lpc10/ham84.c

   1 /*
   2
   3  * Revision 1.1  1996/08/19  22:32:07  jaf
   4  * Initial revision
   5  *
   6
   7 */
   8
   9 /*  -- translated by f2c (version 19951025).
  10    You must link the resulting object file with the libraries:
  11         -lf2c -lm   (in that order)
  12 */
  13
  14 #include "f2c.h"
  15
  16 extern int ham84_(integer *input, integer *output, integer *errcnt);
  17
  18 /* ***************************************************************** */
  19
  20 /*      HAM84 Version 45G */
  21
  22 /*
  23  * Revision 1.1  1996/08/19  22:32:07  jaf
  24  * Initial revision
  25  * */
  26 /* Revision 1.3  1996/03/21  15:26:00  jaf */
  27 /* Put comment header in standard form. */
  28
  29 /* Revision 1.2  1996/03/13  22:00:13  jaf */
  30 /* Comments added explaining that none of the local variables of this */
  31 /* subroutine need to be saved from one invocation to the next. */
  32
  33 /* Revision 1.1  1996/02/07 14:47:04  jaf */
  34 /* Initial revision */
  35
  36
  37 /* ***************************************************************** */
  38
  39 /*  Hamming 8,4 Decoder - can correct 1 out of seven bits */
  40 /*   and can detect up to two errors. */
  41
  42 /* Input: */
  43 /*  INPUT  - Seven bit data word, 4 bits parameter and */
  44 /*           4 bits parity information */
  45 /* Input/Output: */
  46 /*  ERRCNT - Sums errors detected by Hamming code */
  47 /* Output: */
  48 /*  OUTPUT - 4 corrected parameter bits */
  49
  50 /* This subroutine is entered with an eight bit word in INPUT.  The 8th */
  51 /* bit is parity and is stripped off.  The remaining 7 bits address the */
  52 /* hamming 8,4 table and the output OUTPUT from the table gives the 4 */
  53 /* bits of corrected data.  If bit 4 is set, no error was detected. */
  54 /* ERRCNT is the number of errors counted. */
  55
  56 /* This subroutine has no local state. */
  57
  58 /* Subroutine */ int ham84_(integer *input, integer *output, integer *errcnt)
  59 {
  60     /* Initialized data */
  61
  62     static integer dactab[128] = { 16,0,0,3,0,5,14,7,0,9,14,11,14,13,30,14,0,
  63             9,2,7,4,7,7,23,9,25,10,9,12,9,14,7,0,5,2,11,5,21,6,5,8,11,11,27,
  64             12,5,14,11,2,1,18,2,12,5,2,7,12,9,2,11,28,12,12,15,0,3,3,19,4,13,
  65             6,3,8,13,10,3,13,29,14,13,4,1,10,3,20,4,4,7,10,9,26,10,4,13,10,15,
  66             8,1,6,3,6,5,22,6,24,8,8,11,8,13,6,15,1,17,2,1,4,1,6,15,8,1,10,15,
  67             12,15,15,31 };
  68
  69     integer i__, j, parity;
  70
  71 /*       Arguments */
  72 /*       Parameters/constants */
  73 /*       Local variables that need not be saved */
  74 /*  Determine parity of input word */
  75     parity = *input & 255;
  76     parity ^= parity / 16;
  77     parity ^= parity / 4;
  78     parity ^= parity / 2;
  79     parity &= 1;
  80     i__ = dactab[*input & 127];
  81     *output = i__ & 15;
  82     j = i__ & 16;
  83     if (j != 0) {
  84 /*          No errors detected in seven bits */
  85         if (parity != 0) {
  86             ++(*errcnt);
  87         }
  88     } else {
  89 /*          One or two errors detected */
  90         ++(*errcnt);
  91         if (parity == 0) {
  92 /*             Two errors detected */
  93             ++(*errcnt);
  94             *output = -1;
  95         }
  96     }
  97     return 0;
  98 } /* ham84_ */
  99