[Fractdev] Phew! No "conjbug"

30 May 2003

      Jonathan, there's no "conjbug". See my long message in the other 
forum.

In researching this I noticed that the Xfractint function:

void FPUcplxlog_CMPLX *x, _CMPLX *z)
{
    double mod,zx,zy;
    mod = sqrt(x->x*x->x + x->y*x->y);
    zx = log(mod);
    zy = atan2(x->y,x->x);

    z->x = zx;
    z->y = zy;
}

could be speeded up by getting rid of the sqrt() at the cost of a 
multiply:

void FPUcplxlog_CMPLX *x, _CMPLX *z)
{
    double zx,zy;
    zx = .5*log(x->x*x->x + x->y*x->y);
    zy = atan2(x->y,x->x);

    z->x = zx;
    z->y = zy;
}

There's no downside that I can see, the two are mathematically 
equivalent, and the faster version is just as readable. I didn't 
benchmark the different but I'll bet it's measurable.

Tim

[Fractdev] Phew! No "conjbug"

Tim Wegner