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#include <u.h>
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#include <libc.h>
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#include <bio.h>
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#include <ndb.h>
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/*
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 *  make the hash table completely in memory and then write as a file
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 */
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uchar *ht;
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ulong hlen;
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Ndb *db;
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ulong nextchain;
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char*
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syserr(void)
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{
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	static char buf[ERRMAX];
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	errstr(buf, sizeof buf);
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	return buf;
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}
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void
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enter(char *val, ulong dboff)
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{
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	ulong h;
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	uchar *last;
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	ulong ptr;
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	h = ndbhash(val, hlen);
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	h *= NDBPLEN;
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	last = &ht[h];
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	ptr = NDBGETP(last);
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	if(ptr == NDBNAP){
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		NDBPUTP(dboff, last);
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		return;
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	}
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	if(ptr & NDBCHAIN){
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		/* walk the chain to the last entry */
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		for(;;){
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			ptr &= ~NDBCHAIN;
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			last = &ht[ptr+NDBPLEN];
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			ptr = NDBGETP(last);
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			if(ptr == NDBNAP){
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				NDBPUTP(dboff, last);
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				return;
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			}
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			if(!(ptr & NDBCHAIN)){
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				NDBPUTP(nextchain|NDBCHAIN, last);
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				break;
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			}
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		}
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	} else
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		NDBPUTP(nextchain|NDBCHAIN, last);
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	/* add a chained entry */
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	NDBPUTP(ptr, &ht[nextchain]);
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	NDBPUTP(dboff, &ht[nextchain + NDBPLEN]);
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	nextchain += 2*NDBPLEN;
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}
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uchar nbuf[16*1024];
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void
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main(int argc, char **argv)
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{
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	Ndbtuple *t, *nt;
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	int n;
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	Dir *d;
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	uchar buf[8];
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	char file[128];
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	int fd;
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	ulong off;
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	uchar *p;
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	if(argc != 3){
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		fprint(2, "usage: mkhash file attribute\n");
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		exits("usage");
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	}
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	db = ndbopen(argv[1]);
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	if(db == 0){
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		fprint(2, "mkhash: can't open %s\n", argv[1]);
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		exits(syserr());
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	}
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	/* try a bigger than normal buffer */
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	Binits(&db->b, Bfildes(&db->b), OREAD, nbuf, sizeof(nbuf));
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	/* count entries to calculate hash size */
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	n = 0;
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	while(nt = ndbparse(db)){
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		for(t = nt; t; t = t->entry){
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			if(strcmp(t->attr, argv[2]) == 0)
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				n++;
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		}
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		ndbfree(nt);
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	}
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	/* allocate an array large enough for worst case */
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	hlen = 2*n+1;
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	n = hlen*NDBPLEN + hlen*2*NDBPLEN;
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	ht = mallocz(n, 1);
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	if(ht == 0){
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		fprint(2, "mkhash: not enough memory\n");
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		exits(syserr());
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	}
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	for(p = ht; p < &ht[n]; p += NDBPLEN)
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		NDBPUTP(NDBNAP, p);
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	nextchain = hlen*NDBPLEN;
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	/* create the in core hash table */
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	Bseek(&db->b, 0, 0);
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	off = 0;
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	while(nt = ndbparse(db)){
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		for(t = nt; t; t = t->entry){
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			if(strcmp(t->attr, argv[2]) == 0)
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				enter(t->val, off);
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		}
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		ndbfree(nt);
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		off = Boffset(&db->b);
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	}
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	/* create the hash file */
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	snprint(file, sizeof(file), "%s.%s", argv[1], argv[2]);
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	fd = create(file, ORDWR, 0664);
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	if(fd < 0){
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		fprint(2, "mkhash: can't create %s\n", file);
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		exits(syserr());
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	}
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	NDBPUTUL(db->mtime, buf);
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	NDBPUTUL(hlen, buf+NDBULLEN);
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	if(write(fd, buf, NDBHLEN) != NDBHLEN){
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		fprint(2, "mkhash: writing %s\n", file);
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		exits(syserr());
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	}
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	if(write(fd, ht, nextchain) != nextchain){
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		fprint(2, "mkhash: writing %s\n", file);
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		exits(syserr());
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	}
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	close(fd);
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	/* make sure file didn't change while we were making the hash */
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	d = dirstat(argv[1]);
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	if(d == nil || d->qid.path != db->qid.path
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	   || d->qid.vers != db->qid.vers){
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		fprint(2, "mkhash: %s changed underfoot\n", argv[1]);
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		remove(file);
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		exits("changed");
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	}
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	exits(0);
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}