crc16.cc: add ccitt16

crc16.cc

@@ -4,41 +4,91 @@
 
 #include <octave/oct.h>
 
-DEFUN_DLD (crc16, args, nargout,
-           "-*- texinfo -*-\n\
-@deftypefn  {Loadable Function} {[@var{c}] =} crc16 (@var{v})\n\
-Dumb CRC16 implementation using polynom\n\
-x^16 + x^15 + x^2 + 1\n\
-@end deftypefn")
-{
-  octave_value_list retval;
-  int nargin = args.length ();
-  if (nargin != 1)
-    {
-      print_usage ();
-      return retval;
-    }
+// http://reveng.sourceforge.net/crc-catalogue/16.htm
 
-  int crc = 0;
-  std::string v = args(0).string_value ();
-  const char *p = v.c_str ();
-  for (int k=0; k < v.length(); ++k)
+// only reflected in and output
+uint16_t __crc16__ (const char *p, size_t len, uint16_t rev_poly, int16_t initial)
+{
+  uint16_t crc = initial;
+  for (int k=0; k < len; ++k)
     {
       int i;
       crc ^= p[k];
       for (i = 0; i < 8; ++i)
         {
           if (crc & 1)
-            crc = (crc >> 1) ^ 0xA001;
+            crc = (crc >> 1) ^ rev_poly;
           else
             crc = (crc >> 1);
         }
     }
-  retval = ovl (crc);
-  return retval;
+  return crc;
+}
+
+uint16_t __crc16_ccitt__ (const char *p, size_t len)
+{
+  uint16_t crc = 0xFFFF;
+  for (int k=0; k < len; ++k)
+    {
+      uint8_t data = p[k];
+      data ^= crc & 0xFF;
+      data ^= data << 4;
+      crc = ((((uint16_t)data << 8) | (crc >> 8) ) ^ (uint8_t)(data >> 4) 
+            ^ ((uint16_t)data << 3));
+    }
+  return crc;
+}
+
+DEFUN_DLD (crc16, args, nargout,
+           "-*- texinfo -*-\n\
+@deftypefn  {Loadable Function} {[@var{c}] =} crc16 (@var{v}, @var{id})\n\
+\n\
+Calculate CRC16 with given ID\n\
+\n\
+@table @asis\n\
+@item ARC, CRC-16, CRC-IBM\n\
+x^16 + x^15 + x^2 + 1 (rev_poly = 0xA001, init = 0)\n\
+\n\
+@item DNP\n\
+rev_poly = 0x8408, init = 0xFFFF)\n\
+\n\
+@item CCITT\n\
+x^16 + x^12 + x^5 + 1 (rev_poly = 0x8408, init = 0xFFFF)\n\
+@end table\n\
+@end deftypefn")
+{
+  int nargin = args.length ();
+  uint16_t ret = 0;
+
+  if (nargin == 2)
+    {
+      std::string v = args(0).string_value ();
+      std::string id = args(1).string_value ();
+      if (id == "ARC" || id == "CRC-16" || id == "CRC-IBM")
+        {
+          ret = __crc16__ (v.c_str (), v.length (), 0xA001, 0);
+        }
+      else if (id == "CCITT")
+        {
+          ret = __crc16_ccitt__ (v.c_str (), v.length ());
+        }
+      else
+        error ("Unkown ID '%s'", id.c_str ());
+    }
+  else
+    {
+      print_usage ();
+      return octave_value ();
+    }
+
+  return ovl(ret);
 }
 
 /*
 %!test
-%! assert (crc16 ("hello world"), 0x39C1);
+%! assert (crc16 ("hello world", "CRC-IBM"), 0x39C1);
+
+%!test
+%! assert (crc16 ("hello world", "CCITT"), 0xEFEB);
+
 */