= Things you should know about Lua's performance =

This wiki is a result of some lua performance tests (the widget is included with ca sandbox).
[[BR]][[BR]][[BR]]

== TEST 1: localize ==
Code:
{{{
#!lua
local min = math.min
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">normal way: 0.719 (158%)</font><br>
<font color="green" style="font-weight:bold">localized: 0.453 (100%)</font>
</div>
}}}
Conclusion:
{{{
-> Yeah, we should localize all used funtions.
}}}

== TEST 2: localized class-methods (with only 3 accesses!) ==
Code1:
{{{
#!lua
for i=1,1000000 do
local x = class.test()
local y = class.test()
local z = class.test()
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
local test = class.test
local x = test()
local y = test()
local z = test()
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
normal way: 1.203 (102%)<br>
localized: 1.172 (100%)
</div>
}}}
Conclusion:
{{{
-> No, it isn't faster to localize a class method IN the function call.
}}}

== TEST 3: unpack a table ==
Code1:
{{{
#!lua
for i=1,1000000 do
local x = min( a[1],a[2],a[3],a[4] )
end
}}}
Code2:
{{{
#!lua
local unpack = unpack
for i=1,1000000 do
local x = min( unpack(a) )
end
}}}
Code3:
{{{
#!lua
local function unpack4(a)
return a[1],a[2],a[3],a[4]
end
for i=1,1000000 do
local x = min( unpack4(a) )
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="green" style="font-weight:bold">with [ ]: 0.485 (100%)</font><br>
<font color="red" style="font-weight:bold">unpack(): 1.093 (225%)</font><br>
custom unpack4: 0.641 (131%)
</div>
}}}
Conclusion:
{{{
-> Don't use unpack() in time critical code!
}}}

== TEST 4: determine maximum and set it ('>' vs. max) ==
Code1:
{{{
#!lua
local max = math.max
for i=1,1000000 do
x = max(random(cnt),x)
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
local r = random(cnt)
if (r>x) then x = r end
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">math.max: 0.437 (156%)</font><br>
<font color="green" style="font-weight:bold">'if > then': 0.282 (100%)</font>
</div>
}}}
Conclusion:
{{{
-> Don't use math.[max|min]() in time critical code!
}}}

== TEST 5: nil checks ('if' vs. 'or') ==
Code1:
{{{
#!lua
for i=1,1000000 do
local y,x
if (random()>0.5) then y=1 end
if (y==nil) then x=1 else x=y end
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
local y
if (random()>0.5) then y=1 end
local x=y or 1
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">nil-check: 0.297 (106%)</font><br>
<font color="green" style="font-weight:bold">a=x or y: 0.281 (100%)</font>
</div>
}}}
Conclusion:
{{{
-> WOW! the or-operator is faster than a nil-check. Use it! :D
}}}

== TEST 6: 'x^2^' vs. 'x*x' ==
Code1:
{{{
#!lua
for i=1,1000000 do
local y = x^2
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
local y = x*x
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">x^2: 1.422 (110%)</font><br>
<font color="green" style="font-weight:bold">x*x: 1.297 (100%)</font>
</div>
}}}

== TEST 7: modulus operators (math.mod vs. %) ==
Code1:
{{{
#!lua
local fmod = math.fmod
for i=1,1000000 do
if (fmod(i,30)<1) then
local x = 1
end
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
if ((i%30)<1) then
local x = 1
end
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">math.mod: 0.281 (355%)</font><br>
<font color="green" style="font-weight:bold">%: 0.079 (100%)</font>
</div>
}}}
Conclusion:
{{{
-> Don't use math.fmod() for positive numbers (for negative ones % and fmod() have different results!)!
}}}

== TEST 8: functions as param for other functions ==
Code1:
{{{
#!lua
local func1 = function(a,b,func)
return func(a+b)
end

for i=1,1000000 do
local x = func1(1,2,function(a) return a*2 end)
end
}}}
Code2:
{{{
#!lua
local func1 = function(a,b,func)
return func(a+b)
end
local func2 = function(a)
return a*2
end

for i=1,1000000 do
local x = func1(1,2,func2)
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">defined in function param: 3.890 (1144%)</font><br>
<font color="green" style="font-weight:bold">defined as local: 0.344 (100%)</font>
</div>
}}}
Conclusion:
{{{
-> REALLY, LOCALIZE YOUR FUNCTIONS ALWAYS BEFORE SENDING THEM INTO ANOTHER FUNCTION!!!
i.e if you use gl.BeginEnd(), gl.CreateList(), ...!!!
}}}

== TEST 9: for-loops ==
Code1:
{{{
#!lua
for i=1,1000000 do
for j,v in pairs(a) do
x=v
end
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
for j,v in ipairs(a) do
x=v
end
end
}}}
Code3:
{{{
#!lua
for i=1,1000000 do
for i=1,100 do
x=a[i]
end
end
}}}
Code4:
{{{
#!lua
for i=1,1000000 do
for i=1,#a do
x=a[i]
end
end
}}}
Code5:
{{{
#!lua
for i=1,1000000 do
local length = #a
for i=1,length do
x=a[i]
end
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
pairs: 3.078 (217%)<br>
<font color="red" style="font-weight:bold">ipairs: 3.344 (236%)</font><br>
<font color="green" style="font-weight:bold">for i=1,x do: 1.422 (100%)</font><br>
for i=1,#atable do 1.422 (100%)<br>
for i=1,atable_length do: 1.562 (110%)
</div>
}}}
Conclusion:
{{{
-> Don't use pairs() or ipairs()!
Try to save the table-size somewhere and use "for i=1,x do"!
}}}

== TEST 10: array access (with [ ]) vs. object access (with .method) ==
Code1:
{{{
#!lua
for i=1,1000000 do
x = a["foo"]
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
x = a.foo
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
atable["foo"]: 1.125 (100%)<br>
atable.foo: 1.141 (101%)
</div>
}}}

== TEST 11: buffered table item access ==
Code1:
{{{
#!lua
for i=1,1000000 do
for n=1,100 do
a[n].x=a[n].x+1
end
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
for n=1,100 do
local y = a[n]
y.x=y.x+1
end
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">'a[n].x=a[n].x+1': 1.453 (127%)</font><br>
<font color="green" style="font-weight:bold">'local y=a[n]; y.x=y.x+1': 1.140 (100%)</font>
</div>
}}}

== TEST 12: adding table items (table.insert vs. [ ]) ==
Code1:
{{{
#!lua
local tinsert = table.insert
for i=1,1000000 do
tinsert(a,i)
end
}}}
Code2:
{{{
#!lua
for i=1,1000000 do
a[i]=i
end
}}}
Code3:
{{{
#!lua
for i=1,1000000 do
a[#a+1]=i
end
}}}
Code4:
{{{
#!lua
local count = 1
for i=1,1000000 do
d[count]=i
count=count+1
end
}}}
Results:
{{{
#!html
<div style="margin-left:25px">
<font color="red" style="font-weight:bold">table.insert: 1.250 (727%)</font><br>
<font color="green" style="font-weight:bold">a[i]: 0.172 (100%)</font><br>
a[#a+1]=x: 0.453 (263%)<br>
a[count++]=x: 0.203 (118%)
</div>
}}}
Conclusion:
{{{
-> Don't use table.insert!!!
Try to save the table-size somewhere and use "a[count+1]=x"!
}}}