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1. WordNet® 3.0 (2006) |
magic number
n 1: the atomic number of an extra stable strongly bound atomic
nucleus: 2, 8, 20, 28, 50, 82 or 126
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2. The Jargon File (version 4.4.7, 29 Dec 2003) |
magic number
n.
[Unix/C; common]
1. In source code, some non-obvious constant whose value is significant to
the operation of a program and that is inserted inconspicuously in-line (
hardcoded), rather than expanded in by a symbol set by a commented #define
. Magic numbers in this sense are bad style.
2. A number that encodes critical information used in an algorithm in some
opaque way. The classic examples of these are the numbers used in hash or
CRC functions, or the coefficients in a linear congruential generator for
pseudo-random numbers. This sense actually predates and was ancestral to
the more common sense
3. Special data located at the beginning of a binary data file to indicate
its type to a utility. Under Unix, the system and various applications
programs (especially the linker) distinguish between types of executable
file by looking for a magic number. Once upon a time, these magic numbers
were PDP-11 branch instructions that skipped over header data to the
start of executable code; 0407, for example, was octal for ?branch 16 bytes
relative?. Many other kinds of files now have magic numbers somewhere; some
magic numbers are, in fact, strings, like the ! at the beginning of a
Unix archive file or the %! leading PostScript files. Nowadays only a
wizard knows the spells to create magic numbers. How do you choose a fresh
magic number of your own? Simple ? you pick one at random. See? It's magic!
4. An input that leads to a computational boundary condition, where
algorithm behavior becomes discontinuous. Numeric overflows (particularly
with signed data types) and run-time errors (divide by zero, stack
overflows) are indications of magic numbers. The Y2K scare was probably the
most notorious magic number non-incident.
The magic number, on the other hand, is 7?2. See The magical number seven,
plus or minus two: some limits on our capacity for processing information
by George Miller, in the Psychological Review 63:81-97 (1956). This classic
paper established the number of distinct items (such as numeric digits)
that humans can hold in short-term memory. Among other things, this
strongly influenced the interface design of the phone system.
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3. The Free On-line Dictionary of Computing (30 December 2018) |
magic number
1. In source code, some non-obvious
constant whose value is significant to the operation of a
program and that is inserted inconspicuously in-line
(hard-coded), rather than expanded in by a symbol set by a
commented "#define". Magic numbers in this sense are bad
style.
2. A number that encodes critical information used in an
algorithm in some opaque way. The classic examples of these
are the numbers used in hash or CRC functions or the
coefficients in a linear congruential generator for
pseudorandom numbers. This sense actually predates, and
was ancestral to, the more common sense 1.
3. Special data located at the beginning of a binary data
file to indicate its type to a utility. Under Unix, the
system and various applications programs (especially the
linker) distinguish between types of executable file by
looking for a magic number. Once upon a time, these magic
numbers were PDP-11 branch instructions that skipped over
header data to the start of executable code; 0407, for
example, was octal for "branch 16 bytes relative". Nowadays
only a wizard knows the spells to create magic numbers. MS
DOS executables begin with the magic string "MZ".
*The* magic number, on the other hand, is 7+/-2. The paper
cited below established the number of distinct items (such as
numeric digits) that humans can hold in short-term memory.
Among other things, this strongly influenced the interface
design of the phone system.
["The magical number seven, plus or minus two: some limits on
our capacity for processing information", George Miller, in
the "Psychological Review" 63:81-97, 1956].
[Jargon File]
(2003-07-02)
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Common Misspellings > |
magic number amagic number amgic number mamgic number agic number mmagic number mgaic number magaic number mgic number maagic number maigc number magigc number maic number maggic number magci number magici number magc number magiic number magi cnumber magic cnumber magi number magicc number magicn umber magic n umber magicnumber magic number magic unmber magic nunmber magic umber magic nnumber magic nmuber magic numuber magic nmber magic nuumber magic nubmer magic numbmer magic nuber magic nummber magic numebr magic numbebr magic numer magic numbber magic numbre magic numbere magic numbr magic numbeer magic numbrer magic numbe magic numberr jagic number mjagic number jmagic number kagic number mkagic number kmagic number lagic number mlagic number lmagic number nagic number mnagic number nmagic number agic number m agic number magic number mqgic number maqgic number mqagic number mwgic number mawgic number mwagic number msgic number masgic number msagic number mxgic number maxgic number mxagic number mzgic number mazgic number mzagic number m gic number ma gic number m agic number megic number migic number mogic number mugic number maric number magric number margic number matic number magtic number matgic number mayic number magyic number maygic number mafic number magfic number mafgic number mahic number maghic number mahgic number mavic number magvic number mavgic number mabic number magbic number mabgic number manic number magnic number mangic number ma ic number mag ic number ma gic number mag8c number magi8c number mag8ic number mag*c number magi*c number mag*ic number mag9c number magi9c number mag9ic number maguc number magiuc number maguic number magoc number magioc number magoic number magjc number magijc number magjic number magkc number magikc number magkic number maglc number magilc number maglic number magac number magec number magis number magics number magisc number magid number magicd number magidc number magif number magicf number magifc number magix number magicx number magixc number magiv number magicv number magivc number magi number magic number magi c number magic gumber magic ngumber magic gnumber magic humber magic nhumber magic hnumber magic jumber magic njumber magic jnumber magic bumber magic nbumber magic bnumber magic mumber magic nmumber magic mnumber magic umber magic n umber magic number magic n7mber magic nu7mber magic n7umber magic n&mber magic nu&mber magic n&umber magic n8mber magic nu8mber magic n8umber magic nymber magic nuymber magic nyumber magic nimber magic nuimber magic niumber magic nhmber magic nuhmber magic nhumber magic njmber magic nujmber magic njumber magic nkmber magic nukmber magic nkumber magic namber magic nember magic nomber magic nujber magic numjber magic nujmber magic nukber magic numkber magic nukmber magic nulber magic numlber magic nulmber magic nunber magic numnber magic nunmber magic nu ber magic num ber magic nu mber magic numfer magic numbfer magic numfber magic numger magic numbger magic numgber magic numher magic numbher magic numhber magic numver magic numbver magic numvber magic numner magic numbner magic numnber magic num er magic numb er magic num ber magic numb3r magic numbe3r magic numb3er magic numb#r magic numbe#r magic numb#er magic numb4r magic numbe4r magic numb4er magic numbwr magic numbewr magic numbwer magic numbrr magic numberr magic numbrer magic numbsr magic numbesr magic numbser magic numbdr magic numbedr magic numbder magic numbfr magic numbefr magic numbfer magic numbar magic numbir magic numbor magic numbur magic numbe4 magic number4 magic numbe4r magic numbe$ magic number$ magic numbe$r magic numbe5 magic number5 magic numbe5r magic numbee magic numbere magic numbeer magic numbet magic numbert magic numbetr magic numbed magic numberd magic numbedr magic numbef magic numberf magic numbefr magic numbeg magic numberg magic numbegr Definition commonly spelled as: Defanition or Defenition, Synonym as: Synonim, Sinonym or Sinonim, Thesaurus as: Thesorus or Thesauris, Dictionary as: Dictionery or Dictionry and Define is usually not misspelled. What does mispell meen? It Meens...
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