我正在使用蒙特卡罗模拟,我需要用C语言理解这个功能。我希望有人知道如何解释这种做法。谢谢。 //函数即gen随机数
#include <stdlib.h>
#define MBIG 1000000000
#define MSEED 161803398
#define MZ 0
#define FAC (1.0/MBIG)
double ran3(long *idum)
{
static int inext,inextp;
static long ma[56];
static int iff=0;
long mj,mk;
int i,ii,k;
if (*idum < 0 || iff == 0){
iff=1;
mj = labs(MSEED-labs(*idum));
mj %= MBIG;
ma[55]=mj;
mk=1;
for (i=1;i<=54;i++){
ii=(21*i) % 55;
ma[ii]=mk;
mk=mj-mk;
if (mk < MZ) mk += MBIG;
mj =ma[ii];
}
for (k=1;k<=4;k++)
for (i=1;i<=55;i++) {
ma[i] -= ma[1+(i+30) % 55];
if (ma[i] < MZ) ma[i] += MBIG;
}
inext=0;
inext=31;
*idum=1;
}
if (++inext == 56) inext=1;
if (++inextp == 56) inextp=1;
mj =ma[inext]-ma[inextp];
if (mj < MZ) mj += MBIG;
ma[inext] =mj;
return mj*FAC;
}