Hello everybody,
I'm reading and learning a lot about TCP/IP protocols, and i want to know how to calculate the IP header checksum manually. I've searched for it EVERYWHERE! and none of options work.
I've read a function that does it pretty good, but i can't "translate" it into a human form so i can do it manually.
here's the code:
Code:
unsigned short checksum(unsigned short *ptr, int length){
register int sum = 0;
u_short answer = 0;
register u_short *w = ptr;
register int nleft = len;
while(nleft > 1){
sum += *w++;
nleft -= 2;
}
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
answer = ~sum;
return(answer);
}
People, i've tried, i understand and know how to calculate using ones complement, hex conversion, binary conversion, AND, OR, XOR, NOT, and everything, but i can't do this .
Does anyone know the answer to this?
When I run "sum -r" on a file that I've down loaded from the sco website, the 1st set of numbers differs from the checksum on the download page but the
2nd set matches.
If I try to install the patch, I get errors.
Anyone has an answer? (3 Replies)
say i have these many file in a directory named exam.
1)/exam/newfolder/link.txt.
2)/exam/newfolder1/
and i create a tar say exam.tar
well the problem is,
when i read the tar file i dont find any metadata about the directories,as you cannot create a tar containig empty directories.
on the... (2 Replies)
Hello,
I'm trying to create a shell script (#!/bin/sh) which should tell me the age of a file in minutes...
I have a process, which delivers me all 15 minutes a new file and I want to have a monitoring script, which sends me an email, if the present file is older than 20 minutes.
To do... (10 Replies)
Friends,
I need help with the following in UNIX.
Merge all csv files in one folder considering only 1 header row and ignoring header of all other files.
FYI - All files are in same format and contains same headers.
Thank you (4 Replies)
Hello
I am communicating with two devices using my computer over UDP protocol. The application is running fine. When I monitored the UDP traffic using Wireshark software, I found that there were too many Checksum errors.
Please find attached the png file showing this error. I am about to... (0 Replies)
Hi,
I have an input like this
1 2 3 4
2 3 4 5
4 5 6 7
I would like to count the no. of columns and print a header with a prefix "Col".
I would also like to count the no. of rows and print as first column with each line number with a prefix "Row"
So, my output would be
... (2 Replies)
Hello There...
I have a sample input file ..
number:department:amount
125:Market:125.23
126:Hardware store:434.95
127:Video store:7.45
128:Book store:14.32
129:Gasolline:16.10
I will be doing some manipulations on all the records except the header, but the header should always be... (2 Replies)
I've been struggling with this one for quite a while and cannot seem to find a solution for this find/replace scenario. Perhaps I'm getting rusty.
I have a file that contains a number of metrics (exactly 3 fields per line) from a few appliances that are collected in parallel. To identify the... (3 Replies)
Discussion started by: verdepollo
3 Replies
LEARN ABOUT MOJAVE
sum
sum(n) Cyclic Redundancy Checks sum(n)
__________________________________________________________________________________________________________________________________________________NAME
sum - Calculate a sum(1) compatible checksum
SYNOPSIS
package require Tcl 8.2
package require sum ?1.1.0?
::crc::sum ?-bsd | -sysv? ?-format fmt? ?-chunksize size? [ -filename file | -channel chan | string ]
_________________________________________________________________DESCRIPTION
This package provides a Tcl-only implementation of the sum(1) command which calculates a 16 bit checksum value from the input data. The
BSD sum algorithm is used by default but the SysV algorithm is also available.
COMMANDS
::crc::sum ?-bsd | -sysv? ?-format fmt? ?-chunksize size? [ -filename file | -channel chan | string ]
The command takes string data or a file name or a channel and returns a checksum value calculated using the sum(1) algorithm. The
result is formatted using the format(n) specifier provided or as an unsigned integer (%u) by default.
OPTIONS -sysv The SysV algorithm is fairly naive. The byte values are summed and any overflow is discarded. The lowest 16 bits are returned as the
checksum. Input with the same content but different ordering will give the same result.
-bsd This algorithm is similar to the SysV version but includes a bit rotation step which provides a dependency on the order of the data
values.
-filename name
Return a checksum for the file contents instead of for parameter data.
-channel chan
Return a checksum for the contents of the specified channel. The channel must be open for reading and should be configured for
binary translation. The channel will no be closed on completion.
-chunksize size
Set the block size used when reading data from either files or channels. This value defaults to 4096.
-format string
Return the checksum using an alternative format template.
EXAMPLES
% crc::sum "Hello, World!"
37287
% crc::sum -format 0x%X "Hello, World!"
0x91A7
% crc::sum -file sum.tcl
13392
AUTHORS
Pat Thoyts
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category crc of
the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may have for
either package and/or documentation.
SEE ALSO
cksum(n), crc32(n), sum(1)KEYWORDS
checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security, sum
CATEGORY
Hashes, checksums, and encryption
COPYRIGHT
Copyright (c) 2002, Pat Thoyts <patthoyts@users.sourceforge.net>
crc 1.1.0 sum(n)
08-24-2009
.