RE: iSCSI CRC considerations

["Douglas Otis" <dotis@sanlight.net>]

Julian,

Page 14:
   "Adler [RFC1150] demands the expensive modulo operation with a very
   large prime, for the processing of each byte, or some test to
   indicate the necessity in that operation. Fletcher [FITS] only
   demands an addition, and can work on 16-bit at a time."

Correction not RFC-1150 but these RFCs reference use of Adler-32: RFC-1950,
RFC-1951, RFC-1952, RFC-1979, RFC-2394, RFC-2960.

Your description of Adler-32 is incorrect with respect to implementation.

#define BASE 65521
...
     s1 += *buf++;
     if (s1 >= BASE)
         s1 -= BASE;
     s2 += s1;
     if (s2 >= BASE)
         s2 -= BASE;
...

This can be done with without table lookup and the speed of calculation is
faster than CRC.  There is NO expensive modulo instruction for Adler-32.

Doug