C++生成随机数：负二项分布/帕斯卡分布（negative binomial distribution）

long cls_random::randomNegativeBinomial(
double    r,
double  probability)
{
long rnd = 0;
double fr = 0.0;
while(true)
{
double pV = (double)rand()/(double)RAND_MAX;
if (pV<probability)
{
rnd++;
}
else
{
fr++;
}
if (fr>r)
{
break;
}
}
return rnd;
}