/* Fast Reed-Solomon encoder for (255,223) CCSDS code on PowerPC G4/G5 using Altivec instructions
 * Copyright 2004, Phil Karn KA9Q
 * May be used under the terms of the GNU Lesser General Public License (LGPL)
 */
#include <stdio.h>
#include <string.h>
#include "fixed.h"

/* Lookup table for feedback multiplications
 * These are the low half of the coefficients. Since the generator polynomial is
 * palindromic, we form it by reversing these on the fly
 */
static union {
  vector unsigned char v;
  unsigned char c[16];
} table[256];

static vector unsigned char reverse = (vector unsigned char)(0, 15, 14, 13, 12,
                                      11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1);
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);

extern data_t CCSDS_alpha_to[];
extern data_t CCSDS_index_of[];
extern data_t CCSDS_poly[];

void rs_init_av()
{
  int i, j;

  /* The PowerPC is big-endian, so the low-order byte of each vector contains the highest order term in the polynomial */
  for (j = 0; j < 16; j++) {
    table[0].c[j] = 0;
    for (i = 1; i < 256; i++) {
      table[i].c[16 - j - 1] = CCSDS_alpha_to[MODNN(CCSDS_poly[j + 1] +
                                              CCSDS_index_of[i])];
    }
  }
#if 0
  for (i = 0; i < 256; i++) {
    printf("table[%3d] = %3vu\n", i, table[i].v);
  }
#endif
}

void encode_rs_av(unsigned char *data, unsigned char *parity, int pad)
{
  union {
    vector unsigned char v[2];
    unsigned char c[32];
  } shift_register;
  int i;

  shift_register.v[0] = (vector unsigned char)(0);
  shift_register.v[1] = (vector unsigned char)(0);

  for (i = 0; i < NN - NROOTS - pad; i++) {
    vector unsigned char feedback0, feedback1;
    unsigned char f;

    f = data[i] ^ shift_register.c[31];
    feedback1 = table[f].v;
    feedback0 = vec_perm(feedback1, feedback1, reverse);

    /* Shift right one byte */
    shift_register.v[1] = vec_perm(shift_register.v[0], shift_register.v[1],
                                   shift_right) ^ feedback1;
    shift_register.v[0] = vec_sro(shift_register.v[0],
                                  (vector unsigned char)(8)) ^ feedback0;
    shift_register.c[0] = f;
  }
  for (i = 0; i < NROOTS; i++) {
    parity[NROOTS - i - 1] = shift_register.c[i];
  }
}