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gen_ccsds_tal.c

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+/* Conversion lookup tables from conventional alpha to Berlekamp's
+ * dual-basis representation. Used in the CCSDS version only.
+ * taltab[] -- convert conventional to dual basis
+ * tal1tab[] -- convert dual basis to conventional
+
+ * Note: the actual RS encoder/decoder works with the conventional basis.
+ * So data is converted from dual to conventional basis before either
+ * encoding or decoding and then converted back.
+ *
+ * Copyright 2002 Phil Karn, KA9Q
+ * May be used under the terms of the GNU Lesser General Public License (LGPL)
+ */
+#include <stdio.h>
+#include <stdlib.h>
+
+#define DTYPE unsigned char
+DTYPE Taltab[256],Tal1tab[256];
+
+static DTYPE tal[] = { 0x8d, 0xef, 0xec, 0x86, 0xfa, 0x99, 0xaf, 0x7b };
+
+/* Generate conversion lookup tables between conventional alpha representation
+ * (@**7, @**6, ...@**0)
+ *  and Berlekamp's dual basis representation
+ * (l0, l1, ...l7)
+ */
+int main(){
+  int i,j,k;
+
+  for(i=0;i<256;i++){/* For each value of input */
+    Taltab[i] = 0;
+    for(j=0;j<8;j++) /* for each column of matrix */
+      for(k=0;k<8;k++){ /* for each row of matrix */
+	if(i & (1<<k))
+	   Taltab[i] ^= tal[7-k] & (1<<j);
+      }
+    Tal1tab[Taltab[i]] = i;
+  }
+  printf("unsigned char Taltab[] = {\n");
+  for(i=0;i<256;i++){
+    if((i % 16) == 0)
+      printf("\n");
+    printf("0x%02x,",Taltab[i]);
+  }
+  printf("\n};\n\nunsigned char Tal1tab[] = {");
+  for(i=0;i<256;i++){
+    if((i % 16) == 0)
+      printf("\n");
+    printf("0x%02x,",Tal1tab[i]);
+  }
+  printf("\n};\n");
+  exit(0);
+}
+