| 摘要 |
A method and apparatus for providing program loop control in a data processor employs a special purpose instruction that substantially reduces the program overhead associated with conditional branching at the end of a program loop. The instruction first compares a loop counter with a decrement value. If the loop counter has counted down, a loop condition code, which is stored in a dedicated register bit, is cleared. Otherwise, the loop condition code remains set to indicate that further iterations of the loop are required. The decremented value of the loop counter is then stored in a loop counter register. In parallel with decrementing of the loop counter, a conditional branch is executed based on the value of the loop condition code set in the immediately previous iteration of the loop. If the loop condition code is cleared, i.e. if the loop has been completed, program control proceeds to the instruction following the loop after execution of the next instruction in sequence. conversely, if the loop condition code is set, program control returns to the branch address, i.e. the beginning of the loop, after execution of the next instruction in sequence. All of the operations of the present invention are performed within a single instruction cycle.
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