<s>
Extendible	B-Algorithm
hashing	I-Algorithm
is	O
a	O
type	O
of	O
hash	B-Error_Name
system	O
which	O
treats	O
a	O
hash	B-Error_Name
as	O
a	O
bit	O
string	O
and	O
uses	O
a	O
trie	B-General_Concept
for	O
bucket	O
lookup	O
.	O
</s>
<s>
This	O
means	O
that	O
time-sensitive	O
applications	O
are	O
less	O
affected	O
by	O
table	O
growth	O
than	O
by	O
standard	O
full-table	O
rehashes	B-Algorithm
.	O
</s>
<s>
Extendible	B-Algorithm
hashing	I-Algorithm
was	O
described	O
by	O
Ronald	O
Fagin	O
in	O
1979	O
.	O
</s>
<s>
Practically	O
all	O
modern	O
filesystems	O
use	O
either	O
extendible	B-Algorithm
hashing	I-Algorithm
or	O
B-trees	B-Architecture
.	O
</s>
<s>
In	O
particular	O
,	O
the	O
Global	B-Application
File	I-Application
System	I-Application
,	O
ZFS	B-Application
,	O
and	O
the	O
SpadFS	O
filesystem	O
use	O
extendible	B-Algorithm
hashing	I-Algorithm
.	O
</s>
<s>
Assume	O
that	O
the	O
hash	B-Error_Name
function	I-Error_Name
returns	O
a	O
string	O
of	O
bits	O
.	O
</s>
<s>
The	O
first	O
i	O
bits	O
of	O
each	O
string	O
will	O
be	O
used	O
as	O
indices	O
to	O
figure	O
out	O
where	O
they	O
will	O
go	O
in	O
the	O
"	O
directory	O
"	O
(	O
hash	B-Algorithm
table	I-Algorithm
)	O
.	O
</s>
<s>
Examining	O
the	O
initial	O
case	O
of	O
an	O
extendible	O
hash	B-Error_Name
structure	O
,	O
if	O
each	O
directory	O
entry	O
points	O
to	O
one	O
bucket	O
,	O
then	O
the	O
local	O
depth	O
should	O
be	O
equal	O
to	O
the	O
global	O
depth	O
.	O
</s>
<s>
Below	O
is	O
the	O
extendible	B-Algorithm
hashing	I-Algorithm
algorithm	O
in	O
Python	B-Language
,	O
with	O
the	O
disc	O
block	O
/	O
memory	O
page	O
association	O
,	O
caching	O
and	O
consistency	O
issues	O
removed	O
.	O
</s>
