fence
1. A sequence of one or more distinguished (out-of-band) characters (or other
data items), used to delimit a piece of data intended to be treated as a unit
(the computer-science literature calls this a "sentinel"). The NUL (ASCII
0000000) character that terminates strings in C is a fence. Hex FF is also
(though slightly less frequently) used this way. See zigamorph.
2. An extra data value inserted in an array or other data structure in order to
allow some normal test on the array's contents also to function as a termination
test. For example, a highly optimised routine for finding a value in an array
might artificially place a copy of the value to be searched for after the last
slot of the array, thus allowing the main search loop to search for the value
without having to check at each pass whether the end of the array had been
reached.
3. [among users of optimising compilers] Any technique, usually exploiting
knowledge about the compiler, that blocks certain optimisations. Used when
explicit mechanisms are not available or are overkill. Typically a hack: "I call
a dummy procedure there to force a flush of the optimiser's register-colouring
info" can be expressed by the shorter "That's a fence procedure".
[Jargon File]
(1999-01-08)
Nearby terms:
feeping creaturism « FEL « femto- « fence »
fencepost error » fepped out » FEPROM
|
