Talk:GetRandomPercent

Morrowind's Random100

Is this similar to Morrowind's Random100 function, or can it be used in the same manner? The Imperial Dragon 12:58, 11 June 2006 (EDT)

Random100 (as one word) in Morrowind was a global that was set to 0-100 once per frame (in the script "Main")

set variable to GetRandomPercent 

in Oblivion is the same as

set variable to Random 100

in Morrowind and will return a new random number ranging from 0-99 whenever you call it.

--JOG 13:40, 11 June 2006 (EDT)

I see, thank you. The Imperial Dragon 13:44, 11 June 2006 (EDT)

Example

JOG 17:33, 29 July 2006 (EDT): Here's the math behind the first example:

short dice
set dice to 1 + 0.06 * GetRandompercent  

int(1 + 0.06 * 00) = int(1 + 0.00) = int(1.00) = 1

int(1 + 0.06 * 16) = int(1 + 0.96) = int(1.96) = 1 => Chance: 17%

int(1 + 0.06 * 17) = int(1 + 1.02) = int(2.02) = 2

int(1 + 0.06 * 33) = int(1 + 1.98) = int(2.98) = 2 => Chance: 17%

int(1 + 0.06 * 34) = int(1 + 2.02) = int(3.02) = 3

int(1 + 0.06 * 49) = int(1 + 2.94) = int(3.94) = 3 => Chance: 16%

int(1 + 0.06 * 50) = int(1 + 3.00) = int(4.00) = 4

int(1 + 0.06 * 66) = int(1 + 3.96) = int(4.96) = 4 => Chance: 17%

int(1 + 0.06 * 67) = int(1 + 4.02) = int(5.02) = 5

int(1 + 0.06 * 83) = int(1 + 4.98) = int(5.98) = 5 => Chance: 17%

int(1 + 0.06 * 84) = int(1 + 5.04) = int(6.04) = 6

int(1 + 0.06 * 99) = int(1 + 5.94) = int(6.94) = 6 => Chance: 16%

short dice
set dice to 6.0/99 * GetRandompercent 

Is the loaded variant and returns this:

int(6/99 * 00) = int(0.00) = 0

int(6/99 * 16) = int(0.97) = 0 => Chance: 17%

int(5/99 * 17) = int(1.03) = 1

int(5/99 * 32) = int(1.94) = 1 => Chance: 16%

int(5/99 * 33) = int(2.00) = 2

int(5/99 * 49) = int(2.97) = 2 => Chance: 17%

int(5/99 * 50) = int(3.03) = 3

int(5/99 * 65) = int(3.94) = 3 => Chance: 16%

int(5/99 * 66) = int(4.00) = 4

int(5/99 * 82) = int(4.97) = 4 => Chance: 17%

int(5/99 * 83) = int(5.03) = 5

int(5/99 * 98) = int(5.94) = 5 => Chance: 16%

int(5/99 * 99) = int(6.00) = 6 => Chance: 1%

Alternative up to 50

Seems to me that for Random Numbers up to 50 you can use this Syntax:

short var
Set var to ( GetRandomPercent % <2..50> ) + 1

Where "Percent Sign" is the Modulus Operator...

Should effectively give every value 2 thru 50 an equal chance... Dejunai 13:38, 31 August 2006 (EDT)

Hehe, don't betray all the secrets of the "cryptic" coders :)--JOG 14:02, 31 August 2006 (EDT)

Algorithm

Here's the hex of the function

call    sub_47DDA0; returns system time? calls GetSystemTimeAsFileTime
mov     edi, eax
mov     eax, 0AE147AE1h; or some other constant
imul    edi
sar     edx, 5
mov     eax, edx
shr     eax, 1Fh
add     eax, edx
imul    eax, 64h
add     edi, eax

From Ian Patterson "That function is a wrapper around MS' stdlib rand that calls srand(time(NULL)) if it hasn't been seeded yet. It only uses the system timer once. The rest of the code is just some modular arithmetic done in fixed point."--Haama 13:42, 25 May 2008 (EDT)

Should add that Ian's point was, GetRandomPercent is not especially random. Use rand instead if that is important. Scruggs 23:33, 13 August 2008 (EDT)