Index mapping: Difference between revisions

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'''Index mapping''' is a [[computer science]] term (also known as a "'''trivial [[hash function]]'''") that is used to describe the mapping{{clarification needed|date=January 2012}} of [[raw data]], used directly as in [[array index]], for an [[array data structure|array]]. The technique can be most effective for mapping data with a small range{{clarification needed|date=January 2012}}. If the array encompasses all combinations of input, a range check is not required.

'''Index mapping''' is a [[computer science]] term (also known as a "'''trivial [[hash function]]'''") that is used to describe the mapping{{clarification neededclarify|date=January 2012}} of [[raw data]], used directly as in [[array index]], for an [[array data structure|array]]. The technique can be most effective for mapping data with a small range{{clarification neededclarify|date=January 2012}}. If the array encompasses all combinations of input, a range check is not required.

==Applicable arrays==

In practice there are many examples of data exhibiting a small range of valid values all of which are suitable for processing{{clarification needed|date=January 2012}} using a trivial hash function including:

==Applicable arrays==

In practice there are many examples of data exhibiting a small range of valid values all of which are suitable for processing{{clarification neededclarify|date=January 2012}} using a trivial hash function including:

* [[month]] in the year (1–12) – see [[#C example 1|C examples]] below

* [[day]] in the month (1–31)

* [[day of the week]] (1–7)

* human lifespan{{clarification neededclarify|date=January 2012}} (0–130) – e.g. lifecover actuary tables, fixed term mortgage

* [[ASCII]] characters {{clarification neededclarify|date=January 2012}} (0–127), encompassing common mathematical operator symbols, digits, punctuation marks and English language alphabet

* [[EBCDIC]] characters {{clarification neededclarify|date=January 2012}} (0–255)

==Examples==

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*[[Multiway branch]]

*[[lookup table]]

==References==

{{Reflist}}

==External links==

*[http://ols.fedoraproject.org/GCC/Reprints-2008/sayle-reprint.pdf A Superoptimizer Analysis of Multiway Branch Code Generation] by Roger Anthony Sayle

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[[Category:Arrays]]

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[[Category:Hashing|*]]

[[Category:Search algorithms]]

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