<s>
In	O
computer	O
performance	O
,	O
the	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
is	O
the	O
number	O
of	O
machine	B-Language
code	I-Language
instructions	O
required	O
to	O
execute	O
a	O
section	O
of	O
a	O
computer	B-Application
program	I-Application
.	O
</s>
<s>
The	O
total	O
path	O
length	O
for	O
the	O
entire	O
program	O
could	O
be	O
deemed	O
a	O
measure	O
of	O
the	O
algorithm	O
's	O
performance	O
on	O
a	O
particular	O
computer	B-Architecture
hardware	I-Architecture
.	O
</s>
<s>
When	O
executing	O
a	O
benchmark	O
program	O
,	O
most	O
of	O
the	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
is	O
typically	O
inside	O
the	O
program	O
's	O
inner	O
loop	O
.	O
</s>
<s>
Before	O
the	O
introduction	O
of	O
caches	B-General_Concept
,	O
the	O
path	O
length	O
was	O
an	O
approximation	O
of	O
running	O
time	O
,	O
but	O
in	O
modern	O
CPUs	O
with	O
caches	B-General_Concept
,	O
it	O
can	O
be	O
a	O
much	O
worse	O
approximation	O
,	O
with	O
some	O
load	O
instructions	O
taking	O
hundreds	O
of	O
cycles	O
when	O
the	O
data	O
is	O
not	O
in	O
cache	B-General_Concept
,	O
or	O
orders	O
of	O
magnitude	O
faster	O
when	O
in	O
cache	B-General_Concept
(	O
even	O
the	O
same	O
instruction	O
in	O
another	O
round	O
in	O
a	O
loop	O
)	O
.	O
</s>
<s>
Since	O
there	O
is	O
,	O
typically	O
,	O
a	O
one-to-one	O
relationship	O
between	O
assembly	B-Language
instructions	O
and	O
machine	B-Language
instructions	I-Language
,	O
the	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
is	O
frequently	O
taken	O
as	O
the	O
number	O
of	O
assembly	B-Language
instructions	O
required	O
to	O
perform	O
a	O
function	O
or	O
particular	O
section	O
of	O
code	O
.	O
</s>
<s>
Performing	O
a	O
simple	O
table	B-Data_Structure
lookup	I-Data_Structure
on	O
an	O
unsorted	B-Algorithm
list	I-Algorithm
of	O
1,000	O
entries	O
might	O
require	O
perhaps	O
2,000	O
machine	B-Language
instructions	I-Language
(	O
on	O
average	O
,	O
assuming	O
uniform	O
distribution	O
of	O
input	O
values	O
)	O
,	O
while	O
performing	O
the	O
same	O
lookup	B-Data_Structure
on	O
a	O
sorted	B-Algorithm
list	I-Algorithm
using	O
a	O
binary	O
search	O
algorithm	O
might	O
require	O
only	O
about	O
40	O
machine	B-Language
instructions	I-Language
,	O
a	O
very	O
considerable	O
saving	O
.	O
</s>
<s>
Expressed	O
in	O
terms	O
of	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
,	O
this	O
metric	O
would	O
be	O
reduced	O
in	O
this	O
instance	O
by	O
a	O
massive	O
factor	O
of	O
50	O
a	O
reason	O
why	O
actual	O
instruction	O
timings	O
might	O
be	O
a	O
secondary	O
consideration	O
compared	O
to	O
a	O
good	O
choice	O
of	O
algorithm	O
requiring	O
a	O
shorter	O
path	O
length	O
.	O
</s>
<s>
The	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
of	O
an	O
assembly	B-Language
language	I-Language
program	O
is	O
generally	O
vastly	O
different	O
than	O
the	O
number	O
of	O
source	O
lines	O
of	O
code	O
for	O
that	O
program	O
,	O
because	O
the	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
includes	O
only	O
code	O
in	O
the	O
executed	O
control	O
flow	O
for	O
the	O
given	O
input	O
and	O
does	O
not	O
include	O
code	O
that	O
is	O
not	O
relevant	O
for	O
the	O
particular	O
input	O
,	O
or	O
unreachable	O
code	O
.	O
</s>
<s>
Since	O
one	O
statement	O
written	O
in	O
a	O
high-level	O
language	O
can	O
produce	O
multiple	O
machine	B-Language
instructions	I-Language
of	O
variable	O
number	O
,	O
it	O
is	O
not	O
always	O
possible	O
to	O
determine	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
without	O
,	O
for	O
example	O
,	O
an	O
instruction	B-Application
set	I-Application
simulator	I-Application
that	O
can	O
count	O
the	O
number	O
of	O
'	O
executed	O
 '	O
instructions	O
during	O
simulation	O
.	O
</s>
<s>
If	O
the	O
high-level	O
language	O
supports	O
and	O
optionally	O
produces	O
an	O
'	O
assembly	B-Language
list	O
 '	O
,	O
it	O
is	O
sometimes	O
possible	O
to	O
estimate	O
the	O
instruction	B-General_Concept
path	I-General_Concept
length	I-General_Concept
by	O
examining	O
this	O
list	O
.	O
</s>
<s>
From	O
the	O
above	O
,	O
it	O
can	O
be	O
realized	O
that	O
knowledge	O
of	O
instruction	B-General_Concept
path	I-General_Concept
lengths	I-General_Concept
can	O
be	O
used	O
:	O
</s>
