<s>
Index	B-Data_Structure
mapping	I-Data_Structure
(	O
or	O
direct	O
addressing	O
,	O
or	O
a	O
trivial	B-Data_Structure
hash	I-Data_Structure
function	I-Data_Structure
)	O
in	O
computer	B-General_Concept
science	I-General_Concept
describes	O
using	O
an	O
array	B-Data_Structure
,	O
in	O
which	O
each	O
position	O
corresponds	O
to	O
a	O
key	O
in	O
the	O
universe	O
of	O
possible	O
values	O
.	O
</s>
<s>
The	O
technique	O
is	O
most	O
effective	O
when	O
the	O
universe	O
of	O
keys	O
is	O
reasonably	O
small	O
,	O
such	O
that	O
allocating	B-General_Concept
an	O
array	B-Data_Structure
with	O
one	O
position	O
for	O
every	O
possible	O
key	O
is	O
affordable	O
.	O
</s>
<s>
Its	O
effectiveness	O
comes	O
from	O
the	O
fact	O
that	O
an	O
arbitrary	O
position	O
in	O
an	O
array	B-Data_Structure
can	O
be	O
examined	O
in	O
constant	O
time	O
.	O
</s>
<s>
A	O
trivial	B-Data_Structure
hash	I-Data_Structure
function	I-Data_Structure
is	O
a	O
suitable	O
choice	O
when	O
such	O
data	O
needs	O
to	O
act	O
as	O
a	O
lookup	B-Data_Structure
key	O
.	O
</s>
<s>
Using	O
a	O
trivial	B-Data_Structure
hash	I-Data_Structure
function	I-Data_Structure
,	O
in	O
a	O
non-iterative	O
table	B-Data_Structure
lookup	I-Data_Structure
,	O
can	O
eliminate	O
conditional	O
testing	O
and	O
branching	O
completely	O
,	O
reducing	O
the	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
of	O
a	O
computer	O
program	O
.	O
</s>
<s>
Which	O
can	O
be	O
replaced	O
with	O
a	O
table	B-Data_Structure
lookup	I-Data_Structure
:	O
</s>
