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-rw-r--r--encode_rs_av.c61
1 files changed, 61 insertions, 0 deletions
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+/* 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];
+}