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A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data integrity but are not relied upon to verify data authenticity .
It worked by breaking up the data to be sent into 128-byte packets, adding a 3-byte header and 1-byte checksum footer, and sending the resulting 132-byte packets out in order. The receiving computer recalculated the checksum from the 128 bytes of data, and if it matched the checksum sent in the footer it sent back an ACK , and if it did not ...
SYSV checksum (Unix) 16 bits sum with circular rotation sum8 8 bits sum Internet Checksum: 16 bits sum (ones' complement) sum24 24 bits sum sum32 32 bits sum fletcher-4: 4 bits sum fletcher-8: 8 bits sum fletcher-16: 16 bits sum fletcher-32: 32 bits sum Adler-32: 32 bits sum xor8: 8 bits sum Luhn algorithm: 1 decimal digit sum Verhoeff ...
Many protocols use an XOR-based longitudinal redundancy check byte (often called block check character or BCC), including the serial line interface protocol (SLIP, not to be confused with the later and well-known Serial Line Internet Protocol), [8] the IEC 62056-21 standard for electrical-meter reading, smart cards as defined in ISO/IEC 7816, and the ACCESS.bus protocol.
Both, IMO. Either can be used to catch some classes of errors in a 1 dimensional sting of bytes. Either can be combined with TRC to correct multiple errors. I don't know which one provides more information; I suspect both are equal for 2D. --Eet 1024 01:16, 26 January 2008 (UTC) 11 years later and this article is still misleading.
The Fletcher checksum cannot distinguish between blocks of all 0 bits and blocks of all 1 bits. For example, if a 16-bit block in the data word changes from 0x0000 to 0xFFFF, the Fletcher-32 checksum remains the same. This also means a sequence of all 00 bytes has the same checksum as a sequence (of the same size) of all FF bytes.
10 0001 0000 1: byte → value push a byte onto the stack as an integer value: breakpoint ca 1100 1010 reserved for breakpoints in Java debuggers; should not appear in any class file caload 34 0011 0100 arrayref, index → value load a char from an array castore 55 0101 0101 arrayref, index, value → store a char into an array checkcast c0 ...
An Adler-32 checksum is obtained by calculating two 16-bit checksums A and B and concatenating their bits into a 32-bit integer. A is the sum of all bytes in the stream plus one, and B is the sum of the individual values of A from each step.