- Resetting Randomizer with 0 or no longer breaks it (will be set to 1). Same...

- Resetting Randomizer with 0 or no longer breaks it (will be set to 1). Same for other numbers for which it wasn't defined.
- Randomizer now returns range 0..randMax as documented and no longer 1..randMax as it did before. randMax got reduced by 1.
- Using now same random numbers as std::minstd_rand0. Not sure if the others were wrong, but documentation mentioned they are for mixed linear congruential generator from L'Ecuyer and as far as I can see we don't use that (that one mixes 2 calculations). We seem to use just a linear congruential generator. (I'm no expert on all this, just what it looks like from net articles).


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@5243 dfc29bdd-3216-0410-991c-e03cc46cb475

changes.txt

 --------------------------
 Changes in 1.9 (not yet released)
 
+- Randomizer now returns range 0..randMax as documented and no longer 1..randMax as it did before. randMax got reduced by 1.
+- Resetting Randomizer with 0 or no longer breaks it (will be set to 1). Same for other numbers for which it wasn't defined.
 - Add SMaterialLayer::TextureWrapW for cubemap texture wrap mode at W axis.
 - Add cubemap texture support for D3D9 and OpenGL drivers.
 - Do no longer re-calculate md2 frames when they don't change (thx @npc for reporting)

source/Irrlicht/os.cpp

@@ -196,7 +196,7 @@ namespace os
 
 	// our Randomizer is not really os specific, so we
 	// code one for all, which should work on every platform the same,
-	// which is desireable.
+	// which is desirable.
 
 	s32 Randomizer::seed = 0x0f0f0f0f;
 
@@ -205,10 +205,10 @@ namespace os
 	{
 		// (a*seed)%m with Schrage's method
 		seed = a * (seed%q) - r* (seed/q);
-		if (seed<0)
+		if (seed<1)
 			seed += m;
 
-		return seed;
+		return seed-1;	// -1 because we want it to start at 0
 	}
 
 	//! generates a pseudo random number
@@ -225,7 +225,12 @@ namespace os
 	//! resets the randomizer
 	void Randomizer::reset(s32 value)
 	{
-		seed = value;
+		if (value<0)
+			seed = value+m;
+		else if ( value == 0 || value == m)
+			seed = 1;
+		else
+			seed = value;
 	}
 
 

source/Irrlicht/os.h

@@ -43,8 +43,8 @@ namespace os
 	};
 
 
-	// mixed linear congruential generator (MLCG)
-	// numbers chosen according to L'Ecuyer, Commun. ACM 31 (1988) 742
+	// congruential pseudo-random generator
+	// numbers identical to std::minstd_rand0
 	// period is somewhere around m-1
 	class Randomizer
 	{
@@ -59,17 +59,18 @@ namespace os
 		//! generates a pseudo random number in the range 0..1
 		static f32 frand();
 
-		//! get maxmimum number generated by rand()
+		//! get maximum number generated by rand()
 		static s32 randMax();
 
 	private:
 
 		static s32 seed;
-		static const s32 m = 2147483399;	// a non-Mersenne prime
-		static const s32 a = 40692;			// another spectral success story
+
+		static const s32 m = 2147483647;	// a Mersenne prime (2^31-1)
+		static const s32 a = 16807;			// another spectral success story
 		static const s32 q = m/a;
 		static const s32 r = m%a;			// again less than q
-		static const s32 rMax = m-1;
+		static const s32 rMax = m-2;
 	};