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CrySystem/RandGen.cpp

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+#include "StdAfx.h"
+#include "randgen.h"
+
+#define M              (397)                 // a period parameter
+#define K              (0x9908B0DFU)         // a magic constant
+#define hiBit(u)       ((u) & 0x80000000U)   // mask all but highest   bit of u
+#define loBit(u)       ((u) & 0x00000001U)   // mask all but lowest    bit of u
+#define loBits(u)      ((u) & 0x7FFFFFFFU)   // mask     the highest   bit of u
+#define mixBits(u, v)  (hiBit(u)|loBits(v))  // move hi bit of u to hi bit of v
+
+CSysPseudoRandGen::CSysPseudoRandGen()
+{
+	left=-1;
+}
+
+CSysPseudoRandGen::~CSysPseudoRandGen()
+{
+}
+
+void CSysPseudoRandGen::Seed(uint32 seed)
+{
+  //
+  // We initialize state[0..(N-1)] via the generator
+  //
+  //   x_new = (69069 * x_old) mod 2^32
+  //
+  // from Line 15 of Table 1, p. 106, Sec. 3.3.4 of Knuth's
+  // _The Art of Computer Programming_, Volume 2, 3rd ed.
+  //
+  // Notes (SJC): I do not know what the initial state requirements
+  // of the Mersenne Twister are, but it seems this seeding generator
+  // could be better.  It achieves the maximum period for its modulus
+  // (2^30) iff x_initial is odd (p. 20-21, Sec. 3.2.1.2, Knuth); if
+  // x_initial can be even, you have sequences like 0, 0, 0, ...;
+  // 2^31, 2^31, 2^31, ...; 2^30, 2^30, 2^30, ...; 2^29, 2^29 + 2^31,
+  // 2^29, 2^29 + 2^31, ..., etc. so I force seed to be odd below.
+  //
+  // Even if x_initial is odd, if x_initial is 1 mod 4 then
+  //
+  //   the          lowest bit of x is always 1,
+  //   the  next-to-lowest bit of x is always 0,
+  //   the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
+  //   the 3rd-from-lowest bit of x 4-cycles        ... 0 1 1 0 0 1 1 0 ... ,
+  //   the 4th-from-lowest bit of x has the 8-cycle ... 0 0 0 1 1 1 1 0 ... ,
+  //    ...
+  //
+  // and if x_initial is 3 mod 4 then
+  //
+  //   the          lowest bit of x is always 1,
+  //   the  next-to-lowest bit of x is always 1,
+  //   the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
+  //   the 3rd-from-lowest bit of x 4-cycles        ... 0 0 1 1 0 0 1 1 ... ,
+  //   the 4th-from-lowest bit of x has the 8-cycle ... 0 0 1 1 1 1 0 0 ... ,
+  //    ...
+  //
+  // The generator's potency (min. s>=0 with (69069-1)^s = 0 mod 2^32) is
+  // 16, which seems to be alright by p. 25, Sec. 3.2.1.3 of Knuth.  It
+  // also does well in the dimension 2..5 spectral tests, but it could be
+  // better in dimension 6 (Line 15, Table 1, p. 106, Sec. 3.3.4, Knuth).
+  //
+  // Note that the random number user does not see the values generated
+  // here directly since reloadMT() will always munge them first, so maybe
+  // none of all of this matters.  In fact, the seed values made here could
+  // even be extra-special desirable if the Mersenne Twister theory says
+  // so-- that's why the only change I made is to restrict to odd seeds.
+  //
+
+  register uint32 x = (seed | 1U) & 0xFFFFFFFFU, *s = state;
+  register int    j;
+  for(left=0, *s++=x, j=N_RAND_STATE; --j;
+      *s++ = (x*=69069U) & 0xFFFFFFFFU);
+}
+
+uint32 CSysPseudoRandGen::Rand()
+{
+  uint32 y;
+
+  if(--left < 0)
+      return(Reload());
+
+  y  = *next++;
+  y ^= (y >> 11);
+  y ^= (y <<  7) & 0x9D2C5680U;
+  y ^= (y << 15) & 0xEFC60000U;
+  return(y ^ (y >> 18));
+}
+
+float CSysPseudoRandGen::Rand(float fMin, float fMax)
+{
+	static double _1overFFFFFFFF=2.3283064370807973754314699618685e-10;
+	float fVal=(float)((double)Rand()*_1overFFFFFFFF*(double)(fMax-fMin)+(double)fMin);
+	return fVal;
+}
+
+uint32 CSysPseudoRandGen::Reload()
+{
+	register uint32 *p0=state, *p2=state+2, *pM=state+M, s0, s1;
+	register int    j;
+
+	if(left < -1)
+			Seed(4357U);
+
+	left=N_RAND_STATE-1, next=state+1;
+
+	for(s0=state[0], s1=state[1], j=N_RAND_STATE-M+1; --j; s0=s1, s1=*p2++)
+			*p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
+
+	for(pM=state, j=M; --j; s0=s1, s1=*p2++)
+			*p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
+
+	s1=state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
+	s1 ^= (s1 >> 11);
+	s1 ^= (s1 <<  7) & 0x9D2C5680U;
+	s1 ^= (s1 << 15) & 0xEFC60000U;
+	return(s1 ^ (s1 >> 18));
+}