8gen_compute_bits(code, in, len);
+
+	for (i=0; i<code->bits; i++)
+		if (crc_bits[i] ^ ((crc >> (code->bits-i-1)) & 1))
+			return 1;
+
+	return 0;
+}
+
+
+/*! Computes and writes the CRC value of a given array of bits
+ *  \param[in] code The CRC code description to apply
+ *  \param[in] in Array of hard bits
+ *  \param[in] len Length of the array of hard bits
+ *  \param[in] crc_bits Array of hard bits to write the computed CRC to
+ *
+ * The crc_bits array must have a length of code->len
+ */
+void
+osmo_crc8gen_set_bits(const struct osmo_crc8gen_code *code,
+                       const ubit_t *in, int len, ubit_t *crc_bits)
+{
+	uint8_t crc;
+	int i;
+
+	crc = osmo_crc8gen_compute_bits(code, in, len);
+
+	for (i=0; i<code->bits; i++)
+		crc_bits[i] = ((crc >> (code->bits-i-1)) & 1);
+}
+
+/*! @} */
+
+/* vim: set syntax=c: */

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libutil/osmo_bits.h	Fri Mar 17 16:52:21 2023 -0800
@@ -0,0 +1,35 @@
+/*
+ * This include file has been put together from Osmocom (specifically
+ * libosmocore) header files, containing definitions for bit vector
+ * manipulation and CRC functions.
+ */
+
+/* from bits.h */
+
+/*! unpacked bit (0 or 1): 1 bit per byte */
+typedef uint8_t ubit_t;
+
+/* from crc8gen.h */
+
+/*! structure describing a given CRC code of max 8 bits */
+struct osmo_crc8gen_code {
+	int bits;          /*!< Actual number of bits of the CRC */
+	uint8_t poly;      /*!< Polynom (normal representation, MSB omitted */
+	uint8_t init;      /*!< Initialization value of the CRC state */
+	uint8_t remainder; /*!< Remainder of the CRC (final XOR) */
+};
+
+uint8_t osmo_crc8gen_compute_bits(const struct osmo_crc8gen_code *code,
+                                  const ubit_t *in, int len);
+int osmo_crc8gen_check_bits(const struct osmo_crc8gen_code *code,
+                            const ubit_t *in, int len, const ubit_t *crc_bits);
+void osmo_crc8gen_set_bits(const struct osmo_crc8gen_code *code,
+                           const ubit_t *in, int len, ubit_t *crc_bits);
+
+/*
+ * Themyscira-added (not Osmocom-originating) functions
+ * that use the ubit_t defined type that (to our knowledge)
+ * was invented by Osmocom.
+ */
+
+void uint16_to_bits(uint16_t word, ubit_t *out, unsigned nbits);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libutil/tfo_msg_enc.c	Fri Mar 17 16:52:21 2023 -0800
@@ -0,0 +1,33 @@
+/*
+ * The function implemented in this module encodes a GSM 08.62 Extension_Block.
+ */
+
+#include <stdint.h>
+#include "osmo_bits.h"
+
+/*
+ * EFR TRAU parity
+ *
+ * g(x) = x^3 + x^1 + 1
+ */
+static const struct osmo_crc8gen_code gsm0860_efr_crc3 = {
+	.bits = 3,
+	.poly = 0x3,
+	.init = 0x0,
+	.remainder = 0x7,
+};
+
+void
+encode_tfo_ext_words(bits_2_10, bits_12_15, ex, out)
+	unsigned bits_2_10, bits_12_15, ex;
+	uint16_t *out;
+{
+	ubit_t crc_in[13];
+	uint8_t crc;
+
+	uint16_to_bits(bits_2_10, crc_in, 9);
+	uint16_to_bits(bits_12_15, crc_in + 9, 4);
+	crc = osmo_crc8gen_compute_bits(&gsm0860_efr_crc3, crc_in, 13);
+	out[0] = bits_2_10;
+	out[1] = (bits_12_15 << 5) | (crc << 2) | ex;
+}