computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as ana ...

, redundant code is

source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the wo ...

or compiled code in a

computer program A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...

that is unnecessary, such as: * recomputing a value that has previously been calculatedDebray, 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> and is still available, * code that is never executed (known as

unreachable code In computer programming, unreachable code is part of the source code of a program which can never be executed because there exists no control flow path to the code from the rest of the program. Unreachable code is sometimes also called ''dead code' ...

), * code which is executed but has no external effect (e.g., does not change the output produced by a program; known as dead code). A NOP instruction might be considered to be redundant code that has been explicitly inserted to pad out the instruction stream or introduce a time delay, for example to create a

timing loop Timing is the tracking or planning of the spacing of events in time. It may refer to: * Timekeeping, the process of measuring the passage of time * Synchronization, controlling the timing of a process relative to another process * Time metrolo ...

by "wasting time".

Identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, where the "object" or class may be an idea, physical countable object (or class thereof), or physical noncountable ...

s that are declared, but never referenced, are termed redundant declarations.

Examples

The following examples are in C. int foo(int iX) The second iX*2 expression is redundant code and can be replaced by a reference to the variable iY. Alternatively, the definition int iY = iX*2 can instead be removed. Consider: #define min(A,B) ((A)<(B)?(A):(B)) int shorter_magnitude(int u1, int v1, int u2, int v2) As a consequence of using the

C preprocessor The C preprocessor is the macro preprocessor for the C, Objective-C and C++ computer programming languages. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control ...

, the compiler will only see the expanded form: int shorter_magnitude(int u1, int v1, int u2, int v2) 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: #define max(A,B) ((A)>(B)?(A):(B)) int random(int cutoff, int range) 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.

References

{{Reflist Compiler optimizations Software anomalies Source code

Examples

See also

References