/*
 * This program reads a 64 kbit/s timeslot recording file and looks for
 * TFO frames of GSM 08.62, specifically the FR/EFR kind.
 */

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>

static unsigned file_offset;

static enum {
	HUNT_FOR_0,
	HUNT_FOUND_0,
	GOT_8_ZEROS,
	SYNCED
} state;
static unsigned hunt_for_0_count, frame_pos_count;
static uint8_t in_frame_2bit[160], frame_bits[320], d_bits[260];

static void
unpack_dibits()
{
	int i, inb;
	uint8_t *op;

	op = frame_bits;
	for (i = 0; i < 160; i++) {
		inb = in_frame_2bit[i];
		if (inb & 1)
			*op++ = 1;
		else
			*op++ = 0;
		if (inb & 2)
			*op++ = 1;
		else
			*op++ = 0;
	}
}

static unsigned
bits_to_num(bits, nbits)
	uint8_t *bits;
	unsigned nbits;
{
	unsigned accum;
	unsigned n;

	accum = 0;
	for (n = 0; n < nbits; n++) {
		accum <<= 1;
		if (*bits)
			accum |= 1;
		bits++;
	}
	return accum;
}

static void
collect_d_bits()
{
	bcopy(frame_bits + 33, d_bits, 15);
	bcopy(frame_bits + 49, d_bits + 15, 15);
	bcopy(frame_bits + 65, d_bits + 30, 15);
	bcopy(frame_bits + 81, d_bits + 45, 15);
	bcopy(frame_bits + 97, d_bits + 60, 15);
	bcopy(frame_bits + 113, d_bits + 75, 15);
	bcopy(frame_bits + 129, d_bits + 90, 15);
	bcopy(frame_bits + 145, d_bits + 105, 15);
	bcopy(frame_bits + 161, d_bits + 120, 15);
	bcopy(frame_bits + 177, d_bits + 135, 15);
	bcopy(frame_bits + 193, d_bits + 150, 15);
	bcopy(frame_bits + 209, d_bits + 165, 15);
	bcopy(frame_bits + 225, d_bits + 180, 15);
	bcopy(frame_bits + 241, d_bits + 195, 15);
	bcopy(frame_bits + 257, d_bits + 210, 15);
	bcopy(frame_bits + 273, d_bits + 225, 15);
	bcopy(frame_bits + 289, d_bits + 240, 15);
	bcopy(frame_bits + 305, d_bits + 255, 5);
}

static void
process_frame()
{
	unsigned c1_5eq, c6_11;

	printf("Frame at 0x%x:\n", file_offset - 159);
	printf("  C1-C5: %u%u%u%u%u", frame_bits[17], frame_bits[18],
		frame_bits[19], frame_bits[20], frame_bits[21]);
	c1_5eq = bits_to_num(frame_bits + 17, 4) << 1;
	switch (c1_5eq) {
	case 0x02:
		fputs(" (FR UL)", stdout);
		break;
	case 0x1C:
		fputs(" (FR DL)", stdout);
		break;
	case 0x1A:
		fputs(" (EFR)", stdout);
		break;
	case 0x10:
		fputs(" (idle UL)", stdout);
		break;
	case 0x0E:
		fputs(" (idle DL)", stdout);
		break;
	}
	putchar('\n');
	c6_11 = bits_to_num(frame_bits + 22, 6);
	printf("  C6-C11: %u\n", c6_11);
	printf("  C12=%u C13=%u C14=%u C15=%u\n", frame_bits[28],
		frame_bits[29], frame_bits[30], frame_bits[31]);
	switch (c1_5eq) {
	case 0x02:
	case 0x1C:
		collect_d_bits();
		print_fr_frame(d_bits);
		break;
	case 0x1A:
		collect_d_bits();
		check_efr_crc(d_bits);
		print_efr_frame(d_bits);
		break;
	}
	printf("  C16=%u C17=%u C18=%u C19=%u C20=%u C21=%u\n",
		frame_bits[310], frame_bits[311], frame_bits[312],
		frame_bits[313], frame_bits[314], frame_bits[315]);
	printf("  T1=%u T2=%u T3=%u T4=%u\n", frame_bits[316], frame_bits[317],
		frame_bits[318], frame_bits[319]);
}

static int
check_sync_zeros()
{
	int i;

	for (i = 0; i < 16; i++) {
		if (frame_bits[i])
			return 0;
	}
	return 1;
}

static int
check_sync_ones_full()
{
	int i;

	for (i = 1; i < 20; i++) {
		if (!frame_bits[i*16])
			return 0;
	}
	return 1;
}

static int
check_sync_ones_partial()
{
	int i;

	for (i = 1; i < 20; i++) {
		if ((i & 1) == 0)
			continue;
		if (!frame_bits[i*16])
			return 0;
	}
	return 1;
}

static void
check_sync()
{
	if (check_sync_zeros() && check_sync_ones_partial()) {
		if (!check_sync_ones_full())
			printf("  Sync pattern partially overwritten!\n");
		return;
	}
	printf("Bad frame sync, returning to hunt state\n");
	state = HUNT_FOR_0;
}

static void
byte_input(inb)
{
	switch (state) {
	case HUNT_FOR_0:
		if (inb != 0)
			return;
		state = HUNT_FOUND_0;
		hunt_for_0_count = 1;
		return;
	case HUNT_FOUND_0:
		if (inb != 0) {
			state = HUNT_FOR_0;
			return;
		}
		hunt_for_0_count++;
		if (hunt_for_0_count >= 8)
			state = GOT_8_ZEROS;
		return;
	case GOT_8_ZEROS:
		if (inb & 1) {
			printf("Found frame sync at file offset 0x%x\n",
				file_offset - 8);
			bzero(in_frame_2bit, 8);
			in_frame_2bit[8] = inb;
			frame_pos_count = 9;
			state = SYNCED;
			return;
		}
		if (inb != 0)
			state = HUNT_FOR_0;
		return;
	case SYNCED:
		in_frame_2bit[frame_pos_count++] = inb;
		if (frame_pos_count < 160)
			return;
		frame_pos_count = 0;
		unpack_dibits();
		process_frame();
		check_sync();
		return;
	default:
		fprintf(stderr, "BUG: bad sync state\n");
		abort();
	}
}

main(argc, argv)
	char **argv;
{
	FILE *inf;
	int inb;

	if (argc != 2) {
		fprintf(stderr, "usage: %s binfile\n", argv[0]);
		exit(1);
	}
	inf = fopen(argv[1], "r");
	if (!inf) {
		perror(argv[1]);
		exit(1);
	}
	state = HUNT_FOR_0;
	for (file_offset = 0; ; file_offset++) {
		inb = getc(inf);
		if (inb < 0)
			break;
		inb &= 3;
		byte_input(inb);
	}
	exit(0);
}