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