Node:hairball, Next:hairy, Previous:hair, Up:= H =_The Jargon File, Version 4.2.2, 20 Aug 2000

hairball n.

1. [Fidonet] A large batch of messages that a

store-and-forward network is failing to forward when it should.

Often used in the phrase "Fido coughed up a hairball today",

meaning that the stuck messages have just come unstuck, producing

a flood of mail where there had previously been drought. 2. An

unmanageably huge mass of source code. "JWZ thought the Mozilla

effort bogged down because the code was a huge hairball." 3. Any

large amount of garbage coming out suddenly. "Sendmail is

coughing up a hairball, so expect some slowness accessing the

Internet."

Node:hairy, Next:HAKMEM, Previous:hairball, Up:=

H =

hairy adj.

1. Annoyingly complicated. "DWIM is

incredibly hairy." 2. Incomprehensible. "DWIM is incredibly hairy." 3. Of people,

high-powered, authoritative, rare, expert, and/or

incomprehensible. Hard to explain except in context: "He knows

this hairy lawyer who says there's nothing to worry about." See

also hirsute.

A well-known result in topology called the Brouwer Fixed-Point

Theorem states that any continuous transformation of a 2-sphere

into itself has at least one fixed point. Mathematically literate

hackers tend to associate the term `hairy' with the informal

version of this theorem; "You can't comb a hairy ball

smooth."

The adjective `long-haired' is well-attested to have been in

slang use among scientists and engineers during the early 1950s;

it was equivalent to modern `hairy' senses 1 and 2, and was very

likely ancestral to the hackish use. In fact the noun `long-hair'

was at the time used to describe a person satisfying sense 3.

Both senses probably passed out of use when long hair was adopted

as a signature trait by the 1960s counterculture, leaving hackish

`hairy' as a sort of stunted mutant relic.

In British mainstream use, "hairy" means "dangerous", and

consequently, in British programming terms, "hairy" may be used

to denote complicated and/or incomprehensible code, but only if

that complexity or incomprehesiveness is also considered

dangerous.

Node:HAKMEM, Next:hakspek, Previous:hairy, Up:= H

HAKMEM /hak'mem/ n.

MIT AI Memo 239 (February 1972). A legendary collection of

neat mathematical and programming hacks contributed by many

people at MIT and elsewhere. (The title of the memo really is

"HAKMEM", which is a 6-letterism for `hacks memo'.) Some of them

are very useful techniques, powerful theorems, or interesting

unsolved problems, but most fall into the category of

mathematical and computer trivia. Here is a sampling of the

entries (with authors), slightly paraphrased:

Item 41 (Gene Salamin): There are exactly 23,000 prime numbers

less than 2^(18).

Item 46 (Rich Schroeppel): The most probable suit

distribution in bridge hands is 4-4-3-2, as compared to 4-3-3-3,

which is the most evenly distributed. This is because

the world likes to have unequal numbers: a thermodynamic effect

saying things will not be in the state of lowest energy, but in

the state of lowest disordered energy.

Item 81 (Rich Schroeppel): Count the magic squares of order 5

(that is, all the 5-by-5 arrangements of the numbers from 1 to 25

such that all rows, columns, and diagonals add up to the same

number). There are about 320 million, not counting those that

differ only by rotation and reflection.

Item 154 (Bill Gosper): The myth that any given programming

language is machine independent is easily exploded by computing

the sum of powers of 2. If the result loops with period = 1 with

sign +, you are on a sign-magnitude machine. If the result loops

with period = 1 at -1, you are on a twos-complement machine. If

the result loops with period greater than 1, including the

beginning, you are on a ones-complement machine. If the result

loops with period greater than 1, not including the beginning,

your machine isn't binary -- the pattern should tell you the

base. If you run out of memory, you are on a string or bignum

system. If arithmetic overflow is a fatal error, some fascist pig

with a read-only mind is trying to enforce machine independence.

But the very ability to trap overflow is machine dependent. By

this strategy, consider the universe, or, more precisely,

algebra: Let X = the sum of many powers of 2 =

...111111 (base 2). Now add X to itself: X + X =

...111110. Thus, 2X = X - 1, so X = -1. Therefore

algebra is run on a machine (the universe) that is

two's-complement.

Item 174 (Bill Gosper and Stuart Nelson): 21963283741 is the

only number such that if you represent it on the PDP-10 as both an integer and a floating-point

number, the bit patterns of the two representations are

identical.

Item 176 (Gosper): The "banana phenomenon" was encountered

when processing a character string by taking the last 3 letters

typed out, searching for a random occurrence of that sequence in

the text, taking the letter following that occurrence, typing it

out, and iterating. This ensures that every 4-letter string

output occurs in the original. The program typed

BANANANANANANANA.... We note an ambiguity in the

phrase, "the Nth occurrence of." In one sense, there are five

00's in 0000000000; in another, there are nine. The editing

program TECO finds five. Thus it finds only the first ANA in

BANANA, and is thus obligated to type N next. By Murphy's Law,

there is but one NAN, thus forcing A, and thus a loop. An option

to find overlapped instances would be useful, although it would

require backing up N - 1 characters before seeking the next

N-character string.

Note: This last item refers to a Dissociated Press implementation.