Method getField2

Read a bit field starting at specified byte and bit, each numbered from 0. Bit numbering is from high to low, like this: getField bitIndex: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 Note that this is inverted with respect to the numbering scheme used in many GSM specs, which looks like this: GSM specs: 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 Note that some GSM specs use low-to-high and some use high-to-low numbering. G