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Although the technique of branching using a branch table is most frequently used solely for the purpose of altering program flow – to jump to a program label that is an unconditional branch – the same technique can be used for other purposes.
[a] Branch (or branching, branched) may also refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction. Branch instructions are used to implement control flow in program loops and conditionals (i.e., executing a particular sequence of instructions only if certain conditions are ...
Continuation at a different statement (unconditional branch or jump) Executing a set of statements only if some condition is met (choice - i.e., conditional branch) Executing a set of statements zero or more times, until some condition is met (i.e., loop - the same as conditional branch)
Conditional branching statements allow a sequence of statements to be executed only if some condition is met. Otherwise, the statements are skipped and the execution sequence continues from the statement following them. Unconditional branching statements allow an execution sequence to be transferred to another part of a program.
A combination of state variables and structured control, notably an overall switch statement, can allow a subroutine to resume execution at an arbitrary point on subsequent calls, and is a structured alternative to goto statements in the absence of coroutines; this is a common idiom in C, for example.
Predicated instructions with different predicates can be mixed with each other and with unconditional code, allowing better instruction scheduling and so even better performance. Elimination of unnecessary branch instructions can make the execution of necessary branches, such as those that make up loops, faster by lessening the load on branch ...
c 1-c 6 – these six control bits specify the operands and computation to be performed by the ALU d 1-d 3 – these three bits specify the destination(s) for storing the current ALU output j 1-j 3 – these three bits specify an arithmetic branch condition, an unconditional branch (jump), or no branching
The control table entries are then much more similar to conditional statements in procedural languages but, crucially, without the actual (language dependent) conditional statements (i.e. instructions) being present (the generic code is physically in the interpreter that processes the table entries, not in the table itself – which simply ...