1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1994 S��ren Schmidt
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer,
12 *    in this position and unchanged.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. The name of the author may not be used to endorse or promote products
17 *    derived from this software without specific prior written permission
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
20 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
21 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
22 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
23 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
24 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
28 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31#ifndef lint
32static const char rcsid[] =
33  "$FreeBSD: stable/11/usr.sbin/vidcontrol/decode.c 330449 2018-03-05 07:26:05Z eadler $";
34#endif /* not lint */
35
36#include <stdio.h>
37#include <string.h>
38#include "decode.h"
39
40int decode(FILE *fd, char *buffer, int len)
41{
42	int n, pos = 0, tpos;
43	char *bp, *p;
44	char tbuffer[3];
45	char temp[128];
46
47#define	DEC(c)	(((c) - ' ') & 0x3f)
48
49	do {
50		if (!fgets(temp, sizeof(temp), fd))
51			return(0);
52	} while (strncmp(temp, "begin ", 6));
53	sscanf(temp, "begin %o %s", (unsigned *)&n, temp);
54	bp = buffer;
55	for (;;) {
56		if (!fgets(p = temp, sizeof(temp), fd))
57			return(0);
58		if ((n = DEC(*p)) <= 0)
59			break;
60		for (++p; n > 0; p += 4, n -= 3) {
61			tpos = 0;
62			if (n >= 3) {
63				tbuffer[tpos++] = DEC(p[0])<<2 | DEC(p[1])>>4;
64				tbuffer[tpos++] = DEC(p[1])<<4 | DEC(p[2])>>2;
65				tbuffer[tpos++] = DEC(p[2])<<6 | DEC(p[3]);
66			}
67			else {
68				if (n >= 1) {
69					tbuffer[tpos++] =
70						DEC(p[0])<<2 | DEC(p[1])>>4;
71				}
72				if (n >= 2) {
73					tbuffer[tpos++] =
74						DEC(p[1])<<4 | DEC(p[2])>>2;
75				}
76				if (n >= 3) {
77					tbuffer[tpos++] =
78						DEC(p[2])<<6 | DEC(p[3]);
79				}
80			}
81			if (tpos == 0)
82				continue;
83			if (tpos + pos > len) {
84				tpos = len - pos;
85				/*
86				 * Arrange return value > len to indicate
87				 * overflow.
88				 */
89				pos++;
90			}
91			bcopy(tbuffer, bp, tpos);
92			pos += tpos;
93			bp += tpos;
94			if (pos > len)
95				return(pos);
96		}
97	}
98	if (!fgets(temp, sizeof(temp), fd) || strcmp(temp, "end\n"))
99		return(0);
100	return(pos);
101}
102