Accelerating traceback on a signal processor

A method executed by an instruction set on a processor is described. The method includes providing a tbbit instruction, inputting a first index for the tbbit instruction, loading a second value for the tbbit instruction, wherein the second value comprises at least 2b bits, using selected b bits of the first index to select at least one target bit in the loaded second value, shifting the target bit into the bottom of the first index, and computing a second index based on the shifting of the target bit into the bottom of the first index. Other methods and variations are also described.