> sumr computes the same function as > plan 9's sum -r, which is also the same function as > seventh edition's sum. i have always assumed the -r > stood for "research" as in research unix, although > the plan 9 manual describes it as "system v's sum -r" and > other manuals describe it as the "historical bsd algorithm." > it does seem to have appeared first in v7.
The "-r" option was added to the System V "sum", which by default actually does a true modulo 2^16 sum of the bytes, to obtain the Research version. However, I think the "r" may have been meant as a mnemonic for "rotating" rather than "Research"; the "-r" algorithm rotates the accumulator as the bytes are added to it. Of course neither of these is as reliable as a polynomial- based (feedback shift register) checksum for actual checksumming applications.
