diff options
Diffstat (limited to 'encode_rs_av.c')
-rw-r--r-- | encode_rs_av.c | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/encode_rs_av.c b/encode_rs_av.c new file mode 100644 index 0000000..32e528f --- /dev/null +++ b/encode_rs_av.c @@ -0,0 +1,61 @@ +/* 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]; +} |