display file checksums and block counts
1 | 2 |
utility writes to the standard output
three whitespace separated fields for each input file. These fields are a
checksum CRC, the total 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
utility is identical to the
utility, except that it defaults to using
historic algorithm 1, as described below. It is provided for compatibility
The options are as follows:
- Use historic algorithms instead of the (superior) default
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(1) algorithm when using the
-r 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(1) algorithm. This is a 32-bit checksum,
and is defined as follows:
Algorithm 3 is what is commonly called the ‘
s = sum of all bytes;
r = s % 2^16 + (s % 2^32) / 2^16;
cksum = (r % 2^16) + r / 2^16;
CRC’ algorithm. This is a 32-bit checksum.
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
The default CRC used is based on the polynomial used for CRC error checking in
the networking standard ISO 8802-3: 1989
The CRC checksum encoding 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
bits to be evaluated are considered to be
the coefficients of a mod 2 polynomial M(x) of degree
-1. These n
bits are the bits from the file, with the most significant bit being the most
significant 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 value, least significant octet
first. The smallest number of octets capable of representing this integer are
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.
utilities exit 0 on success, and >0 if an error occurs.
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, Communications of the Tn ACM,
utility is expected to conform to
IEEE Std 1003.2-1992
utility appeared in