1. A processor that, within the processor, stores one or more index values in a SIMD register: wherein each of the one or more index values represent a position of a bit that is set to one in a bit vector; wherein bits in the bit vector are contiguous; wherein the processor is configured to respond to one or more instructions by: determining whether each bit in the bit vector is set to one; storing an index value in the SIMD register for each bit determined to be set to one.