Landon Curt Noll
ffb738af07
Changed the model of `status.json` model.
Updated `status.json` IOCCC_status_version from "0.2 2023-05-22"
to "1.0 2024-03-09".
Updated FAQ 2.6, improving how IOCCC entries announced.
Moved `bin/ioccc-status.sh` to `tmp/ioccc-status.sh`
now that we have a new status.json model for
which this tool no longer fits (sorry tm Canada 🇨🇦).
Added `status.md` markdown to explain the `status.json` model.
Added `status.html` to both display the contents of `status.json`
and render the contents of `status.md` as HTML.
Added `bin/status2html.sh` to convert `status.json`
into HTML for the `status.html` file.
Added `bin/gen-status.sh` to form `status.json`
and `status.html` files.
Added `make gen_status` to top level Makefile.
Performed `make www` to complete all of the above.
To build:
make all
To use:
./tomtorfs filename bitwidth polynom reflected init xor
where:
filename : file to calculate the CRC of
bitwidth : width of the CRC in bits (decimal)
polynom : polynomial used for the CRC (hexadecimal)
reflected : 0 if the CRC is not reflected, 1 if it is
init : initial value for the CRC (hexadecimal)
xor : value to xor the final CRC with (hexadecimal)
Try:
./try.sh
Judges' remarks:
If you don't believe the program is correct, try and compare the output of the program with the value of CRCs computed by PKZIP or any other archiver that uses the CRC-32 algorithm.
Author's remarks:
Usage:
./tomtorfs filename bitwidth polynom reflected init xor
filename : file to calculate the CRC of
bitwidth : width of the CRC in bits (decimal)
polynom : polynomial used for the CRC (hexadecimal)
reflected : 0 if the CRC is not reflected, 1 if it is
init : initial value for the CRC (hexadecimal)
xor : value to xor the final CRC with (hexadecimal)
Examples
CRC-16:
./tomtorfs filename 16 1021 0 FFFF 0000
CRC-32:
./tomtorfs filename 32 04C11DB7 1 FFFFFFFF FFFFFFFF
XMODEM:
./tomtorfs filename 16 8408 1 0000 0000
ARC:
./tomtorfs filename 16 8005 1 0000 0000
Portability notes
The program assumes CHAR_BIT==8. Results are undefined if bitwidth > sizeof(unsigned long) * 8. It is also assumed that EOF is -1 and 1 is a
valid exit value to indicate failure (replace them with EOF resp.
EXIT_FAILURE if the assumptions are false). Otherwise ANSI/ISO C.
No special build options required.
Special notes
Count the number of non-whitespace characters in the source file to find out what dark force drove me to write this ;-).
Spoiler
First of all, if you run a C beautifier on the program (thereby of course losing the nice code shape I worked so hard on ;-) ) the code will become a bit more readable.
The variable names are not very descriptive. They have the following meanings:
a = argc
A = argv
b = array of unsigned long variables
b[0] = bit-width of the CRC (argv[2])
b[1] = CRC polynomial (argv[3])
b[2] = nonzero if CRC is reflected (argv[4])
b[3] = initial value of CRC (argv[5])
b[4] = value final CRC is XORed with (argv[6])
b[5] = CRC value
b[6] = byte from file
b[7] = counter
B = FILE * through which the file argv[1] is opened
C = typedef for unsigned long
The first for loop simply reads the command-line arguments
in the b[] array. The third parameter to strtoul(3) causes
all arguments to be in base-16 (hex) except the first one,
which will be in base-10 (decimal).
The rest of the program "simply" calculates the CRC in b[5]
and then prints it to stdout. The bit reflection loops may
appear a bit tricky at first, but if you have a good look
at them they should become obvious also.
Acknowledgments:
Ross N. Williams, whose CRC guide was very useful to me for writing this. You can find it in crc.txt.
Copyright and CC BY-SA 4.0 License:
This file is Copyright (c) 2023 by Landon Curt Noll. All Rights Reserved. You are free to share and adapt this file under the terms of this license:
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
For more information, see: https://creativecommons.org/licenses/by-sa/4.0/