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In the C programming language, Duff's device is a way of manually implementing loop unrolling by interleaving two syntactic constructs of C: the do-while loop and a switch statement. Its discovery is credited to Tom Duff in November 1983, when Duff was working for Lucasfilm and used it to speed up a real-time animation program.
In many computer programming languages, a do while loop is a control flow statement that executes a block of code and then either repeats the block or exits the loop depending on a given boolean condition. The do while construct consists of a process symbol and a condition. First the code within the block is executed.
Loop unrolling, also known as loop unwinding, is a loop transformation technique that attempts to optimize a program's execution speed at the expense of its binary size, which is an approach known as space–time tradeoff. The transformation can be undertaken manually by the programmer or by an optimizing compiler.
Compare this with the do while loop, which tests the condition/expression after the loop has executed. For example, in the languages C, Java, C#, [2] Objective-C, and C++, (which use the same syntax in this case), the code fragment
If while is omitted, we get an infinite loop. The construction here can be thought of as a do loop with the while check in the middle. Hence this single construction can replace several constructions in most programming languages. Languages lacking this construct generally emulate it using an equivalent infinite-loop-with-break idiom: while ...
However, infinite loops can sometimes be used purposely, often with an exit from the loop built into the loop implementation for every computer language, but many share the same basic structure and/or concept. The While loop and the For loop are the two most common types of conditional loops in most programming languages.
C program source text is free-form code. Semicolons terminate statements, while curly braces are used to group statements into blocks. The C language also exhibits the following characteristics: The language has a small, fixed number of keywords, including a full set of control flow primitives: if/else, for, do/while, while, and switch.
LOOP is a simple register language that precisely captures the primitive recursive functions. [1] The language is derived from the counter-machine model.Like the counter machines the LOOP language comprises a set of one or more unbounded registers, each of which can hold a single non-negative integer.