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The effect of a checksum algorithm that yields an n-bit checksum is to map each m-bit message to a corner of a larger hypercube, with dimension m + n. The 2 m + n corners of this hypercube represent all possible received messages. The valid received messages (those that have the correct checksum) comprise a smaller set, with only 2 m corners.
The Internet checksum, [1] [2] also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. It is carried in the IP packet header , and represents the 16-bit result of summation of the header words.
As an example, a Fletcher-16 checksum shall be calculated and verified for a byte stream of 0x01 0x02. ... The below is a treatment on how to calculate the checksum ...
The Verhoeff checksum calculation is performed as follows: Create an array n out of the individual digits of the number, taken from right to left (rightmost digit is n 0, etc.). Initialize the checksum c to zero. For each index i of the array n, starting at zero, replace c with (, (,)) .
This is a list of hash functions, including cyclic redundancy checks, checksum functions, and cryptographic hash functions. This list is incomplete ; you can help by adding missing items . ( February 2024 )
Example of generating an 8-bit CRC. The generator is a Galois-type shift register with XOR gates placed according to powers (white numbers) of x in the generator polynomial. The message stream may be any length. After it has been shifted through the register, followed by 8 zeroes, the result in the register is the checksum.
Adler-32 is a checksum algorithm written by Mark Adler in 1995, [1] modifying Fletcher's checksum. Compared to a cyclic redundancy check of the same length, it trades reliability for speed. Adler-32 is more reliable than Fletcher-16, and slightly less reliable than Fletcher-32. [2]
Here is how to do the checksum calculation: Take the value (0 through 42) of each character in the barcode excluding start and stop codes. Sum the values. Divide the result by 10 (for Mod 10 check digit) or by 43 (for Mod 43 check digit). The remainder is the value of the checksum character to be appended.