Android Question Would this improve performance?

[wonder]

Let's say you have a lot of For/Next cycles going on and you desperately need to improve your computing speed. What would you do?

I came up with this idea, reducing all the cycles into a single one.
Would this be a good technique?

Before:

Sub Whatever(Value as int)
    ...
    'Do Stuff
    ...
End Sub

Sub Example
    Dim array_x(512)
    Dim array_y(1024)
    Dim array_z(256)

    Populate_Array(x)
    Populate_Array(y)
    Populate_Array(z)

    For i = 0 to (array_x.Lenght - 1)
        Whatever(array_x(i))
    Next

    For i = 0 to (array_y.Lenght - 1)
        Whatever(array_y(i))
    Next

    For i = 0 to (array_z.Lenght - 1)
        Whatever(array_z(i))
    Next
End Sub

After:

Sub Whatever(Value as int)
    ...
    'Do Stuff
    ...
End Sub

Sub Example
    Dim array_x(512)
    Dim array_y(1024)
    Dim array_z(256)

    Populate_Array(x)
    Populate_Array(y)
    Populate_Array(z)

    For i = 0 to (Max(array_x.Lenght, Max(array_y.Lenght, array_z.Lenght)) - 1)
        Select True
            Case i < array_x.Lenght
                whatever(array_x(i))

            Case i < array_y.Lenght
                whatever(array_y(i))

            Case i < array_z.Lenght
                whatever(array_z(i))
        End Select
    Next
End Sub

 

[sorex]

it all depends what you are trying to do.

why are the sizes different? make them equal and you can leave out the checks that slow down things.
keep a counter that you don't need to go to the end if there are only 10 elements
use a list/map which is counter based already
...

 

[wonder]

it all depends what you are trying to do.

why are the sizes different? make them equal and you can leave out the checks that slow down things.
keep a counter that you don't need to go to the end if there are only 10 elements
use a list/map which is counter based already
...

This is a theoretical situation where there is no guarantee that the arrays will be the same size.
For example processing items which were read from a user generated database. Another example could be a physics engine, 256 galaxies, 512 suns, 1024 planets, all interacting through gravity.

I just want to find the most efficient way to optimize / write scalable code.
Thanks to you, we have already found that the SELECT method is way slower than an IF statement.
Pretty awesome piece of knowledge! I'll never use a SELECT in a cycle again.

 

[wonder]

Regarding C#, it seems that the Switch/Case is faster than the If/Then/Else...
http://www.blackwasp.co.uk/SpeedTestIfElseSwitch.aspx

 

[sorex]

right, but you can't compare one case to another. I don't know how it ends up as java tokenized code and how it gets treatened by the interpreter.

if you look at PC 80x86 assembler an xor of a register with itself (for example xor al,al) is faster than using a plain zero fill mov al,0. Who would've thought that?

optimizing needs to be looked at case specific.