bitv_chunk
static unsigned bitv_chunk(const bitv *bv, unsigned limbit, unsigned lobit);
crc(&csum, bitv_chunk(allbits, limbit, limbit - 5));
*code++ = Alphabet[bitv_chunk(allbits, limbit, limbit - 5)];
ocsum = bitv_chunk(allbits, infop->csumbits, 0);
crc(&csum, bitv_chunk(allbits, limbit, limbit - 5));
bitv_chunk(allbits, limbit, limbit - 1));