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
ham84_(integer * input,integer * output,integer * errcnt)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
100