magic number
1. In ef="module.php?name=Lexikon&file=search&eid=1&query=source code">source code, some non-obvious constant whose value is significant to the operation of a program and that is inserted inconspicuously in-line (ef="module.php?name=Lexikon&file=search&eid=1&query=hard-coded">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 ef="module.php?name=Lexikon&file=search&eid=1&query=algorithm">algorithm in some opaque way. The classic examples of these are the numbers used in ef="module.php?name=Lexikon&file=search&eid=1&query=hash">hash or ef="module.php?name=Lexikon&file=search&eid=1&query=CRC">CRC functions or the coefficients in a ef="module.php?name=Lexikon&file=search&eid=1&query=linear congruential generator">linear congruential generator for ef="module.php?name=Lexikon&file=search&eid=1&query=pseudo-random">pseudo-random numbers. This sense actually predates, and was ancestral to, the more common sense 1. 3. Special data located at the beginning of a ef="module.php?name=Lexikon&file=search&eid=1&query=binary">binary data file to indicate its type to a utility. Under ef="module.php?name=Lexikon&file=search&eid=1&query=Unix">Unix, the system and various ef="module.php?name=Lexikon&file=search&eid=1&query=applications programs">applications programs (especially the ef="module.php?name=Lexikon&file=search&eid=1&query=linker">linker) distinguish between types of executable file by looking for a magic number. Once upon a time, these magic numbers were ef="module.php?name=Lexikon&file=search&eid=1&query=PDP-11">PDP-11 branch instructions that skipped over header data to the start of executable code 0407, for example, was ef="module.php?name=Lexikon&file=search&eid=1&query=octal">octal for "branch 16 bytes relative". Nowadays only a ef="module.php?name=Lexikon&file=search&eid=1&query=wizard">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]. [ef="module.php?name=Lexikon&file=search&eid=1&query=Jargon File">Jargon File] (2003-07-02) e="border-width:thin; border-color:#333333; border-style:dashed; padding:5px;" align="left">In addition suitable contents:
[ ef="module.php?name=Lexikon&op=content&tid=31">2 ] [ ef="module.php?name=Lexikon&op=content&tid=134">= ] [ ef="module.php?name=Lexikon&op=content&tid=262">ad ] [ ef="module.php?name=Lexikon&op=content&tid=396">ag ] [ ef="module.php?name=Lexikon&op=content&tid=433">al ] [ ef="module.php?name=Lexikon&op=content&tid=492">algorithm ] [ ef="module.php?name=Lexikon&op=content&tid=544">am ] [ ef="module.php?name=Lexikon&op=content&tid=592">an ] [ ef="module.php?name=Lexikon&op=content&tid=683">app ] [ ef="module.php?name=Lexikon&op=content&tid=700">application ] [ ef="module.php?name=Lexikon&op=content&tid=738">aq ] [ ef="module.php?name=Lexikon&op=content&tid=740">ar ] [ ef="module.php?name=Lexikon&op=content&tid=743">arc ] [ ef="module.php?name=Lexikon&op=content&tid=759">arg ] [ ef="module.php?name=Lexikon&op=content&tid=800">as ] [ ef="module.php?name=Lexikon&op=content&tid=822">ash ] [ ef="module.php?name=Lexikon&op=content&tid=894">at ] [ ef="module.php?name=Lexikon&op=content&tid=1026">b ] [ ef="module.php?name=Lexikon&op=content&tid=1034">ba ] [ ef="module.php?name=Lexikon&op=content&tid=1181">be ] [ ef="module.php?name=Lexikon&op=content&tid=1269">bi ] [ ef="module.php?name=Lexikon&op=content&tid=1298">binary ] [ ef="module.php?name=Lexikon&op=content&tid=1444">bo ] [ ef="module.php?name=Lexikon&op=content&tid=1535">br ] [ ef="module.php?name=Lexikon&op=content&tid=1550">branch ] [ ef="module.php?name=Lexikon&op=content&tid=1691">bv ] [ ef="module.php?name=Lexikon&op=content&tid=1695">by ] [ ef="module.php?name=Lexikon&op=content&tid=1699">byte ] [ ef="module.php?name=Lexikon&op=content&tid=1708">C ] [ ef="module.php?name=Lexikon&op=content&tid=1724">ca ] [ ef="module.php?name=Lexikon&op=content&tid=1813">capacity ] [ ef="module.php?name=Lexikon&op=content&tid=1863">cat ] [ ef="module.php?name=Lexikon&op=content&tid=2001">ch ] [ ef="module.php?name=Lexikon&op=content&tid=2099">ci ] [ ef="module.php?name=Lexikon&op=content&tid=2138">cl ] [ ef="module.php?name=Lexikon&op=content&tid=2145">class ] [ ef="module.php?name=Lexikon&op=content&tid=2147">classic ] [ ef="module.php?name=Lexikon&op=content&tid=2247">co ] [ ef="module.php?name=Lexikon&op=content&tid=2273">code ] [ ef="module.php?name=Lexikon&op=content&tid=2287">codes ] [ ef="module.php?name=Lexikon&op=content&tid=2330">com ] [ ef="module.php?name=Lexikon&op=content&tid=2352">comment ] [ ef="module.php?name=Lexikon&op=content&tid=2545">con ] [ ef="module.php?name=Lexikon&op=content&tid=2606">cons ] [ ef="module.php?name=Lexikon&op=content&tid=2790">CR ] [ ef="module.php?name=Lexikon&op=content&tid=2791">cr ] [ ef="module.php?name=Lexikon&op=content&tid=2807">CRC ] [ ef="module.php?name=Lexikon&op=content&tid=2900">cu ] [ ef="module.php?name=Lexikon&op=content&tid=2976">D ] [ ef="module.php?name=Lexikon&op=content&tid=3006">data ] [ ef="module.php?name=Lexikon&op=content&tid=3096">date ] [ ef="module.php?name=Lexikon&op=content&tid=3151">de ] [ ef="module.php?name=Lexikon&op=content&tid=3304">design ] [ ef="module.php?name=Lexikon&op=content&tid=3384">digit ] [ ef="module.php?name=Lexikon&op=content&tid=3565">do ] [ ef="module.php?name=Lexikon&op=content&tid=3623">DOS ] [ ef="module.php?name=Lexikon&op=content&tid=3657">DP ] [ ef="module.php?name=Lexikon&op=content&tid=3752">du ] [ ef="module.php?name=Lexikon&op=content&tid=3865">ec ] [ ef="module.php?name=Lexikon&op=content&tid=3896">ed ] [ ef="module.php?name=Lexikon&op=content&tid=3929">ee ] [ ef="module.php?name=Lexikon&op=content&tid=3946">eg ] [ ef="module.php?name=Lexikon&op=content&tid=4068">encode ] [ ef="module.php?name=Lexikon&op=content&tid=4148">er ] [ ef="module.php?name=Lexikon&op=content&tid=4150">era ] [ ef="module.php?name=Lexikon&op=content&tid=4171">es ] [ ef="module.php?name=Lexikon&op=content&tid=4199">et ] [ ef="module.php?name=Lexikon&op=content&tid=4279">exec ] [ 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ef="module.php?name=Lexikon&op=content&tid=5525">hash ] [ ef="module.php?name=Lexikon&op=content&tid=5540">hat ] [ ef="module.php?name=Lexikon&op=content&tid=5565">header ] [ ef="module.php?name=Lexikon&op=content&tid=5656">hing ] [ ef="module.php?name=Lexikon&op=content&tid=5675">hm ] [ ef="module.php?name=Lexikon&op=content&tid=5722">hose ] [ ef="module.php?name=Lexikon&op=content&tid=5768">hr ] [ ef="module.php?name=Lexikon&op=content&tid=5791">hu ] [ ef="module.php?name=Lexikon&op=content&tid=5931">id ] [ ef="module.php?name=Lexikon&op=content&tid=5956">ie ] [ ef="module.php?name=Lexikon&op=content&tid=6013">il ] [ ef="module.php?name=Lexikon&op=content&tid=6064">in ] [ ef="module.php?name=Lexikon&op=content&tid=6068">inc ] [ ef="module.php?name=Lexikon&op=content&tid=6194">int ] [ ef="module.php?name=Lexikon&op=content&tid=6274">interface ] [ ef="module.php?name=Lexikon&op=content&tid=6413">io ] [ ef="module.php?name=Lexikon&op=content&tid=6482">is ] [ ef="module.php?name=Lexikon&op=content&tid=6558">it ] [ ef="module.php?name=Lexikon&op=content&tid=6589">J ] [ ef="module.php?name=Lexikon&op=content&tid=6619">jar ] [ ef="module.php?name=Lexikon&op=content&tid=6620">Jargon File ] [ ef="module.php?name=Lexikon&op=content&tid=6789">ke ] [ ef="module.php?name=Lexikon&op=content&tid=6822">ki ] [ ef="module.php?name=Lexikon&op=content&tid=6861">kn ] [ ef="module.php?name=Lexikon&op=content&tid=6918">la ] [ ef="module.php?name=Lexikon&op=content&tid=7023">ld ] [ ef="module.php?name=Lexikon&op=content&tid=7091">Lex ] [ ef="module.php?name=Lexikon&op=content&tid=7107">li ] [ ef="module.php?name=Lexikon&op=content&tid=7151">line ] [ ef="module.php?name=Lexikon&op=content&tid=7176">link ] [ ef="module.php?name=Lexikon&op=content&tid=7184">linker ] [ ef="module.php?name=Lexikon&op=content&tid=7291">logical ] [ ef="module.php?name=Lexikon&op=content&tid=7399">ls ] [ ef="module.php?name=Lexikon&op=content&tid=7415">lu ] [ ef="module.php?name=Lexikon&op=content&tid=7441">ly ] [ ef="module.php?name=Lexikon&op=content&tid=7457">M ] [ ef="module.php?name=Lexikon&op=content&tid=7463">ma ] [ ef="module.php?name=Lexikon&op=content&tid=7521">magic ] [ ef="module.php?name=Lexikon&op=content&tid=7582">man ] [ ef="module.php?name=Lexikon&op=content&tid=7749">memory ] [ ef="module.php?name=Lexikon&op=content&tid=7969">minus ] [ ef="module.php?name=Lexikon&op=content&tid=8019">mm ] [ ef="module.php?name=Lexikon&op=content&tid=8032">mo ] [ ef="module.php?name=Lexikon&op=content&tid=8040">mod ] [ ef="module.php?name=Lexikon&op=content&tid=8079">module ] [ ef="module.php?name=Lexikon&op=content&tid=8167">mp ] [ ef="module.php?name=Lexikon&op=content&tid=8228">ms ] [ ef="module.php?name=Lexikon&op=content&tid=8382">MZ ] [ ef="module.php?name=Lexikon&op=content&tid=8384">N ] [ ef="module.php?name=Lexikon&op=content&tid=8386">na ] [ ef="module.php?name=Lexikon&op=content&tid=8460">nc ] [ ef="module.php?name=Lexikon&op=content&tid=8472">ne ] [ ef="module.php?name=Lexikon&op=content&tid=8622">nf ] [ ef="module.php?name=Lexikon&op=content&tid=8627">ng ] [ ef="module.php?name=Lexikon&op=content&tid=8630">ni ] [ ef="module.php?name=Lexikon&op=content&tid=8660">nl ] [ ef="module.php?name=Lexikon&op=content&tid=8672">nn ] [ ef="module.php?name=Lexikon&op=content&tid=8675">no ] [ ef="module.php?name=Lexikon&op=content&tid=8760">ns ] [ ef="module.php?name=Lexikon&op=content&tid=8787">nu ] [ ef="module.php?name=Lexikon&op=content&tid=8799">numbers ] [ ef="module.php?name=Lexikon&op=content&tid=8820">O ] [ ef="module.php?name=Lexikon&op=content&tid=8910">octal ] [ ef="module.php?name=Lexikon&op=content&tid=8964">om ] [ ef="module.php?name=Lexikon&op=content&tid=9014">op ] [ ef="module.php?name=Lexikon&op=content&tid=9120">org ] [ ef="module.php?name=Lexikon&op=content&tid=9132">OS ] [ ef="module.php?name=Lexikon&op=content&tid=9204">pa ] [ ef="module.php?name=Lexikon&op=content&tid=9430">PD ] [ ef="module.php?name=Lexikon&op=content&tid=9445">PDP ] [ ef="module.php?name=Lexikon&op=content&tid=9447">PDP-11 ] [ ef="module.php?name=Lexikon&op=content&tid=9457">pe ] [ ef="module.php?name=Lexikon&op=content&tid=9550">ph ] [ ef="module.php?name=Lexikon&op=content&tid=9651">pl ] [ ef="module.php?name=Lexikon&op=content&tid=9736">plus ] [ ef="module.php?name=Lexikon&op=content&tid=9908">pr ] [ ef="module.php?name=Lexikon&op=content&tid=9995">process ] [ ef="module.php?name=Lexikon&op=content&tid=10000">processing ] [ ef="module.php?name=Lexikon&op=content&tid=10023">program ] [ ef="module.php?name=Lexikon&op=content&tid=10042">programming ] [ ef="module.php?name=Lexikon&op=content&tid=10125">pseudo ] [ ef="module.php?name=Lexikon&op=content&tid=10253">query ] [ ef="module.php?name=Lexikon&op=content&tid=10313">random ] [ ef="module.php?name=Lexikon&op=content&tid=10364">rc ] [ ef="module.php?name=Lexikon&op=content&tid=10385">re ] [ ef="module.php?name=Lexikon&op=content&tid=10767">ro ] [ ef="module.php?name=Lexikon&op=content&tid=10887">ru ] [ ef="module.php?name=Lexikon&op=content&tid=10918">S ] [ ef="module.php?name=Lexikon&op=content&tid=11150">se ] [ ef="module.php?name=Lexikon&op=content&tid=11281">set ] [ ef="module.php?name=Lexikon&op=content&tid=11314">sh ] [ ef="module.php?name=Lexikon&op=content&tid=11376">si ] [ ef="module.php?name=Lexikon&op=content&tid=11389">sig ] [ ef="module.php?name=Lexikon&op=content&tid=11510">sk ] [ ef="module.php?name=Lexikon&op=content&tid=11525">sl ] [ ef="module.php?name=Lexikon&op=content&tid=11651">so ] [ ef="module.php?name=Lexikon&op=content&tid=11745">source ] [ ef="module.php?name=Lexikon&op=content&tid=11746">source code ] [ ef="module.php?name=Lexikon&op=content&tid=11789">Spec ] [ ef="module.php?name=Lexikon&op=content&tid=11790">spec ] [ ef="module.php?name=Lexikon&op=content&tid=11825">spell ] [ ef="module.php?name=Lexikon&op=content&tid=11934">st ] [ ef="module.php?name=Lexikon&op=content&tid=12093">string ] [ ef="module.php?name=Lexikon&op=content&tid=12109">struct ] [ ef="module.php?name=Lexikon&op=content&tid=12133">su ] [ ef="module.php?name=Lexikon&op=content&tid=12246">sy ] [ ef="module.php?name=Lexikon&op=content&tid=12312">system ] [ ef="module.php?name=Lexikon&op=content&tid=12359">T ] [ ef="module.php?name=Lexikon&op=content&tid=12369">table ] [ ef="module.php?name=Lexikon&op=content&tid=12416">tar ] [ ef="module.php?name=Lexikon&op=content&tid=12588">th ] [ ef="module.php?name=Lexikon&op=content&tid=12721">to ] [ ef="module.php?name=Lexikon&op=content&tid=12787">tr ] [ ef="module.php?name=Lexikon&op=content&tid=12873">tron ] [ ef="module.php?name=Lexikon&op=content&tid=12939">tw ] [ ef="module.php?name=Lexikon&op=content&tid=12970">type ] [ ef="module.php?name=Lexikon&op=content&tid=12986">ua ] [ ef="module.php?name=Lexikon&op=content&tid=13030">um ] [ ef="module.php?name=Lexikon&op=content&tid=13146">up ] [ 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