Late Letter Ballot comment on SBC-3
Ralph Weber
Ralph.Weber at wdc.com
Thu Jul 11 15:35:00 PDT 2013
Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1307111_f.htm">HTML-formatted message</a>
In SBC-3 r35 table 21, one finds the following definition of the DIF CRC
generator polynomial:
G(x) = x^16 + x^15 + x^11 + x^9 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
(i.e., G(x) = 1_8BB7h)
With apologies for the lack of good superscripts in e-mail.
For reasons that will become obvious in a day or two, I have recently been
obliged to learn things I really had hoped to avoid knowing about CRC
generator polynomials. In the early going, my knee-jerk reaction to the 'G(x)
= 1_8BB7h' was something like "G(x) does not return a constant value", but I
was at a loss for a better phrasing. No more!
Remembering that x=x^1 and 1=x^0, the 1_8BB7h value is derived as follows:
Exponents 1 1111 1100 0000 0000
of x 6 5432 1098 7654 3210
Bitmask 1 1000 1011 1011 0111
Hex 1 8 B B 7
With this in mind, I request that the SBC-3 table 21 generator i.e. be
modified to read as follows:
(i.e., the bitmask representation of G(x) is 1_8BB7h)
All the best,
.Ralph
P.S. I have see some evidence that the bitmask representation is very useful
is one is building an analog engine to compute the CRC.
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