_CAT_SET_HDR_SIZE
mem = nsets * _CAT_SET_HDR_SIZE + nmsgs * _CAT_MSG_HDR_SIZE + text_size;
hdrp->__msg_hdr_offset = nsets * _CAT_SET_HDR_SIZE;
hdrp->__msg_text_offset = nsets * _CAT_SET_HDR_SIZE +
hdr.__mem < hdr.__nsets * _CAT_SET_HDR_SIZE ||
+ _CAT_SET_HDR_SIZE * mid);