z_sqrt.c   [plain text]

#include "f2c.h"

#undef abs
#include "math.h"
extern double f__cabs (double, double);
void
z_sqrt (doublecomplex * r, doublecomplex * z)
{
  double mag, zi = z->i, zr = z->r;

  if ((mag = f__cabs (zr, zi)) == 0.)
    r->r = r->i = 0.;
  else if (zr > 0)
    {
      r->r = sqrt (0.5 * (mag + zr));
      r->i = zi / r->r / 2;
    }
  else
    {
      r->i = sqrt (0.5 * (mag - zr));
      if (zi < 0)
	r->i = -r->i;
      r->r = zi / r->i / 2;
    }
}