76 lines
2.3 KiB
C
76 lines
2.3 KiB
C
/* 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 {
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vector unsigned char v;
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unsigned char c[16];
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} table[256];
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static vector unsigned char reverse = (vector unsigned char)(0, 15, 14, 13, 12,
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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,
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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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{
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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] +
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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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{
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union {
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vector unsigned char v[2];
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unsigned char c[32];
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} 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],
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shift_right) ^ feedback1;
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shift_register.v[0] = vec_sro(shift_register.v[0],
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(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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}
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