CRC calculation

CRC parameters

CRC order (1..)
CRC polynom (hex)

Initial value (hex) nondirect direct
Final XOR value (hex)
Bit reversing reverse data bytes reverse CRC result before Final XOR
Presets
The shift direction is left-shift, for both data bytes and CRC result. Reversing data bytes and CRC result has the same effect as right-shifting.

Data sequence

Result

Version updates

110708: Removed copy-and-paste programming style, shortens the source (h#s), variable CRC length (N bytes, see source code)
The USB CRC does not work as implemented algorithm, so it produces wrong output.
030721: question#1: how is a crc polynom correctly reflected if the LSB is not 1 (but the high-bit of the polynom is always assumed as 1)??
030721: question#2: in c-code, be careful using polynoms having a LSB of 0 (e. g. XMODEM 0x8408)... code doesn't work for such cases!!! Any ideas how to convert direct to nondirect values with polynoms having LSB=0?
030721: removed bug in reflect() in javascript code, affecting final crc reflecting of crc orders with order%7 != 0
030204: outcommented the "LSB=1 test" in JAVASCRIPT and C code
030118: included crc masking after converting non-direct to direct initial crc (c-code only, javascript-code is and was correct)
030117: included comment concerning standard parameter set values (like CRC-CCITT), see below; included new links to crc pages
030113: in crctester.c: most of the int's replaced by unsigned longs to avoid compilation errors (especially on 16 bit machines)

This CRC calculator shall support hardware and software designers to check their specific CRC routine. Most of the theory for the JAVASCRIPT and the C code below is taken from the well-known PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS article written by Ross N. Williams.

Notes

The calculator has the following features:

CRC polynoms with orders of 1...64 (counted without the leading '1' bit).
reversed CRC polynoms can be easily determined.
initial and final XOR values can be set.
initial CRC values of algorithms with (click 'nondirect') or without (click 'direct') augmented zero bits can be converted from one into another.
both normal and reflected CRC (refin, refout).
common CRC parameter sets are given by buttons below the parameter table.
(please verify values, there are e. g. different init values for calculating the CRC-CCITT, depending on if the algorithm is direct or indirect. To assign an initial value to the direct or nondirect algorithm, you can click the appropriate radio button on the right side.)
data sequence can be either NULL or a sequence of characters and hexadecimal values between %00...%FF, so is '%31%32%33' the same as '123'.

Furthermore, here is the complete free C CODE of a simple CRC test programm that offer evaluation of different CRC algorithms (bit-by-bit and table-driven, each with and without augmented zero bytes). For the JAVASCRIPT code see the HTML source ;-) I checked the resulting CRC with those values computed by some simple CRC calculators that I found in the internet (see links) and the values given in the PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS article. Anyway, if there are any errors in computing the CRC, either in the above JAVASCRIPT calculator or in the C program, please contact me under zorci@gmx.de.

Finally here are some links to CRC and JAVASCRIPT relavant websites:

   www.iti.fh-flensburg.de/lang/algorithmen/code/crc/crc.htm
   http://www.eagleairaust.com.au/code/crc16.htm
   members.dencity.com/jas/fravia/crctut1.htm
   ftp.std.com/obi/Standards/FileTransfer/XMODEM-CRC.NOTE.1
   www.ross.net/crc/links.html
   www.smbus.org/faq/crc8Applet.htm  (JAVA CRC-8 calculator)
   hyperarchive.lcs.mit.edu/HyperArchive/Archive/per/csmp/csmp-digest-v3-028.txt
   more test case values

   www.teamone.com/selfhtml  (JAVASCRIPT)
   www.netzwelt.com/selfhtml  (JAVASCRIPT)
   www.rabich.de  (JAVASCRIPT)

So have a nice time even in a reflected world :-)
Sven Reifegerste

CRC order (1..)
CRC polynom (hex)
Initial value (hex)		nondirect direct
Final XOR value (hex)
Bit reversing	reverse data bytes reverse CRC result before Final XOR
Presets