Search results
Results from the WOW.Com Content Network
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.
On modern processors, loop unrolling is often counterproductive, as the increased code size can cause more cache misses; cf. Duff's device. [1] The goal of loop unwinding is to increase a program's speed by reducing or eliminating instructions that control the loop, such as pointer arithmetic and "end of loop" tests on each iteration; [2 ...
The most common example of the correct use of a switch within a loop is an inversion of control such as an event handler. In event handler loops, the sequence of events is not known at compile-time, so the repeated switch is both necessary and correct (see event-driven programming , event loop and event-driven finite state machine ).
A protothread is a low-overhead mechanism for concurrent programming.. Protothreads function as stackless, lightweight threads, or coroutines, providing a blocking context cheaply using minimal memory per protothread (on the order of single bytes).
Simon Tatham's contribution, [38] based on Duff's device, is a notable example of the genre, and is the basis for Protothreads and similar implementations. [39] In addition to Duff's objections, [ 24 ] Tatham's own comments provide a frank evaluation of the limitations of this approach: "As far as I know, this is the worst piece of C hackery ...
The bandwidth on the loop is shared among all ports. Only two ports may communicate at a time on the loop. One port wins arbitration and may open one other port in either half or full duplex mode. A loop with two ports is valid and has the same physical topology as point-to-point, but still acts as a loop protocol-wise.
Iterative deepening prevents this loop and will reach the following nodes on the following depths, assuming it proceeds left-to-right as above: 0: A; 1: A, B, C, E (Iterative deepening has now seen C, when a conventional depth-first search did not.) 2: A, B, D, F, C, G, E, F (It still sees C, but that it came later.
Loop unswitching is a compiler optimization. It moves a conditional inside a loop outside of it by duplicating the loop's body, and placing a version of it inside each of the if and else clauses of the conditional. [1] This can improve the parallelization of the loop.