GNU Radio's SATELLITES Package

lib/libfec/encode_rs.h
Go to the documentation of this file.
1/* The guts of the Reed-Solomon encoder, meant to be #included
2 * into a function body with the following typedefs, macros and variables supplied
3 * according to the code parameters:
4
5 * data_t - a typedef for the data symbol
6 * data_t data[] - array of NN-NROOTS-PAD and type data_t to be encoded
7 * data_t parity[] - an array of NROOTS and type data_t to be written with parity symbols
8 * NROOTS - the number of roots in the RS code generator polynomial,
9 * which is the same as the number of parity symbols in a block.
10 Integer variable or literal.
11 *
12 * NN - the total number of symbols in a RS block. Integer variable or literal.
13 * PAD - the number of pad symbols in a block. Integer variable or literal.
14 * ALPHA_TO - The address of an array of NN elements to convert Galois field
15 * elements in index (log) form to polynomial form. Read only.
16 * INDEX_OF - The address of an array of NN elements to convert Galois field
17 * elements in polynomial form to index (log) form. Read only.
18 * MODNN - a function to reduce its argument modulo NN. May be inline or a macro.
19 * GENPOLY - an array of NROOTS+1 elements containing the generator polynomial in index
20 form
21
22 * The memset() and memmove() functions are used. The appropriate header
23 * file declaring these functions (usually <string.h>) must be included by the calling
24 * program.
25
26 * Copyright 2004, Phil Karn, KA9Q
27 * May be used under the terms of the GNU Lesser General Public License (LGPL)
28 */
29
30
31#undef A0
32#define A0 (NN) /* Special reserved value encoding zero in index form */
33
34{
35 int i, j;
36 data_t feedback;
37
38 memset(parity, 0, NROOTS * sizeof(data_t));
39
40 for (i = 0; i < NN - NROOTS - PAD; i++) {
41 feedback = INDEX_OF[data[i] ^ parity[0]];
42 if (feedback != A0) { /* feedback term is non-zero */
43#ifdef UNNORMALIZED
44 /* This line is unnecessary when GENPOLY[NROOTS] is unity, as it must
45 * always be for the polynomials constructed by init_rs()
46 */
47 feedback = MODNN(NN - GENPOLY[NROOTS] + feedback);
48#endif
49 for (j = 1; j < NROOTS; j++)
50 parity[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS - j])];
51 }
52 /* Shift */
53 memmove(&parity[0], &parity[1], sizeof(data_t) * (NROOTS - 1));
54 if (feedback != A0)
55 parity[NROOTS - 1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])];
56 else
57 parity[NROOTS - 1] = 0;
58 }
59}
NN
#define NN
Definition ccsds.h:3
NROOTS
#define NROOTS
Definition ccsds.h:4
data_t
unsigned char data_t
Definition ccsds.h:1
A0
#define A0
Definition char.h:20
PAD
#define PAD
Definition char.h:19
MODNN
#define MODNN(x)
Definition char.h:8
INDEX_OF
#define INDEX_OF
Definition char.h:13
GENPOLY
#define GENPOLY
Definition char.h:14
ALPHA_TO
#define ALPHA_TO
Definition char.h:12
j
int j
Definition lib/libfec/decode_rs.h:73
i
int i
Definition lib/libfec/decode_rs.h:73
feedback
data_t feedback
Definition lib/libfec/encode_rs.h:36
memset
memset(parity, 0, NROOTS *sizeof(data_t))