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#include "f2c.h"
#ifdef KR_headers
double log(), f__cabs(), atan2();
VOID z_log(r, z) doublecomplex *r, *z;
#else
#undef abs
#include "math.h"
extern double f__cabs(double, double);
void z_log(doublecomplex *r, doublecomplex *z)
#endif
{
double s, s0, t, t2, u, v;
double zi = z->i, zr = z->r;
r->i = atan2(zi, zr);
#ifdef Pre20000310
r->r = log( f__cabs( zr, zi ) );
#else
if (zi < 0)
zi = -zi;
if (zr < 0)
zr = -zr;
if (zr < zi) {
t = zi;
zi = zr;
zr = t;
}
t = zi/zr;
s = zr * sqrt(1 + t*t);
/* now s = f__cabs(zi,zr), and zr = |zr| >= |zi| = zi */
if ((t = s - 1) < 0)
t = -t;
if (t > .01)
r->r = log(s);
else {
#ifdef Comment
log(1+x) = x - x^2/2 + x^3/3 - x^4/4 + - ...
= x(1 - x/2 + x^2/3 -+...)
[sqrt(y^2 + z^2) - 1] * [sqrt(y^2 + z^2) + 1] = y^2 + z^2 - 1, so
sqrt(y^2 + z^2) - 1 = (y^2 + z^2 - 1) / [sqrt(y^2 + z^2) + 1]
#endif /*Comment*/
t = ((zr*zr - 1.) + zi*zi) / (s + 1);
t2 = t*t;
s = 1. - 0.5*t;
u = v = 1;
do {
s0 = s;
u *= t2;
v += 2;
s += u/v - t*u/(v+1);
} while(s > s0);
r->r = s*t;
}
#endif
}
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