[openib-general] Re: [PATCH] Fix ib_pack/unpack for 64 bits

[Roland Dreier]

    Hal> It fixes 64 bit sizes (at least on 32 bit machines). The
    Hal> problem was with the mask computation when size_bits = 64.

    Hal> mask = cpu_to_be64(((1ull << desc[i].size_bits) - 1) << shift);

    Hal> yielded a mask of 0 (for size_bits 64 and shift of 0). The 32
    Hal> bit mask computation relies on the 33rd bit. In this case,
    Hal> shifting the 1 64 bits does not put it in the 65th bit which
    Hal> is needed for proper mask calculation.

Hmm, is there anywhere that actually sets size_bits to 64?

It's odd that you saw the expession end up as 0.  It seems that on every
system I have, 1ull << 64 is 0, and 0 - 1 == -1 == 0xffffffffffffffff.
So although it isn't correct C, it should work.

It is true that left shifting a 64-bit type by 64 bits is undefined
according to standard C.  I'll fix this up.

 - R.