src/vtx2ascii-src/vtxtools.c

   1 /*
   2  * vtxtools.c: Misceallaneous routines for VideoteXt (parity checking, handling of hexadecimal
   3  *             page-numbers)
   4  *
   5  * $Id: vtxtools.c,v 1.1 1996/10/14 21:36:23 mb Exp mb $
   6  *
   7  * Copyright (c) 1994-96 Martin Buck  <martin-2.buck@student.uni-ulm.de>
   8  * Read COPYING for more information
   9  *
  10  */
  11
  12 #include <sys/vtx.h>
  13 #include "misc.h"
  14 #include "vtxtools.h"
  15
  16
  17 static byte_t parity_table[256];
  18 static int init_done;
  19
  20
  21
  22 static void
  23 tools_init(void) {
  24   int pos, val, bit;
  25
  26   for (pos = 0; pos <= 255; pos++) {    /* Set up parity_table: If (parity_table[foo] & 0x80), */
  27     bit = 0;                            /* foo has odd number of bits set */
  28     val = pos;
  29     while (val) {               /* Count number of set bits in val; see K&R, Exercise 2-9 */
  30       bit ^= 0x80;
  31       val &= val - 1;
  32     }
  33     parity_table[pos] = bit | 0x7f;
  34   }
  35   /* parity_table is also used for hamming decoding: If (parity_table[foo] & 0x40), foo has
  36    * more than one bit-error and can't be corrected; otherwise the correct(ed) value is
  37    * parity_table[foo] & 0xf
  38    */
  39   for (pos = 0; pos <= 15; pos++) {
  40     val = ( !(pos & 1) ^ !!(pos & 4) ^ !!(pos & 8)) << 0 | !!(pos & 1) << 1 |
  41           ( !(pos & 1) ^ !!(pos & 2) ^ !!(pos & 8)) << 2 | !!(pos & 2) << 3 |
  42           ( !(pos & 1) ^ !!(pos & 2) ^ !!(pos & 4)) << 4 | !!(pos & 4) << 5 |
  43           (!!(pos & 2) ^ !!(pos & 4) ^ !!(pos & 8)) << 6 | !!(pos & 8) << 7;
  44     for (bit = 0; bit <= 8; bit++) {
  45       parity_table[val ^ ((1 << bit) & 0xff)] &= (0x80 | pos);
  46     }
  47   }
  48   init_done = TRUE;
  49 }
  50
  51
  52 /* Check parity of *val (parity bit is bit 7, odd parity)
  53  * Clear bit 7 of *val if parity OK & return TRUE, FALSE otherwise
  54  */
  55 int
  56 vtx_chkparity(byte_t *val) {
  57   if (!init_done)
  58     tools_init();
  59   if (parity_table[*val] & 0x80) {
  60     *val &= 0x7f;
  61     return TRUE;
  62   } else return FALSE;
  63 }
  64
  65
  66 /* Add odd parity bit to val
  67  */
  68 byte_t
  69 vtx_mkparity(byte_t val) {
  70   if (!init_done)
  71     tools_init();
  72   val &= 0x7f;
  73   return val | ((parity_table[val] & 0x80) ? 0 : 128);
  74 }
  75
  76
  77 /* Check hamming-encoding of val, return decoded value if OK, -1 otherwise
  78  */
  79 int
  80 vtx_chkhamming(byte_t val) {
  81   if (!init_done)
  82     tools_init();
  83   if (parity_table[val] & 0x40) {
  84     return -1;
  85   } else {
  86     return parity_table[val] & 0xf;
  87   }
  88 }
  89
  90
  91 /* Increase page-number. Skip over hexadecimal pages
  92  */
  93 int
  94 inc_vtxpage(int page) {
  95   page++;
  96   if ((page & 0xf) >= 0xa)
  97     page = (page & ~0xf) + 0x10;
  98   if ((page & 0xf0) >= 0xa0)
  99     page = (page & ~0xff) + 0x100;
 100   if (page >= 0x899)
 101     page = 0x100;
 102   return page;
 103 }
 104
 105
 106 /* Decrease page-number. Skip over hexadecimal pages
 107  */
 108 int
 109 dec_vtxpage(int page) {
 110   page--;
 111   if ((page & 0xf) >= 0xa)
 112     page = (page & ~0xf) + 9;
 113   if ((page & 0xf0) >= 0xa0)
 114     page = (page & ~0xff) + 0x99;
 115   if (page < 0x100)
 116     page = 0x899;
 117   return page;
 118 }
 119
 120
 121 int
 122 vtx_hex2dec(int pgnum) {
 123   return (pgnum / 0x100) * 100 + ((pgnum / 0x10) % 0x10) * 10 + (pgnum % 0x10);
 124 }
 125
 126
 127 int
 128 vtx_dec2hex(int pgnum) {
 129   return (pgnum / 100) * 0x100 + ((pgnum / 10) % 10) * 0x10 + (pgnum % 10);
 130 }
 131
 132
 133 int
 134 vtx_chkpgnum(int pgnum, int hex_ok) {
 135   if (hex_ok) {
 136     return (pgnum >= 0x100 && pgnum <= 0x8ff);
 137   } else {
 138     return (pgnum >= 0x100 && pgnum <= 0x899 && (pgnum & 0xff) <= 0x99 && (pgnum & 0xf) <= 9);
 139   }
 140 }