usr.sbin/vidcontrol/decode.c

   1 /*-
   2  * Copyright (c) 1994 Søren Schmidt
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer,
  10  *    in this position and unchanged.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. The name of the author may not be used to endorse or promote products
  15  *    derived from this software withough specific prior written permission
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef lint
  30 static const char rcsid[] =
  31   "$FreeBSD: src/usr.sbin/vidcontrol/decode.c,v 1.8.2.1 2001/05/28 17:36:56 sobomax Exp $";
  32 #endif /* not lint */
  33
  34 #include <stdio.h>
  35 #include <string.h>
  36 #include "decode.h"
  37
  38 int decode(FILE *fd, char *buffer, int len)
  39 {
  40         int n, pos = 0, tpos;
  41         char *bp, *p;
  42         char tbuffer[3];
  43         char temp[128];
  44
  45 #define DEC(c)  (((c) - ' ') & 0x3f)
  46
  47         do {
  48                 if (!fgets(temp, sizeof(temp), fd))
  49                         return(0);
  50         } while (strncmp(temp, "begin ", 6));
  51         sscanf(temp, "begin %o %s", &n, temp);
  52         bp = buffer;
  53         for (;;) {
  54                 if (!fgets(p = temp, sizeof(temp), fd))
  55                         return(0);
  56                 if ((n = DEC(*p)) <= 0)
  57                         break;
  58                 for (++p; n > 0; p += 4, n -= 3) {
  59                         tpos = 0;
  60                         if (n >= 3) {
  61                                 tbuffer[tpos++] = DEC(p[0])<<2 | DEC(p[1])>>4;
  62                                 tbuffer[tpos++] = DEC(p[1])<<4 | DEC(p[2])>>2;
  63                                 tbuffer[tpos++] = DEC(p[2])<<6 | DEC(p[3]);
  64                         }
  65                         else {
  66                                 if (n >= 1) {
  67                                         tbuffer[tpos++] =
  68                                                 DEC(p[0])<<2 | DEC(p[1])>>4;
  69                                 }
  70                                 if (n >= 2) {
  71                                         tbuffer[tpos++] =
  72                                                 DEC(p[1])<<4 | DEC(p[2])>>2;
  73                                 }
  74                                 if (n >= 3) {
  75                                         tbuffer[tpos++] =
  76                                                 DEC(p[2])<<6 | DEC(p[3]);
  77                                 }
  78                         }
  79                         if (tpos == 0)
  80                                 continue;
  81                         if (tpos + pos > len) {
  82                                 tpos = len - pos;
  83                                 /*
  84                                  * Arrange return value > len to indicate
  85                                  * overflow.
  86                                  */
  87                                 pos++;
  88                         }
  89                         bcopy(tbuffer, bp, tpos);
  90                         pos += tpos;
  91                         bp += tpos;
  92                         if (pos > len)
  93                                 return(pos);
  94                 }
  95         }
  96         if (!fgets(temp, sizeof(temp), fd) || strcmp(temp, "end\n"))
  97                 return(0);
  98         return(pos);
  99 }