usr.sbin/vidcontrol/decode.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1994 Søren 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
  32 static const char rcsid[] =
  33   "$FreeBSD$";
  34 #endif /* not lint */
  35
  36 #include <stdio.h>
  37 #include <string.h>
  38 #include "decode.h"
  39
  40 int 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 }