init commit

encode.c

@@ -0,0 +1,36 @@
+#include "code.h"
+
+
+static inline int parity(unsigned long long x){
+  return __builtin_parityll(x);
+}
+
+
+// Convolutionally encode a packet. The input data bytes are read
+// high bit first and the encoded packet is written into 'symbols',
+// one symbol per byte. The first symbol is generated from POLY1,
+// the second from POLY2.
+
+// Storing only one symbol per byte uses more space, but it is faster
+// and easier than trying to pack them more compactly.
+int encode(
+   unsigned char *symbols,	// Output buffer, 2*8*nbytes
+   const unsigned char *data,	// Input buffer, nbytes
+   unsigned int nbytes)		// Number of bytes in data
+{
+  unsigned long long encstate;
+  int i;
+  
+  encstate = 0;
+  while(nbytes-- != 0){
+    for(i=7;i>=0;i--){  // Transmit MSB first
+      encstate = ((encstate << 1) | ((*data >> i) & 1));
+      *symbols++ = G1FLIP ^ parity(encstate & POLY1);
+      *symbols++ = G2FLIP ^ parity(encstate & POLY2);
+    }
+    data++;
+  }
+  if((encstate & ((1LL << K) -1)) != 0)
+    return -1;  // Warn if encoder wasn't tailed back to 0
+  return 0;
+}