> I am working with some IPv6 addresses that are 128 bits long. > The input to the program is an ip name or address and the > number of high bits that I need to use for a compare against > another ip address.
> So, I want to create run time routine to build the a > 16 byte 'and' bit field based on the input number of bits. > (I will then 'and' both addresses and then use a simple CLC.) There is no double 64 bit (that is, 128 bit) shift instruction as far as I know. Most obvious is to store the bits in some number of bytes, halfwords, words, or doublewords. Then, based on the shift amount, fill some with all ones, and use a shift instruction (or smaller table) for the boundary case. I would probably choose words. Using shift and mask, split the shift amount into 32's and a remainder (or use Divide). For bytes in memory, EX an MVC, or a loop of MVI, to fill the high bytes. Use a table of bytes to IC and STC the boundary byte. -- glen
