machine level branch is the return instruction. This "pops" a return address off the stack and loads it into the PC register, thus returning control to the calling routine. Return instructions may also be conditionally executed. This description pertains to ordinary practice; however, the machine programmer has considerable powers to manipulate the return address on the stack, and so redirect program execution in any number of different ways. Depending on the processor, jump and call instructions may alter the contents of the PC register in different ways. An absolute address may be loaded, or the current contents of the PC may have some value (or displacement) added or subtracted from its current value, making the destination address relative to the current place in the program. The source of the displacement value may vary, such as an immediate value embedded within the instruction, or the contents of a processor register or memory location, or the contents of some location added to an index value. The term branch can also be used when referring to programs in high-level programming languages. In these 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 a different instruction sequence. If the algorithm requires a conditional branch, the GOTO (or GOSUB subroutine call) is preceded by an IF-THEN statement specifying the condition(s). All high level languages support algorithms that can re-use code as a loop, a control structure that repeats a sequence of instructions until some condition is satisfied that causes the loop to terminate. Loops also qualify as branch instructions. At the machine level, loops are implemented as ordinary conditional jumps that redirect execution to repeating code. In CPUs with flag registers, an earlier instruction sets a condition in the flag register. The earlier instruction may be arithmetic, or a logic instruction. It is often close to the branch, though not necessarily the instruction immediately before the branch. The stored condition is then used in a branch such as jump if overflow-flag set. This temporary information is often stored in a flag register but may also be located elsewhere. A flag register design is simple in slower, simple computers. In fast computers a flag register can place a bottleneck on speed, because instructions that could otherwise operate in