<s>
In	O
computer	B-General_Concept
science	I-General_Concept
and	O
information	O
theory	O
,	O
Tunstall	B-Algorithm
coding	I-Algorithm
is	O
a	O
form	O
of	O
entropy	B-Algorithm
coding	I-Algorithm
used	O
for	O
lossless	B-Algorithm
data	I-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Tunstall	B-Algorithm
coding	I-Algorithm
was	O
the	O
subject	O
of	O
Brian	O
Parker	O
Tunstall	O
's	O
PhD	O
thesis	O
in	O
1967	O
,	O
while	O
at	O
Georgia	O
Institute	O
of	O
Technology	O
.	O
</s>
<s>
Its	O
design	O
is	O
a	O
precursor	O
to	O
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
.	O
</s>
<s>
Unlike	O
variable-length	B-Algorithm
codes	I-Algorithm
,	O
which	O
include	O
Huffman	B-General_Concept
and	O
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
coding	I-Algorithm
,	O
</s>
<s>
Tunstall	B-Algorithm
coding	I-Algorithm
is	O
a	O
code	O
which	O
maps	O
source	O
symbols	O
to	O
a	O
fixed	O
number	O
of	O
bits	O
.	O
</s>
<s>
Both	O
Tunstall	O
codes	O
and	O
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
codes	O
represent	O
variable-length	O
words	O
by	O
fixed-length	O
codes	O
.	O
</s>
<s>
Unlike	O
typical	O
set	O
encoding	O
,	O
Tunstall	B-Algorithm
coding	I-Algorithm
parses	O
a	O
stochastic	O
source	O
with	O
codewords	O
of	O
variable	O
length	O
.	O
</s>
<s>
Tunstall	B-Algorithm
coding	I-Algorithm
requires	O
the	O
algorithm	O
to	O
know	O
,	O
prior	O
to	O
the	O
parsing	O
operation	O
,	O
what	O
the	O
distribution	O
of	O
probabilities	O
for	O
each	O
letter	O
of	O
the	O
alphabet	O
is	O
.	O
</s>
<s>
This	O
issue	O
is	O
shared	O
with	O
Huffman	B-General_Concept
coding	I-General_Concept
.	O
</s>
<s>
Its	O
requiring	O
a	O
fixed-length	O
block	O
output	O
makes	O
it	O
lesser	O
than	O
Lempel	B-Algorithm
–	I-Algorithm
Ziv	I-Algorithm
,	O
which	O
has	O
a	O
similar	O
dictionary-based	O
design	O
,	O
but	O
with	O
a	O
variable-sized	O
block	O
output	O
.	O
</s>
