firmware/libcommon/source/iso7816_fidi.c

/* ISO7816-3 Fi/Di tables + computation */
/* (C) 2010-2015 by Harald Welte <hwelte@hmw-consulting.de>
 *
 *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

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

#include "utils.h"
#include "iso7816_fidi.h"

/* Table 7 of ISO 7816-3:2006 */
static const uint16_t fi_table[] = {
	372, 372, 558, 744, 1116, 1488, 1860, 0,
	0, 512, 768, 1024, 1536, 2048, 0, 0
};

/* Table 8 from ISO 7816-3:2006 */
static const uint8_t di_table[] = {
	0, 1, 2, 4, 8, 16, 32, 64,
	12, 20, 2, 4, 8, 16, 32, 64,
};

/* compute the F/D ratio based on Fi and Di values */
int compute_fidi_ratio(uint8_t fi, uint8_t di)
{
	uint16_t f, d;
	int ret;

	if (fi >= ARRAY_SIZE(fi_table) ||
	    di >= ARRAY_SIZE(di_table))
		return -EINVAL;

	f = fi_table[fi];
	if (f == 0)
		return -EINVAL;

	d = di_table[di];
	if (d == 0)
		return -EINVAL;

	/* See table 7 of ISO 7816-3: From 1000 on we divide by 1/d,
	 * which equals a multiplication by d */
	if (di < 8)
		ret = f / d;
	else
		ret = f * d;

	return ret;
}