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Duff realized that to handle cases where count is not divisible by eight, the assembly programmer's technique of jumping into the loop body could be implemented by interlacing the structures of a switch statement and a loop, putting the switch's case labels at the points of the loop body that correspond to the remainder of count/8: [1]
Switch statements function somewhat similarly to the if statement used in programming languages like C/C++, C#, Visual Basic .NET, Java and exist in most high-level imperative programming languages such as Pascal, Ada, C/C++, C#, [1]: 374–375 Visual Basic .NET, Java, [2]: 157–167 and in many other types of language, using such keywords as ...
A form found in unstructured languages, mimicking a typical machine code instruction, would jump to (GOTO) a label or line number when the condition was met. IF..THEN..(ENDIF). Rather than being restricted to a jump, any simple statement, or nested block, could follow the THEN key keyword. This a structured form. IF..THEN..ELSE..(ENDIF). As ...
For example, one can write a fully recursive-nestable SWITCH–CASE–DEFAULT–ENDSWITCH statement using this macro facility. Because of the HLA macro facilities context-free design, these switch..case..default..endswitch statements can be nested, and the nested statements' emitted code will not conflict with the outside statements.
The switch parser function, coded as "#switch", selects the first matching branch in a list of choices, acting as a case statement. Each branch can be a value , an expression ( calculation ), or a template call, [ 1 ] evaluated and compared to match the value of the switch.
A loop-switch sequence [1] (also known as the for-case paradigm [2] or Anti-Duff's Device) is a programming antipattern where a clear set of steps is implemented as a switch-within-a-loop. The loop-switch sequence is a specific derivative of spaghetti code .
Examples of, and arguments for, Jump Tables via Function Pointer Arrays in C/C++; Example code generated by 'Switch/Case' branch table in C, versus IF/ELSE. Example code generated for array indexing if structure size is divisible by powers of 2 or otherwise. "Arrays of Pointers to Functions" by Nigel Jones
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).