Function largest_prime_factor

numpy/fft/_pocketfft.c:217–235

  }

NOINLINE static size_t largest_prime_factor (size_t n)
  {
  size_t res=1;
  size_t tmp;
  while (((tmp=(n>>1))<<1)==n)
    { res=2; n=tmp; }

  size_t limit=(size_t)sqrt(n+0.01);
  for (size_t x=3; x<=limit; x+=2)
  while (((tmp=(n/x))*x)==n)
    {
    res=x;
    n=tmp;
    limit=(size_t)sqrt(n+0.01);
    }
  if (n>1) res=n;

  return res;
  }

NOINLINE static double cost_guess (size_t n)
  {