/*
 * 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;
}