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Redundant code

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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr">In <a href="Computer_programming" title="Computer programming">computer programming</a>, redundant code is <a href="Source_code" title="Source code">source code</a> or compiled code in a <a href="Computer_program" title="Computer program">computer program</a> that is unnecessary, such as:

<ul><li>recomputing a value that has previously been calculated<a href="#cite_note-1">[1]</a> and is still available,</li>

<li>code that is never executed (known as <a href="Unreachable_code" title="Unreachable code">unreachable code</a>),</li>

<li>code which is executed but has no external effect (e.g., does not change the output produced by a program; known as <a href="Dead_code" title="Dead code">dead code</a>).</li></ul>

A <a href="NOP_(code)" title="NOP (code)">NOP</a> instruction might be considered to be redundant code that has been explicitly inserted to pad out the <a href="Instruction_(computer_science)" class="mw-redirect" title="Instruction (computer science)">instruction</a> stream or introduce a time delay, for example to create a timing loop by "wasting time". <a href="Identifier" title="Identifier">Identifiers</a> that are declared, but never referenced, are termed redundant declarations.

<div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2></div>

The following examples are in <a href="C_(computer_language)" class="mw-redirect" title="C (computer language)">C</a>.

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>int foo(int iX)

{

int iY = iX*2;

return iX*2;

}

</pre></div>

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

Consider:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>#define min(A,B) ((A)<(B)?(A):(B))

int shorter_magnitude(int u1, int v1, int u2, int v2)

{

/* Returns the shorter magnitude of (u1,v1) and (u2,v2) */

return sqrt(min(u1*u1 + v1*v1, u2*u2 + v2*v2));

}

</pre></div>

As a consequence of using the <a href="C_preprocessor" title="C preprocessor">C preprocessor</a>, the compiler will only see the expanded form:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>int shorter_magnitude(int u1, int v1, int u2, int v2)

{

int temp;

if (u1*u1 + v1*v1 < u2*u2 + v2*v2)

temp = u1*u1 + v1*v1; /* Redundant already calculated for comparison */

else

temp = u2*u2 + v2*v2; /* Redundant already calculated for comparison */

return sqrt(temp);

}

</pre></div>

Because the use of min/max macros is very common, modern compilers are programmed to recognize and eliminate redundancy caused by their use.

There is no redundancy, however, in the following code:

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>#define max(A,B) ((A)>(B)?(A):(B))

int random(int cutoff, int range)

{

return max(cutoff, rand()%range);

}

</pre></div>

If the initial call to rand(), modulo range, is greater than or equal to cutoff, rand() will be called a second time for a second computation of rand()%range, which may result in a value that is actually lower than the cutoff. The max macro thus may not produce the intended behavior for this function.

<ul><li><a href="Code_bloat" title="Code bloat">Code bloat</a></li>

<li><a href="Code_reuse" title="Code reuse">Code reuse</a></li>

<li><a href="Common_subexpression_elimination" title="Common subexpression elimination">Common subexpression elimination</a></li>

<li><a href="Don't_repeat_yourself" title="Don't repeat yourself">Don't repeat yourself</a></li>

<li><a href="Duplicate_code" title="Duplicate code">Duplicate code</a></li>

<li><a href="Redundancy_(information_theory)" title="Redundancy (information theory)">Redundancy</a></li>

<li><a href="Code_refactoring" title="Code refactoring">Code refactoring</a></li>

<li><a href="Code_smell" title="Code smell">Code smell</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><a href="#cite_ref-1">^</a> <a rel="nofollow" class="external text" href="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.</a>

</li>

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This article is issued from <a class="external text" title="Last edited on 2025-06-24" href="https://en.wikipedia.org/wiki/?title=Redundant_code&oldid=1297154850">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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