/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1994 Søren Schmidt
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer,
 *    in this position and unchanged.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef lint
static const char rcsid[] =
  "$FreeBSD$";
#endif /* not lint */

#include <stdio.h>
#include <string.h>
#include "decode.h"

int decode(FILE *fd, char *buffer, int len)
{
	int n, pos = 0, tpos;
	char *bp, *p;
	char tbuffer[3];
	char temp[128];

#define	DEC(c)	(((c) - ' ') & 0x3f)

	do {
		if (!fgets(temp, sizeof(temp), fd))
			return(0);
	} while (strncmp(temp, "begin ", 6));
	sscanf(temp, "begin %o %s", (unsigned *)&n, temp);
	bp = buffer;
	for (;;) {
		if (!fgets(p = temp, sizeof(temp), fd))
			return(0);
		if ((n = DEC(*p)) <= 0)
			break;
		for (++p; n > 0; p += 4, n -= 3) {
			tpos = 0;
			if (n >= 3) {
				tbuffer[tpos++] = DEC(p[0])<<2 | DEC(p[1])>>4;
				tbuffer[tpos++] = DEC(p[1])<<4 | DEC(p[2])>>2;
				tbuffer[tpos++] = DEC(p[2])<<6 | DEC(p[3]);
			}
			else {
				if (n >= 1) {
					tbuffer[tpos++] =
						DEC(p[0])<<2 | DEC(p[1])>>4;
				}
				if (n >= 2) {
					tbuffer[tpos++] =
						DEC(p[1])<<4 | DEC(p[2])>>2;
				}
				if (n >= 3) {
					tbuffer[tpos++] =
						DEC(p[2])<<6 | DEC(p[3]);
				}
			}
			if (tpos == 0)
				continue;
			if (tpos + pos > len) {
				tpos = len - pos;
				/*
				 * Arrange return value > len to indicate
				 * overflow.
				 */
				pos++;
			}
			bcopy(tbuffer, bp, tpos);
			pos += tpos;
			bp += tpos;
			if (pos > len)
				return(pos);
		}
	}
	if (!fgets(temp, sizeof(temp), fd) || strcmp(temp, "end\n"))
		return(0);
	return(pos);
}