Opposite Power in wc3?

[shadowvzs]

sorry for too stupid quetsion but i dont got how can i get the opposite of power

so let say Pow(2,3)=8
how could i convert back 8 to 3?

only way the making a loop and compare each time x=x*2 with 8 and count the loop?

 

[LeP]

You are probably looking for the logarithm of a number.
log2(8) means the number which 2 has to be raised by to get 8, aka. 3 because 2³=8.
Here is a general script for logarithms.

e: Also this.
e: But if you only want the logarithms of base 2 and only integer results there are faster ways doing that.

 

[Dr Super Good]

You use log to the base 2. They teach you this in mathematics.

Ofcourse you can get log to any base from any other base.
log2(x) = ln(x)/ln(2)

Sadly WC3 has no native support for logs. You will have to derive the logs though very slow opperations which might have to sacrifice precision for speed.

 

[shadowvzs]

so dont have a simple command way

i know how to make it with loop but i hoped have a shorter form.

i also want skip in loop the pow since i heard pow(x,x) is slower than x*x

function log takes integer n returns integer
local integer i = 2
local integer c = 1
if n == 1 then
set c = 0
endif
loop
exitwhen i >= n
set c = c + 1
set i = i * 2
endloop
return c
endfunction

 

[Dr Super Good]

That log has incorrect behaviour...

 

[shadowvzs]

That log has incorrect behaviour...

ok but acctually i must use only for condition and it allways 2 ^ x, and not a normal log, so why wrong?

 

[Dr Super Good]

Firstly it deals with integers, logs can be fractional.
Secondly it returns an incorrect value for a log of a negative or 0 (some error should happen here).

The way you currently have it you would be better off using a look up table and incriment through it instead of computing each value each time.

 

[shadowvzs]

Firstly it deals with integers, logs can be fractional.
Secondly it returns an incorrect value for a log of a negative or 0 (some error should happen here).

The way you currently have it you would be better off using a look up table and incriment through it instead of computing each value each time.

but i dont use engative numbers just 2^0-29

u mean save to hashtable or what table u mean?

ok its faster than last example no?

map init

    loop
        exitwhen i > udg_Buff_Max
        set udg_Buff_ID2V[i] = R2I(Pow(2,i))
        set i = i + 1
    endloop

header func

function log takes integer n returns integer
    local integer i = 2
    if n == 1 then
    endif
    loop
        exitwhen udg_Buff_ID2V[i] == n
        set i = i + 1
    endloop
    return i
endfunction

 

[Dr Super Good]

exitwhen udg_Buff_ID2V == n.
This will mean it will only work for values that are exactly powers of 2. Any other value will cause a thread crash due to hitting the oplimit.

 

[shadowvzs]

but in my case every number is power of 2. i think its fastest potentional way

 

[von_Oberstain]

sorry for too stupid quetsion but i dont got how can i get the opposite of power

so let say Pow(2,3)=8
how could i convert back 8 to 3?

only way the making a loop and compare each time x=x*2 with 8 and count the loop?

Pow(8,0.333)

EDIT: whoops, you're looking for 3, not 2, sry

 

[Bribe]

Here is a logarithm tool uploaded in our JASS section - http://www.hiveworkshop.com/forums/jass-resources-412/snippet-natural-logarithm-108059/

Thanks for your inquiry. Until today I never knew the purpose of the logarithm function. But I should have known the whole time, my school was not very good with math courses.

 

[WaterKnight]

Of course TC has a point. There is no need to use the general approach when his/her case is limited and can be optimized.

 

[Bribe]

Yeah, like Dr SuperGood alluded to and to quote what Dark_Dragon posted, this way is the most optimized for integers (possibly a non-recursion option would be faster):

// *** Returns log from given values ***
constant function log takes integer base, integer result returns integer
    if (result == 1) then
        return 0
    endif
    return log(base, result/base)+1
endfunction