log2_comm_size    837 ompi/mca/coll/base/coll_base_reduce_scatter_block.c     int log2_comm_size = opal_cube_dim(comm_size);
log2_comm_size    841 ompi/mca/coll/base/coll_base_reduce_scatter_block.c         char *dst = psend + (ptrdiff_t)ompi_mirror_perm(i, log2_comm_size) * extent * rcount;