1 /* Fast Reed-Solomon encoder for (255,223) CCSDS code on PowerPC G4/G5 using Altivec instructions
2 * Copyright 2004, Phil Karn KA9Q
3 * May be used under the terms of the GNU Lesser General Public License (LGPL)
4 */
5 #include <stdio.h>
6 #include <string.h>
7 #include "fixed.h"
8
9 /* Lookup table for feedback multiplications
10 * These are the low half of the coefficients. Since the generator polynomial is
11 * palindromic, we form it by reversing these on the fly
12 */
13 static union { vector unsigned char v; unsigned char c[16]; } table[256];
14
15 static vector unsigned char reverse = (vector unsigned char)(0,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1);
16 static vector unsigned char shift_right = (vector unsigned char)(15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30);
17
18 extern data_t CCSDS_alpha_to[];
19 extern data_t CCSDS_index_of[];
20 extern data_t CCSDS_poly[];
21
rs_init_av()22 void rs_init_av(){
23 int i,j;
24
25 /* The PowerPC is big-endian, so the low-order byte of each vector contains the highest order term in the polynomial */
26 for(j=0;j<16;j++){
27 table[0].c[j] = 0;
28 for(i=1;i<256;i++){
29 table[i].c[16-j-1] = CCSDS_alpha_to[MODNN(CCSDS_poly[j+1] + CCSDS_index_of[i])];
30 }
31 }
32 #if 0
33 for(i=0;i<256;i++){
34 printf("table[%3d] = %3vu\n",i,table[i].v);
35 }
36 #endif
37 }
38
encode_rs_av(unsigned char * data,unsigned char * parity,int pad)39 void encode_rs_av(unsigned char *data,unsigned char *parity,int pad){
40 union { vector unsigned char v[2]; unsigned char c[32]; } shift_register;
41 int i;
42
43 shift_register.v[0] = (vector unsigned char)(0);
44 shift_register.v[1] = (vector unsigned char)(0);
45
46 for(i=0;i<NN-NROOTS-pad;i++){
47 vector unsigned char feedback0,feedback1;
48 unsigned char f;
49
50 f = data[i] ^ shift_register.c[31];
51 feedback1 = table[f].v;
52 feedback0 = vec_perm(feedback1,feedback1,reverse);
53
54 /* Shift right one byte */
55 shift_register.v[1] = vec_perm(shift_register.v[0],shift_register.v[1],shift_right) ^ feedback1;
56 shift_register.v[0] = vec_sro(shift_register.v[0],(vector unsigned char)(8)) ^ feedback0;
57 shift_register.c[0] = f;
58 }
59 for(i=0;i<NROOTS;i++)
60 parity[NROOTS-i-1] = shift_register.c[i];
61 }
62