--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ater/out_frame.c	Mon Jun 24 09:20:54 2024 +0000
@@ -0,0 +1,147 @@
+/*
+ * Here we implement our TRAU-UL bit filling function.
+ *
+ * This code is based on trau_rtp_conv.c in libosmo-abis.
+ */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/crc8gen.h>
+#include <osmocom/trau/trau_frame.h>
+
+#include "out_frame.h"
+
+/* this corresponds to the bit-lengths of the individual codec
+ * parameters as indicated in Table 1.1 of TS 46.010 */
+static const uint8_t gsm_fr_map[] = {
+	6, 6, 5, 5, 4, 4, 3, 3,
+	7, 2, 2, 6, 3, 3, 3, 3,
+	3, 3, 3, 3, 3, 3, 3, 3,
+	3, 7, 2, 2, 6, 3, 3, 3,
+	3, 3, 3, 3, 3, 3, 3, 3,
+	3, 3, 7, 2, 2, 6, 3, 3,
+	3, 3, 3, 3, 3, 3, 3, 3,
+	3, 3, 3, 7, 2, 2, 6, 3,
+	3, 3, 3, 3, 3, 3, 3, 3,
+	3, 3, 3, 3
+};
+
+/*
+ * 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,
+};
+
+/* re-combine EFR parity bits */
+static inline void efr_parity_bits_1(ubit_t *check_bits, const ubit_t *d_bits)
+{
+	memcpy(check_bits + 0 , d_bits + 0, 22);
+	memcpy(check_bits + 22 , d_bits + 24, 3);
+	check_bits[25] = d_bits[28];
+}
+
+static inline void efr_parity_bits_2(ubit_t *check_bits, const ubit_t *d_bits)
+{
+	memcpy(check_bits + 0 , d_bits + 42, 10);
+	memcpy(check_bits + 10 , d_bits + 90, 2);
+}
+
+static inline void efr_parity_bits_3(ubit_t *check_bits, const ubit_t *d_bits)
+{
+	memcpy(check_bits + 0 , d_bits + 98, 5);
+	check_bits[5] = d_bits[104];
+	memcpy(check_bits + 6 , d_bits + 143, 2);
+}
+
+static inline void efr_parity_bits_4(ubit_t *check_bits, const ubit_t *d_bits)
+{
+	memcpy(check_bits + 0 , d_bits + 151, 10);
+	memcpy(check_bits + 10 , d_bits + 199, 2);
+}
+
+static inline void efr_parity_bits_5(ubit_t *check_bits, const ubit_t *d_bits)
+{
+	memcpy(check_bits + 0 , d_bits + 207, 5);
+	check_bits[5] = d_bits[213];
+	memcpy(check_bits + 6 , d_bits + 252, 2);
+}
+
+static void fill_data_fr(const uint8_t *data, struct osmo_trau_frame *tf)
+{
+	int i, j, k, l, o;
+
+	/* reassemble d-bits */
+	i = 0; /* counts bits */
+	j = 4; /* counts input bits */
+	k = gsm_fr_map[0]-1; /* current number bit in element */
+	l = 0; /* counts element bits */
+	o = 0; /* offset output bits */
+	while (i < 260) {
+		tf->d_bits[k+o] = (data[j/8] >> (7-(j%8))) & 1;
+		/* to avoid out-of-bounds access in gsm_fr_map[++l] */
+		if (i == 259)
+			break;
+		if (--k < 0) {
+			o += gsm_fr_map[l];
+			k = gsm_fr_map[++l]-1;
+		}
+		i++;
+		j++;
+	}
+}
+
+static void fill_data_efr(const uint8_t *data, struct osmo_trau_frame *tf)
+{
+	int i, j;
+	ubit_t check_bits[26];
+
+	/* reassemble d-bits */
+	tf->d_bits[0] = 1;
+	for (i = 1, j = 4; i < 39; i++, j++)
+		tf->d_bits[i] = (data[j/8] >> (7-(j%8))) & 1;
+	efr_parity_bits_1(check_bits, tf->d_bits);
+	osmo_crc8gen_set_bits(&gsm0860_efr_crc3, check_bits, 26,
+			tf->d_bits + 39);
+	for (i = 42, j = 42; i < 95; i++, j++)
+		tf->d_bits[i] = (data[j/8] >> (7-(j%8))) & 1;
+	efr_parity_bits_2(check_bits, tf->d_bits);
+	osmo_crc8gen_set_bits(&gsm0860_efr_crc3, check_bits, 12,
+			tf->d_bits + 95);
+	for (i = 98, j = 95; i < 148; i++, j++)
+		tf->d_bits[i] = (data[j/8] >> (7-(j%8))) & 1;
+	efr_parity_bits_3(check_bits, tf->d_bits);
+	osmo_crc8gen_set_bits(&gsm0860_efr_crc3, check_bits, 8,
+			tf->d_bits + 148);
+	for (i = 151, j = 145; i < 204; i++, j++)
+		tf->d_bits[i] = (data[j/8] >> (7-(j%8))) & 1;
+	efr_parity_bits_4(check_bits, tf->d_bits);
+	osmo_crc8gen_set_bits(&gsm0860_efr_crc3, check_bits, 12,
+			tf->d_bits + 204);
+	for (i = 207, j = 198; i < 257; i++, j++)
+		tf->d_bits[i] = (data[j/8] >> (7-(j%8))) & 1;
+	efr_parity_bits_5(check_bits, tf->d_bits);
+	osmo_crc8gen_set_bits(&gsm0860_efr_crc3, check_bits, 8,
+			tf->d_bits + 257);
+}
+
+void trau_frame_from_record(const uint8_t *rec, bool is_efr,
+			    struct osmo_trau_frame *tf)
+{
+	if (is_efr)
+		fill_data_efr(rec, tf);
+	else
+		fill_data_fr(rec, tf);
+	/* set BFI and SID flags */
+	tf->c_bits[11] = (rec[33] & 0x80) >> 7;
+	tf->c_bits[12] = (rec[33] & 0x02) >> 1;
+	tf->c_bits[13] = (rec[33] & 0x01) >> 0;
+}