computer programming Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of proc ...

, redundant code is

source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...

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 Execution (computing), execute. It is one component of software, which also includes software documentation, documentation and other intangibl ...

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 The term dead code has multiple definitions. Some use the term to refer to code (i.e. instructions in memory) which can never be executed at run-time. In some areas of computer programming, dead code is a section in the source code of a program whi ...

). 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 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, person, physical countable object (or class thereof), or physical mass ...

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 (CPP) is a text file processor that is used with C, C++ and other programming tools. The preprocessor provides for file inclusion (often header files), macro expansion, conditional compilation, and line control. Although ...

, 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