CRC for MSDOS & Concurrent PC-DOS
by Howard Vigorita, NYACC CP/M SIG
upload comments, etc. to: (718) 539-3338 (BBS)
This is a MSDOS generic program derived from the CP/M-86
version by Bill Bolton found on SIG/M Volume #210. MSDOS 2.0 or
higher is required for operation. This is a disk file CRC
checking and generating utility originally written for CP/M-80,
CP/M-86, MP/M-86 and Concurrent PCDOS, now available for MSDOS.
Version 6.7 of CRC has also been tested on Concurrent PC-DOS 4.1.
This is a companion utility to CRCBUILD which builds
-CATALOG files. This utility uses those -CATALOG files as an
interactive look up table and displays *MATCH* on your screen
next to each line whose embedded CRC agrees with disk contents.
This utility will optionally create an output file on
the default drive, listing the CRC's of all files checked in a
single session. That output file can also serve as the look up.
COMMANDS:
CRC [drive:]<filename.filetype> [F]
Examples:
CRC Will attempt to find CRCKLIST.???,
or CRCKFILE.??? or -CATALOG.???
and try to match recorded CRC values
in that file with values calculated
on the fly for files on the disk.
CRC MYFILE.ASM Check only MYFILE.ASM
CRC B:*.ASM Check all .ASM files ON B: drive
CRC *.* F Check all files, writing output to a file
Hidden files as well as files with the '$$$' extention are
ignored.
Path names as part of the file specification are not
supported in this version. To check the CRC of files in a
sub-directory, first log in that sub-directory, then run CRC
from a different drive with the drive designation of the sub-
directory as part of the file specification. To run CRC from
the root directory of the A: drive and CRC all files on the
\user\progs\asm sub-directory of the B: drive, do the following:
A>cd B:\user\progs\asm
A>CRC B:*.*
ALGORITHM NOTES
The CYCLIC-REDUNDANCY-CHECK number used in this program
is based on the following CCITT standard polynominal:
X^16 + X^15 + X^13 + X^7 + X^4 + X^2 + X + 1
Special attention in this implementation has been given
to insure that it generates CRC's which are not only compatable
with SIG/M -CATALOG files and XMODEM CRC's, but which are also
communication chanel insensitive. Generated CRC's will remain
unchanged when files are moved from MSDOS or UNIX through
communication's chanels which pad byte resolution to standard
block boundaries. It is thus useful for checking the accuracy of
such file transfers. It is significantly more accurate than a
simple checksum with virtually no speed penalty as well as faster
and less memory intensive than any table lookup technique.
SPECIAL MSDOS NOTE
This CRCK version fixes a bug in some MSDOS versions whereby
partial sectors of files were not being processed. Such versions
generate "00 00" CRC values for files less than 128 bytes in length
and incorrect values for files not an exact multiple of 128 bytes
long. Use this version of CRC with CRCBUILD version 1.1 or greater
which also fixes this bug.
CREDITS
The 8 bit version of the program was originally conceived
by Keith Petersen, W8SDZ, to whom all glory and honour. Due to
the scarcity of source code in the MSDOS public domain, the MSDOS
version of this program has been derived from the CP/M-86 version
by Bill Bolton, Software Tools BBS, Australia. Many thanks to
Bill Bolton and the many other CP/M-86 programmers who continue
enable the rest of us to learn from their examples in the best
spirt of the public domain.