src/bitcomp.c

/*! \file bitcomp.c
 * Osmocom bit compression routines */
/*
 * (C) 2016 by sysmocom - s.f.m.c. GmbH
 * Author: Max Suraev <msuraev@sysmocom.de>
 *
 * 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.
 *
 */

/*! \defgroup bitcomp Bit compression
 *  @{
 * \file bitcomp.c */

#include <stdint.h>
#include <stdbool.h>
#include <errno.h>
#include <string.h>

#include <osmocom/core/bitvec.h>
#include <osmocom/core/bitcomp.h>

/*
 * Terminating codes for uninterrupted sequences of 0 and 1 up to 64 bit length
 * according to TS 44.060 9.1.10
 */
static const unsigned t4_term[2][64] = {
	{
		0b0000110111,
		0b10,
		0b11,
		0b010,
		0b011,
		0b0011,
		0b0010,
		0b00011,
		0b000101,
		0b000100,
		0b0000100,
		0b0000101,
		0b0000111,
		0b00000100,
		0b00000111,
		0b000011000,
		0b0000010111,
		0b0000011000,
		0b0000001000,
		0b00001100111,
		0b00001101000,
		0b00001101100,
		0b00000110111,
		0b00000101000,
		0b00000010111,
		0b00000011000,
		0b000011001010,
		0b000011001011,
		0b000011001100,
		0b000011001101,
		0b000001101000,
		0b000001101001,
		0b000001101010,
		0b000001101011,
		0b000011010010,
		0b000011010011,
		0b000011010100,
		0b000011010101,
		0b000011010110,
		0b000011010111,
		0b000001101100,
		0b000001101101,
		0b000011011010,
		0b000011011011,
		0b000001010100,
		0b000001010101,
		0b000001010110,
		0b000001010111,
		0b000001100100,
		0b000001100101,
		0b000001010010,
		0b000001010011,
		0b000000100100,
		0b000000110111,
		0b000000111000,
		0b000000100111,
		0b000000101000,
		0b000001011000,
		0b000001011001,
		0b000000101011,
		0b000000101100,
		0b000001011010,
		0b000001100110,
		0b000001100111
	},
	{
		0b00110101,
		0b000111,
		0b0111,
		0b1000,
		0b1011,
		0b1100,
		0b1110,
		0b1111,
		0b10011,
		0b10100,
		0b00111,
		0b01000,
		0b001000,
		0b000011,
		0b110100,
		0b110101,
		0b101010,
		0b101011,
		0b0100111,
		0b0001100,
		0b0001000,
		0b0010111,
		0b0000011,
		0b0000100,
		0b0101000,
		0b0101011,
		0b0010011,
		0b0100100,
		0b0011000,
		0b00000010,
		0b00000011,
		0b00011010,
		0b00011011,
		0b00010010,
		0b00010011,
		0b00010100,
		0b00010101,
		0b00010110,
		0b00010111,
		0b00101000,
		0b00101001,
		0b00101010,
		0b00101011,
		0b00101100,
		0b00101101,
		0b00000100,
		0b00000101,
		0b00001010,
		0b00001011,
		0b01010010,
		0b01010011,
		0b01010100,
		0b01010101,
		0b00100100,
		0b00100101,
		0b01011000,
		0b01011001,
		0b01011010,
		0b01011011,
		0b01001010,
		0b01001011,
		0b00110010,
		0b00110011,
		0b00110100
	}
};

static const unsigned t4_term_length[2][64] = {
	{10, 2, 2, 3, 3, 4, 4, 5, 6, 6, 7, 7, 7, 8, 8, 9, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12},
	{8, 6, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8}
};

static const unsigned t4_make_up_length[2][15] = {
	{10, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 13},
	{5, 5, 6, 7, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9}
};

static const unsigned t4_make_up[2][15] = {
	{
		0b0000001111,
		0b000011001000,
		0b000011001001,
		0b000001011011,
		0b000000110011,
		0b000000110100,
		0b000000110101,
		0b0000001101100,
		0b0000001101101,
		0b0000001001010,
		0b0000001001011,
		0b0000001001100,
		0b0000001001101,
		0b0000001110010,
		0b0000001110011
	},
	{
		0b11011,
		0b10010,
		0b010111,
		0b0110111,
		0b00110110,
		0b00110111,
		0b01100100,
		0b01100101,
		0b01101000,
		0b01100111,
		0b011001100,
		0b011001101,
		0b011010010,
		0b011010011,
		0b011010100
	 }
};

