eight from FOLDOC

eight-bit clean

A term which describes a system that deals correctly with extended character sets which (unlike ASCII) use all eight bits of a byte. Many programs and communications systems assume that all characters have codes in the range 0 to 127. This leaves the top bit of each byte free for use as a parity bit or some kind of flag bit. These assumptions break down when the program is used in some non-english-speaking countries with larger alphabets.

If a binary file is transmitted via a communications link which is not eight-bit clean, it will be corrupted. To combat this you can encode it with uuencode which uses only ASCII characters. There are some links however which are not even "seven-bit clean" and cause problems even for uuencoded data.

Last updated: 1995-01-05

eight queens problem

eight queens puzzle

<algorithm>

A puzzle in which one has to place eight queens on a chessboard such that no queen is attacking any other, i.e. no two queens occupy the same row, column or diagonal. One may have to produce all possible such configurations or just one.

It is a common students assignment to devise a program to solve the eight queens puzzle. The brute force algorithm tries all 64*63*62*61*60*59*58*57 = 178,462,987,637,760 possible layouts of eight pieces on a chessboard to see which ones meet the criterion. More intelligent algorithms use the fact that there are only ten positions for the first queen that are not reflections of each other, and that the first queen leaves at most 42 safe squares, giving only 10*42*41*40*39*38*37*36 = 1,359,707,731,200 layouts to try, and so on.

The puzzle may be varied with different number of pieces and different size boards.

[Best algorithm?]

Last updated: 1999-07-28

eighty-column mind

<abuse>

The sort said to be possessed by persons for whom the transition from punched card to paper tape was traumatic (nobody has dared tell them about disks yet). It is said that these people, including (according to an old joke) the founder of IBM, will be buried "face down, 9-edge first" (the 9-edge being the bottom of the card). This directive is inscribed on IBM's 1402 and 1622 card readers and is referenced in a famous bit of doggerel called "The Last Bug", the climactic lines of which are as follows:

  He died at the console
  Of hunger and thirst.
  Next day he was buried,
  Face down, 9-edge first.

The eighty-column mind is thought by most hackers to dominate IBM's customer base and its thinking.

See fear and loathing, card walloper.

[Jargon File]

Last updated: 1996-08-16

eighty-twenty rule

<programming>

The program-design version of the law of diminishing returns. The 80/20 rule says that roughly 80% of the problem can be solved with 20% of the effort that it would take to solve the whole problem.

For example, parsing e-mail addresses in "From:" lines in e-mail messages is notoriously difficult if you follow the RFC 2822 specification. However, about 60% of actual "From:" lines are in the format "From: Their Name <user@host>", with a far more constrained idea of what can be in "user" or "host" than in RFC 2822. Another 25% just add double-quotes around "Their Name". Matching just those two patterns would thus cover 85% of "From:" lines, with a tiny portion of the code required to fully implement RFC2822.

(Adding support for "From: user@host" and "From: user@host (Their Name) " brings coverage to almost 100%, leaving only really baroque things that RFC-2822 permits, like "From: Pete(A wonderful \) chap) <pete(his account)@silly.test(his host)" or the like.)

It is an eternal question whether too much attention is paid to the 80/20 rule (leading to systems that are irrevocably broken for "unusual" cases), or too little (leading to systems that sacrifice usability in the typical case, just so that rare cases can work properly).

Compare: KISS Principle

Last updated: 2003-11-17

Nearby terms:

eigenvector ♦ eight-bit clean ♦ eight queens problem ♦ eight queens puzzle

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