4.4BSD/usr/share/man/cat1/cksum.0

CKSUM(1)                     BSD Reference Manual                     CKSUM(1)

NNAAMMEE
     cckkssuumm - display file checksums and block counts

SSYYNNOOPPSSIISS
     cckkssuumm [--oo [1 | 2]] [_f_i_l_e _._._.]

DDEESSCCRRIIPPTTIIOONN
     The cckkssuumm utility writes to the standard output three whitespace separat-
     ed fields for each input file.  These fields are a checksum CRC, the to-
     tal number of octets in the file and the file name.  If no file name is
     specified, the standard input is used and no file name is written.

     The options are as follows:

     --oo      Use historic algorithms instead of the (superior) default one.

             Algorithm 1 is the algorithm used by historic BSD systems as the
             sum(1) algorithm and by historic AT&T System V UNIX systems as
             the sum algorithm when using the --rr option.  This is a 16-bit
             checksum, with a right rotation before each addition; overflow is
             discarded.

             Algorithm 2 is the algorithm used by historic AT&T System V UNIX
             systems as the default sum algorithm.  This is a 32-bit checksum,
             and is defined as follows:

                   s = sum of all bytes;
                   r = s % 2^16 + (s % 2^32) / 2^16;
                   cksum = (r % 2^16) + r / 2^16;

             Both algorithm 1 and 2 write to the standard output the same
             fields as the default algorithm except that the size of the file
             in bytes is replaced with the size of the file in blocks.  For
             historic reasons, the block size is 1024 for algorithm 1 and 512
             for algorithm 2.  Partial blocks are rounded up.

     The default CRC used is based on the polynomial used for CRC error check-
     ing in the networking standard ISO 8802-3: 1989  The CRC checksum encod-
     ing is defined by the generating polynomial:

           G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
                x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1

     Mathematically, the CRC value corresponding to a given file is defined by
     the following procedure:

           The _n bits to be evaluated are considered to be the coefficients of
           a mod 2 polynomial M(x) of degree _n-1. These _n bits are the bits
           from the file, with the most significant bit being the most signif-
           icant bit of the first octet of the file and the last bit being the
           least significant bit of the last octet, padded with zero bits (if
           necessary) to achieve an integral number of octets, followed by one
           or more octets representing the length of the file as a binary val-
           ue, least significant octet first.  The smallest number of octets
           capable of representing this integer are used.

           M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided
           by G(x) using mod 2 division, producing a remainder R(x) of degree
           <= 31.

           The coefficients of R(x) are considered to be a 32-bit sequence.


           The bit sequence is complemented and the result is the CRC.

     The cckkssuumm utility exits 0 on success, and >0 if an error occurs.

SSEEEE AALLSSOO
     The default calculation is identical to that given in pseudo-code in the
     following ACM article.

     Dilip V. Sarwate, "Computation of Cyclic Redundancy Checks Via Table
     Lookup", _C_o_m_m_u_n_i_c_a_t_i_o_n_s _o_f _t_h_e _A_C_M, August 1988.

SSTTAANNDDAARRDDSS
     The cckkssuumm utility is expected to be POSIX 1003.2 compatible.

HHIISSTTOORRYY
     The cckkssuumm utility appears in 4.4BSD.

4.4BSD                           June 29, 1993                               2