OFFMASK
if ((in_file_off & OFFMASK) != 0 ||
(in_copy_len & OFFMASK) != 0)
src_rnd_size = (src_size + OFFMASK) & ~OFFMASK;
if ((args.in_dstoff & OFFMASK) != 0 ||
(args.in_xoff & OFFMASK) != 0 ||
(args.in_xlen & OFFMASK) != 0)
xlen &= ~OFFMASK;
args->out_xlen = (xlen + OFFMASK) & ~OFFMASK;