Multiway Branch

Multiway branch is the change to a program's control flow based upon a value matching a selected criteria. It is a form of conditional statement. A multiway branch is often the most efficient method of passing control to one of a set of program labels, especially if an index has been created beforehand from the raw data.

Examples

* Branch table
* Switch statement - see also alternatives below
* Multiple dispatch - where a subroutine is invoked and a return is made

Alternatives

A multiway branch can, frequently, be replaced with an efficient indexed table lookup (using the data value itself or a calculated derivative of the data value, as the index of an array)

"''...the implementation of a switch statement has been equated with that of a multiway branch. However, for many uses of the switch statement in real code, it is possible to avoid branching altogether and replace the switch with one or more table look-ups. For example,the Has30Days example resented earliercan be implemented as the following: example''"A Superoptimizer Analysis of Multiway Branch Code Generation"
by Roger Anthony Sayle

switch (x)

can be replaced, using a "safe-hashing" technique, with -

unsigned int t = x , 2;
switch (t)

or it can be replaced, using an index mapping table lookup, with -

x %= 12; /* to ensure x is in range 0-11*/
static const int T 2=; /* 0-based table 'if 30 days =1,else 0' */
return T /* return with boolean 1 = true, 0=false */

(in view of the simplicity of the latter case, it would be preferable to implement it in-line, since the overhead of using a function call may be greater than the indexed lookup itself.)

Quotations

See also

*Conditional (programming)
*Lookup table

References

{{Reflist

External links

Coding Multiway Branches Using Customized Hash functions
by H. G. Dietz
Learning Python
By Mark Lutz
Programming in C++
By Nell B. Dale, Chip Weems
A Superoptimizer Analysis of Multiway Branch Code Generation
by Roger Anthony Sayle

Conditional constructs