c_sqrt.c

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#include "v3p_f2c.h"

#ifdef KR_headers
extern double sqrt(), f__cabs();

VOID c_sqrt(r, z) complex *r, *z;
#else
#undef abs
#include "math.h"
#ifdef __cplusplus
extern "C" {
#endif
extern double f__cabs(double, double);

#undef complex
#define complex v3p_netlib_complex

void c_sqrt(complex *r, complex *z)
#endif
{
        double mag, t;
        double zi = z->i, zr = z->r;

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