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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.
DOALL parallelism exists when statements within a loop can be executed independently (situations where there is no loop-carried dependence). [1] For example, the following code does not read from the array a, and does not update the arrays b, c. No iterations have a dependence on any other iteration.
If the statements in the loop are independent of each other (i.e. where statements that occur earlier in the loop do not affect statements that follow them), the statements can potentially be executed in parallel. Can be implemented dynamically if the number of array elements is unknown at compile time (as in Duff's device).
A conditional loop has the potential to become an infinite loop when nothing in the loop's body can affect the outcome of the loop's conditional statement. 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 ...
Fortran's equivalent of the for loop is the DO loop, using the keyword do instead of for, The syntax of Fortran's DO loop is: DO label counter = first , last , step statements label statement The following two examples behave equivalently to the three argument for-loop in other languages, initializing the counter variable to 1, incrementing by ...
Do while loops check the condition after the block of code is executed. This control structure can be known as a post-test loop. This means the do-while loop is an exit-condition loop. However a while loop will test the condition before the code within the block is executed.
The loop-switch sequence is a specific derivative of spaghetti code. It is not necessarily an antipattern to use a switch statement within a loop—it is only considered incorrect when used to model a known sequence of steps. The most common example of the correct use of a switch within a loop is an inversion of control such as
If xxx1 is omitted, we get a loop with the test at the top (a traditional while loop). If xxx2 is omitted, we get a loop with the test at the bottom, equivalent to a do while loop in many languages. 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 ...