Conditional branch

A branch is an instruction in a computer program that can cause a computer to begin executing a different instruction sequence and thus deviate from its default behavior of executing instructions in order.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. A branch instruction can be either an unconditional branch, which always results in branching, or a conditional branch, which may or may not cause branching, depending on some condition. 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 satisfied).

Mechanically, a branch instruction can change the program counter of a CPU. The program counter is the memory address of the next instruction. Therefore, a branch can cause the CPU to begin fetching its instructions from a different sequence of memory cells.

When a branch is taken, the CPU's program counter is set to the argument of the jump instruction. So, the next instruction becomes the instruction at that address in memory. Therefore, the flow of control changes.

When a branch is not taken, the CPU's program counter is unchanged. Therefore, the next instruction executed is the instruction after the branch instruction. Therefore, the flow of control is unchanged.

The term branch can be used when referring to programs in high level languages as well as program written in machine code or assembly language. In high-level programming languages, branches usually take the form of conditional statements of various forms that encapsulate the instruction sequence that will be executed if the conditions are satisfied. Unconditional branch instructions such as GOTO are used to unconditionally "jump" to (begin execution of) a different instruction sequence.

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