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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.
Switch expressions are introduced in Java SE 12, 19 March 2019, as a preview feature. Here a whole switch expression can be used to return a value. There is also a new form of case label, case L-> where the right-hand-side is a single expression. This also prevents fall through and requires that cases are exhaustive.
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
This pointer function method can result in saving one machine instruction, and avoids the indirect jump (to one of the branch instructions). The resulting list of pointers to functions is almost identical to direct threaded code, and is conceptually similar to a control table. The actual method used to implement a branch table is usually based on:
ARM's Thumb instruction set (1994) dropped conditional execution to reduce the size of instructions so they could fit in 16 bits, but its successor, Thumb-2 (2003) overcame this problem by using a special instruction which has no effect other than to supply predicates for the following four instructions. The 64-bit instruction set introduced in ...
C = A+B needs four instructions. 3-operand, allowing better reuse of data: [11] CISC — It becomes either a single instruction: add a,b,c. C = A+B needs one instruction. CISC — Or, on machines limited to two memory operands per instruction, move a,reg1; add reg1,b,c; C = A+B needs two instructions.
In computer architecture, the test-and-set CPU instruction (or instruction sequence) is designed to implement mutual exclusion in multiprocessor environments. Although a correct lock can be implemented with test-and-set, the test and test-and-set optimization lowers resource contention caused by bus locking, especially cache coherency protocol overhead on contended locks.
switch <uint32, int32, int32 (t1..tN)> Jump to one of n values. Base instruction 0xFE 0x14 tail. Subsequent call terminates current method. Prefix to instruction 0x7A throw: Throw an exception. Object model instruction 0xFE 0x12 unaligned. (alignment) Subsequent pointer instruction might be unaligned. Prefix to instruction 0x79 unbox <valuetype>