ran0.c

来自「IBM(原)数据生成器和源代码」· C语言 代码 · 共 27 行

#define IA 16807
#define IM 2147483647
#define AM (1.0/IM)
#define IQ 127773
#define IR 2836
#define MASK 123459876

float ran0(long &idum)
// "Minimal" random number generator of Park and Miller with
// Bays-Durham shuffle and added safeguards. Returns a uniform random
// deviate between 0.0 and 1.0. Set or reset idum to any integer value
// (except the unlikely value MASK) to initialize the sequence; idum
// must not be altered between calls for successive deviates in a sequence. 
{
  long k;
  float ans;
  
  idum ^= MASK;			  // XORing with MASK allows use of 0 and
  k = idum/IQ;			  //     other simple bit patterns for idum.
  idum = IA * (idum-k*IQ) - IR*k; // Compute idum = (IA*idum) % IM without
  if (idum < 0) idum += IM;	  //     overflows by Schrage's method.
  ans = AM * idum;		  // Convert idum to a floating result.
  idum ^= MASK;			  // Unmask before return.
  return ans;
}