/*! Make-up codes for a given length
 *
 *  \return Return proper make-up code word for an uninterrupted
 *  sequence of b bits of length len according to modified ITU-T T.4
 *  from TS 44.060 Table 9.1.10.2 */
static inline int t4_rle(struct bitvec *bv, unsigned len, bool b)
{
	if (len >= 960) {
		bitvec_set_uint(bv, t4_make_up[b][14], t4_make_up_length[b][14]);
		return bitvec_set_uint(bv, t4_term[b][len - 960], t4_term_length[b][len - 960]);
	}

	if (len >= 896) {
		bitvec_set_uint(bv, t4_make_up[b][13], t4_make_up_length[b][13]);
		return bitvec_set_uint(bv, t4_term[b][len - 896], t4_term_length[b][len - 896]);
	}

	if (len >= 832) {
		bitvec_set_uint(bv, t4_make_up[b][12], t4_make_up_length[b][12]);
		return bitvec_set_uint(bv, t4_term[b][len - 832], t4_term_length[b][len - 832]);
	}

	if (len >= 768) {
		bitvec_set_uint(bv, t4_make_up[b][11], t4_make_up_length[b][11]);
		return bitvec_set_uint(bv, t4_term[b][len - 768], t4_term_length[b][len - 768]);
	}

	if (len >= 704) {
		bitvec_set_uint(bv, t4_make_up[b][10], t4_make_up_length[b][10]);
		return bitvec_set_uint(bv, t4_term[b][len - 704], t4_term_length[b][len - 704]);
	}

	if (len >= 640) {
		bitvec_set_uint(bv, t4_make_up[b][9], t4_make_up_length[b][9]);
		return bitvec_set_uint(bv, t4_term[b][len - 640], t4_term_length[b][len - 640]);
	}

	if (len >= 576) {
		bitvec_set_uint(bv, t4_make_up[b][8], t4_make_up_length[b][8]);
		return bitvec_set_uint(bv, t4_term[b][len - 576], t4_term_length[b][len - 576]);
	}

	if (len >= 512) {
		bitvec_set_uint(bv, t4_make_up[b][7], t4_make_up_length[b][7]);
		return bitvec_set_uint(bv, t4_term[b][len - 512], t4_term_length[b][len - 512]);
	}

	if (len >= 448) {
		bitvec_set_uint(bv, t4_make_up[b][6], t4_make_up_length[b][6]);
		return bitvec_set_uint(bv, t4_term[b][len - 448], t4_term_length[b][len - 448]);
	}

	if (len >= 384) {
		bitvec_set_uint(bv, t4_make_up[b][5], t4_make_up_length[b][5]);
		return bitvec_set_uint(bv, t4_term[b][len - 384], t4_term_length[b][len - 384]);
	}

	if (len >= 320) {
		bitvec_set_uint(bv, t4_make_up[b][4], t4_make_up_length[b][4]);
		return bitvec_set_uint(bv, t4_term[b][len - 320], t4_term_length[b][len - 320]);
	}

	if (len >= 256) {
		bitvec_set_uint(bv, t4_make_up[b][3], t4_make_up_length[b][3]);
		return bitvec_set_uint(bv, t4_term[b][len - 256], t4_term_length[b][len - 256]);
	}

	if (len >= 192) {
		bitvec_set_uint(bv, t4_make_up[b][2], t4_make_up_length[b][2]);
		return bitvec_set_uint(bv, t4_term[b][len - 192], t4_term_length[b][len - 192]);
	}

	if (len >= 128) {
		bitvec_set_uint(bv, t4_make_up[b][1], t4_make_up_length[b][1]);
		return bitvec_set_uint(bv, t4_term[b][len - 128], t4_term_length[b][len - 128]);
	}

	if (len >= 64) {
		bitvec_set_uint(bv, t4_make_up[b][0], t4_make_up_length[b][0]);
		return bitvec_set_uint(bv, t4_term[b][len - 64], t4_term_length[b][len - 64]);
	}

	return bitvec_set_uint(bv, t4_term[b][len], t4_term_length[b][len]);
}

/*! encode bit vector in-place using T4 encoding
 *  Assumes MSB first encoding.
 *  \param[in] bv bit vector to be encoded
 *  \return color code (if the encoding started with 0 or 1) or -1 on
 *  failure (encoded is bigger than original)
 */
int osmo_t4_encode(struct bitvec *bv)
{
	unsigned rl0 = bitvec_rl(bv, false), rl1 = bitvec_rl(bv, true);
	int r = (rl0 > rl1) ? 0 : 1;
	uint8_t orig[bv->data_len], tmp[bv->data_len * 2]; /* FIXME: better estimate max possible encoding overhead */
	struct bitvec comp, vec;
	comp.data = tmp;
	comp.data_len = bv->data_len * 2;
	bitvec_zero(&comp);
	vec.data = orig;
	vec.data_len = bv->data_len;
	bitvec_zero(&vec);
	memcpy(vec.data, bv->data, bv->data_len);
	vec.cur_bit = bv->cur_bit;

	while (vec.cur_bit > 0) {
		if (rl0 > rl1) {
			bitvec_shiftl(&vec, rl0);
			t4_rle(&comp, rl0, false);
		} else {
			bitvec_shiftl(&vec, rl1);
			t4_rle(&comp, rl1, true);
		}
		/*
		  TODO: implement backtracking for optimal encoding
		  printf(" -> [%d/%d]", comp.cur_bit + vec.cur_bit, bv->cur_bit);
		*/
		rl0 = bitvec_rl(&vec, false);
		rl1 = bitvec_rl(&vec, true);
	}
	if (comp.cur_bit < bv->cur_bit) {
		memcpy(bv->data, tmp, bv->data_len);
		bv->cur_bit = comp.cur_bit;
		return r;
	}
	return -1;
}

/*! @} */