1 //
2 // fec_example.c
3 //
4 // This example demonstrates the interface for forward error-
5 // correction (FEC) codes. A buffer of data bytes is encoded and
6 // corrupted with several errors. The decoder then attempts to
7 // recover the original data set. The user may select the FEC
8 // scheme from the command-line interface.
9 // SEE ALSO: crc_example.c
10 // checksum_example.c
11 // packetizer_example.c
12 //
13
14 #include <stdio.h>
15 #include <stdlib.h>
16 #include <string.h>
17 #include <getopt.h>
18
19 #include "liquid.h"
20
21 // print usage/help message
usage()22 void usage()
23 {
24 printf("fec_example [options]\n");
25 printf(" u/h : print usage\n");
26 printf(" n : input data size (number of uncoded bytes)\n");
27 printf(" c : coding scheme, (h74 default):\n");
28 liquid_print_fec_schemes();
29 }
30
31
main(int argc,char * argv[])32 int main(int argc, char*argv[])
33 {
34 // options
35 unsigned int n = 4; // data length (bytes)
36 unsigned int nmax = 2048; // maximum data length
37 fec_scheme fs = LIQUID_FEC_HAMMING74; // error-correcting scheme
38
39 int dopt;
40 while((dopt = getopt(argc,argv,"uhn:c:")) != EOF){
41 switch (dopt) {
42 case 'h':
43 case 'u': usage(); return 0;
44 case 'n': n = atoi(optarg); break;
45 case 'c':
46 fs = liquid_getopt_str2fec(optarg);
47 if (fs == LIQUID_FEC_UNKNOWN) {
48 fprintf(stderr,"error: unknown/unsupported fec scheme \"%s\"\n\n",optarg);
49 exit(1);
50 }
51 break;
52 default:
53 exit(1);
54 }
55 }
56
57 // ensure proper data length
58 n = (n > nmax) ? nmax : n;
59
60 // create arrays
61 unsigned int n_enc = fec_get_enc_msg_length(fs,n);
62 printf("dec msg len : %u\n", n);
63 printf("enc msg len : %u\n", n_enc);
64 unsigned char data[n]; // original data message
65 unsigned char msg_enc[n_enc]; // encoded data message
66 unsigned char msg_cor[n_enc]; // corrupted data message
67 unsigned char msg_dec[n]; // decoded data message
68
69 // create object
70 fec q = fec_create(fs,NULL);
71 fec_print(q);
72
73 unsigned int i;
74
75 // create message
76 for (i=0; i<n; i++)
77 data[i] = rand() & 0xff;
78
79 // encode message
80 fec_encode(q, n, data, msg_enc);
81
82 // corrupt encoded message
83 memmove(msg_cor, msg_enc, n_enc);
84 msg_cor[0] ^= 0x04; // position 5
85 #if 0
86 msg_cor[1] ^= 0x04; //
87 msg_cor[2] ^= 0x02; //
88 msg_cor[3] ^= 0x01; //
89 msg_cor[4] ^= 0x80; //
90 msg_cor[5] ^= 0x40; //
91 msg_cor[6] ^= 0x20; //
92 msg_cor[7] ^= 0x10; //
93 #endif
94
95 // decode message
96 fec_decode(q, n, msg_cor, msg_dec);
97
98 printf("original message: [%3u] ",n);
99 for (i=0; i<n; i++)
100 printf(" %.2X", (unsigned int) (data[i]));
101 printf("\n");
102
103 printf("encoded message: [%3u] ",n_enc);
104 for (i=0; i<n_enc; i++)
105 printf(" %.2X", (unsigned int) (msg_enc[i]));
106 printf("\n");
107
108 printf("corrupted message: [%3u] ",n_enc);
109 for (i=0; i<n_enc; i++)
110 printf("%c%.2X", msg_cor[i]==msg_enc[i] ? ' ' : '*', (unsigned int) (msg_cor[i]));
111 printf("\n");
112
113 printf("decoded message: [%3u] ",n);
114 for (i=0; i<n; i++)
115 printf("%c%.2X", msg_dec[i] == data[i] ? ' ' : '*', (unsigned int) (msg_dec[i]));
116 printf("\n");
117 printf("\n");
118
119 // count bit errors
120 unsigned int j, num_sym_errors=0, num_bit_errors=0;
121 unsigned char e;
122 for (i=0; i<n; i++) {
123 num_sym_errors += (data[i] == msg_dec[i]) ? 0 : 1;
124
125 e = data[i] ^ msg_dec[i];
126 for (j=0; j<8; j++) {
127 num_bit_errors += e & 0x01;
128 e >>= 1;
129 }
130 }
131
132 //printf("number of symbol errors detected: %d\n", num_errors_detected);
133 printf("number of symbol errors received: %3u / %3u\n", num_sym_errors, n);
134 printf("number of bit errors received: %3u / %3u\n", num_bit_errors, n*8);
135
136 // clean up objects
137 fec_destroy(q);
138
139 return 0;
140 }
141
142