What is 8 bit fast indexing of arrays? The internal PIC hardware (on the 14 bit PIC cores) is restricted to an 8 bit indirection register. Under certain conditions the XCSB compiler treats indexing as an 8 bit function rather than a 16 bit function which ends in the most significant 8 bits being discarded. This reduces runtime calculations and greatly improving execution speed at the expense of a more complex compiler.