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62 lines
2.0 KiB
62 lines
2.0 KiB
4 months ago
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/* Fast Reed-Solomon encoder for (255,223) CCSDS code on PowerPC G4/G5 using Altivec instructions
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* Copyright 2004, Phil Karn KA9Q
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* May be used under the terms of the GNU Lesser General Public License (LGPL)
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*/
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#include <stdio.h>
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#include <string.h>
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#include "fixed.h"
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/* Lookup table for feedback multiplications
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* These are the low half of the coefficients. Since the generator polynomial is
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* palindromic, we form it by reversing these on the fly
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*/
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static union { vector unsigned char v; unsigned char c[16]; } table[256];
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static vector unsigned char reverse = (vector unsigned char)(0,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1);
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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);
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extern data_t CCSDS_alpha_to[];
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extern data_t CCSDS_index_of[];
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extern data_t CCSDS_poly[];
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void rs_init_av(){
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int i,j;
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/* The PowerPC is big-endian, so the low-order byte of each vector contains the highest order term in the polynomial */
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for(j=0;j<16;j++){
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table[0].c[j] = 0;
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for(i=1;i<256;i++){
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table[i].c[16-j-1] = CCSDS_alpha_to[MODNN(CCSDS_poly[j+1] + CCSDS_index_of[i])];
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}
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}
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#if 0
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for(i=0;i<256;i++){
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printf("table[%3d] = %3vu\n",i,table[i].v);
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}
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#endif
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}
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void encode_rs_av(unsigned char *data,unsigned char *parity,int pad){
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union { vector unsigned char v[2]; unsigned char c[32]; } shift_register;
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int i;
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shift_register.v[0] = (vector unsigned char)(0);
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shift_register.v[1] = (vector unsigned char)(0);
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for(i=0;i<NN-NROOTS-pad;i++){
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vector unsigned char feedback0,feedback1;
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unsigned char f;
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f = data[i] ^ shift_register.c[31];
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feedback1 = table[f].v;
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feedback0 = vec_perm(feedback1,feedback1,reverse);
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/* Shift right one byte */
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shift_register.v[1] = vec_perm(shift_register.v[0],shift_register.v[1],shift_right) ^ feedback1;
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shift_register.v[0] = vec_sro(shift_register.v[0],(vector unsigned char)(8)) ^ feedback0;
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shift_register.c[0] = f;
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}
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for(i=0;i<NROOTS;i++)
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parity[NROOTS-i-1] = shift_register.c[i];
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}
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