Redundant code: Difference between revisions

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In [[computer programming]], '''redundant code''' is [[source code]] or compiled code that is unnecessary. Code that can be removed without affecting its desired behavior is redundant.

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==Categories==

'''Redundant code''' is a [[computer programming]] term for code that computes a result that has been previously computed and is currently available, thus the repeated computation of the result is redundant.<ref>[http://doi.acm.org/10.1145/349214.349233 Debray, S. K., Evans, W., Muth, R., and De Sutter, B. 2000. Compiler techniques for code compaction. ACM Trans. Program. Lang. Syst. 22, 2 (Mar. 2000), 378–415.]</ref> If redundant code can be identified then it can be eliminated, reducing the overall computational cost of the program.

Noteble categoreis of redundant code include:

'''Redundant; code'''Recomputing: isRecomputing a [[computer programming]] term for code that computes a resultvalue that has been previously computedbeen and is currently available, thus the repeated computation of the result is redundant.calculated<ref>[http://doi.acm.org/10.1145/349214.349233 Debray, S. K., Evans, W., Muth, R., and De Sutter, B. 2000. Compiler techniques for code compaction. ACM Trans. Program. Lang. Syst. 22, 2 (Mar. 2000), 378–415.]</ref> Ifand redundantis codestill can be identified then it can be eliminated, reducing the overall computational cost of the programavailable.

== Example ==

<source lang="c">

int f (int x)

{

int y=x*2;

return x*2;

}

</source>

The second <tt>x*2</tt> expression is redundant code and can be replaced by a reference to the variable <tt>y</tt>. Alternatively the definition <tt>int y=x*2</tt> can instead be removed.

; [[Dead code]]: Code that is executed but has no external effect; e.g., does not change the output produced by a program.

== Alternate uses of the term ==

{{unreferencedsection|date=October 2008}}

; [[Unreachable code]]: Code that is never executed. Also, called dead code.

The term '''redundant code''' may also be used to described code that has any form of redundancy, such as recomputing a value that has previously been calculated and is still available, code that is never executed, or a result which is executed and not used. Redundant code may also be used to refer to code that is executed but has no effect on the output of a program – however this is usually known as [[dead code]]. A [[NOP]] might be considered to be redundant code that has been explicitly inserted to pad out the [[instruction (computer science)|instruction]] stream or introduce a time delay. [[Identifier]]s that are declared but never referenced are usually termed as [[redundant declaration]]s.

; [[NOP (code)|NOP]] padding: A NOP instruction might be considered redundant if it's for padding. But if the NOP is required for proper functionality then it's not redundant.

; Unused [[identifier]]: Declared, but never referenced is a redundant declaration.

==Examples==

In the following [[C (computer language)|C]] code, the second <code>x * 2</code> expression is redundant code. Line 2 can be removed, or alternatively, line 3 can be changed to {{code| return y;}}.

<syntaxhighlight lang="C" line>

int f foo(int x) {

int y = x * 2;

return x * 2;

}

</syntaxhighlight>

A more subtle example involves the C preprocessor that inserts code before compilation. Consider:

<syntaxhighlight lang="C">

#define min(A,B) ((A)<(B)?(A):(B))

int shorter_magnitude(int a, int b, int c, int d) {

return sqrt(min(a*a + b*b, c*c + d*d));

}

</syntaxhighlight>

After preprocessing, the code expands to code that evaluates both {{code|a*a + b*b}} and {{code|c*c + d*d}} twice. To eliminate the duplicate code, the macro {{code|min}} could ge converted to a function.

<syntaxhighlight lang="C">

int shorter_magnitude(int a, int b, int c, int d) {

return sqrt(((a*a + b*b)<(c*c + d*d)?(a*a + b*b):(c*c + d*d)));

}

</syntaxhighlight>

==See also==

* {{Annotated link |Code bloat}}

*[[Unreachable code]]

* {{Annotated link |Code reuse}}

*[[Dead code]]

* {{Annotated link |Common subexpression elimination}}

* {{Annotated link |Don't repeat yourself}}

* {{Annotated link |Duplicate code}}

* {{Annotated link |Redundancy (information theory)}}

* {{Annotated link |Code refactoring}}

* {{Annotated link |Code smell}}

==References==

{{reflistReflist}}

[[Category:Compiler optimizations]]

[[Category:Software engineering terminologyanomalies]]

[[Category:Source code]]

[[lt:Perteklinis kodas]]

[[nl:Redundante code]]