PTOB
out = s->blkbuf + PTOB(s->nout);
out = dpage + PTOB(nout);
#define DATAOFF(p) (corehdr.dump_data + PTOB(p))
Pwrite(corefd, buf, PTOB(np), DATAOFF(pgnum));
out = s->blkbuf + PTOB(s->nout);