[Wesnoth-wiki-changes] PseudoRandomNumberGeneration

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Index: PseudoRandomNumberGeneration
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RCS file: /home/wesnoth/cvsroot/wikiroot/PseudoRandomNumberGeneration,v
retrieving revision 1.10
diff -u -r1.10 PseudoRandomNumberGeneration
--- PseudoRandomNumberGeneration        14 Nov 2004 16:22:13 -0000      1.10
+++ PseudoRandomNumberGeneration        15 Nov 2004 02:06:37 -0000
@@ -1,7 +1,9 @@
- Elvish Pillager: I have finished my work on the Pseudorandom Number 
Generation! It's done! I found a lot of bugs on the way...
+ Elvish Pillager: I have finished my work on the Pseudorandom Number 
Generation! It's done! I found a lot of bugs on the
+way...
  I think I'll wait until the site is back up to go in depth.
 
- Also, I noticed that a Grand Knight with Holy Water led by a Grand Marshal 
during the day can kill a Skeletal Dragon in one hit, something that Túrin
+ Also, I noticed that a Grand Knight with Holy Water led by a Grand Marshal 
during the day can kill a Skeletal Dragon in
+one hit, something that Túrin
  might want to do something about. (It's easy to slaughter the Skeletal Dragon 
without being attacked by the other undead.)
 .
  Shadowfury333: What exactly is this for?
@@ -135,28 +137,45 @@
 
  I got my pseudorandom number generation (to be referred to as PRNG) formula 
from a book by Knuth. It is as follows:
  Xn+1=(aXn + c) mod m
- That was difficult to do in code. I don't have multiplication[1] OR modulus 
in my arsenal, so I had to imitate them using while loops.
- Then, I had to choose good values for a, c, and m. Since the 'random' 
sequence always loops eventually, the duration of the loop is called the period.
+ That was difficult to do in code. I don't have multiplication[1] OR modulus 
in my arsenal, so I had to imitate them
+using while loops.
+ Then, I had to choose good values for a, c, and m. Since the 'random' 
sequence always loops eventually, the duration of
+the loop is called the period.
  In order to have a period of length m, the maximum, the numbers had to fill 
several conditions.
- That wasn't hard, but the numbers were at first way too small. I increased 
them. They did not fulfill my worries that the the process would be too slow,
- fortunately, though it's much MUCH slower than doing these operations in a 
standalone C application or whatever. Something like that could go
+ That wasn't hard, but the numbers were at first way too small. I increased 
them. They did not fulfill my worries that
+the the process would be too slow,
+ fortunately, though it's much MUCH slower than doing these operations in a 
standalone C application or whatever.
+Something like that could go
  through all 32768 possible values in less than a second.
- Anyway, I at first made the mistake of extracting values by regenerating the 
randomseed until it was below the requested value. (that was incredibly
- stupid. It means that there are only so many possible values, thus it wrecks 
the randomseed.) After that I used modulus extraction, which is still not
+ Anyway, I at first made the mistake of extracting values by regenerating the 
randomseed until it was below the
+requested value. (that was incredibly
+ stupid. It means that there are only so many possible values, thus it wrecks 
the randomseed.) After that I used modulus
+extraction, which is still not
  the best, but at least it works.
- At one point, I ran across a strange problem: Generating pairs of values, I 
kept getting the same pairs! There was something wrong with my PRNG. It
- turns out that each number easily predicts the next number, until it hits the 
modulus. Therefore, I increased a and c so that it hit the modulus almost
+ At one point, I ran across a strange problem: Generating pairs of values, I 
kept getting the same pairs! There was
+something wrong with my PRNG. It
+ turns out that each number easily predicts the next number, until it hits the 
modulus. Therefore, I increased a and c
+so that it hit the modulus almost
  every time, while still conforming to the required conditions.
- Another problem was more frustrating but easier to solve once I found it: The 
values kept incrementing steadily instead of being random! I spent a
- long time puzzling over this before I realized that changing the multiplier 
wasn't having any effect. I investigated, and found a missing $.
- The last problem I encountered was a bug in Wesnoth. That bug is that 
variables remain in existence and retain their values between multiplayer
+ Another problem was more frustrating but easier to solve once I found it: The 
values kept incrementing steadily instead
+of being random! I spent a
+ long time puzzling over this before I realized that changing the multiplier 
wasn't having any effect. I investigated,
+and found a missing $.
+ The last problem I encountered was a bug in Wesnoth. That bug is that 
variables remain in existence and retain their
+values between multiplayer
  games. I circumvented this by clearing all my variables at the start of the 
game.
 
- Throughout most of this, I had a bugtester on the multiplayer server called 
Jammet. I thank you, Jammet, for your patience while I fixed
+ Throughout most of this, I had a bugtester on the multiplayer server called 
Jammet. I thank you, Jammet, for your
+patience while I fixed
  incomprehensible bug after incomprehensible bug. Your help was very helpful.
 
- [1] there is also a bug in multiplication; apperently floating-point 
multiplication and subsequently casting floats to ints throws off their values 
on
+ [1] there is also a bug in multiplication; apperently floating-point 
multiplication and subsequently casting floats to
+ints throws off their values on
  some operating systems.
+.
+ Joshbosh321: can you post that multiplayer map that you were using to, I 
assume, playtest this RNG?  I played against
+ you once and found the concept very interesting...
+.
 
 ||See Also||