implement Attrhash, Attrindex; include "sys.m";	sys: Sys; include "bufio.m";	bufio: Bufio; include "attrdb.m"; init(): string{	sys = load Sys Sys->PATH;	bufio = load Bufio Bufio->PATH;	if(bufio == nil)		return sys->sprint("can't load %s: %r", Bufio->PATH);	return nil;} attrindex(): Attrindex{	return load Attrindex "$self";} Index.open(dbf: Attrdb->Dbf, attr: string, fd: ref Sys->FD): ref Index{	(ok, d) := sys->fstat(fd);	if(ok < 0 || dbf.dir == nil || dbf.dir.mtime > d.mtime)		return nil;	length := int d.length;	if(length < NDBHLEN)		return nil;	buf := array[length] of byte;	if(sys->read(fd, buf, len buf) != len buf)		return nil;	mtime := get4(buf);	if(mtime != dbf.dir.mtime)		return nil;	size := get3(buf[4:]);	return ref Index(fd, attr, d.mtime, size, buf[8:]);} #Index.firstoff(ind: self ref Index, val: string): ref Attrdb->Dbptr#{#	o := hash(val, ind.size)*NDBPLEN;#	p := get3(tab[o:]);#	if(p == NDBNAP)#		return nil;#	if((p & NDBCHAIN) == 0)#		return ref Attrdb.Direct(p);#	p &= ~NDBCHAIN;#	return ref Attrdb.Hash(get3(tab[p:]), get3(tab[p+NDBPLEN:]));#} #Index.nextoff(ind: self ref Index, val: string, ptr: ref Attrdb->Dbptr): (int, ref Attrdb->Dbptr)#{#	pick p := ptr {#	Hash =>#		o := get3(tab[p.current:]);#		if((o & NDBCHAIN) == 0)#			return (o, ref Attrdb.Direct(p.next));#		o &= ~NDBCHAIN;#		o1 := get3(tab[o:]);#		o2 := get3(tab[o+NDBPLEN:]);#		 #	o := hash(val, ind.size)*NDBPLEN;#	p := get3(tab[o:]);#	if(p == NDBNAP)#		return nil;#	for(; (p := get3(tab[o:])) != NDBNAP; o = p & ~NDBCHAIN)#		if((p & NDBCHAIN) == 0){#			put3(tab[o:], chain | NDBCHAIN);#			put3(tab[chain:], p);#			put3(tab[chain+NDBPLEN:], offset);#			return chain+2*NDBPLEN;#		}#	return nil;#} ## this must be the same hash function used by Plan 9's ndb#hash(s: string, hlen: int): int{	h := 0;	for(i := 0; i < len s; i++)		if(s[i] >= 16r80){			# could optimise by calculating utf ourselves			a := array of byte s;			for(i=0; i<len a; i++)				h = (h*13) + int a[i] - 'a';			break;		}else			h = (h*13) + s[i]-'a';	if(h < 0)		return int((big h & big 16rFFFFFFFF)%big hlen);	return h%hlen;} get3(a: array of byte): int{	return (int a[2]<<16) | (int a[1]<<8) | int a[0];} get4(a: array of byte): int{	return (int a[3]<<24) | (int a[2]<<16) | (int a[1]<<8) | int a[0];}