#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void uv2ddff(double u,double v,size_t *dd,double *ff)
{
/* pass in the u- and v-components and locations for the wind direction and
   speed, which are calculated by uv2ddff */

  const double pi=3.141592654,deg=180./pi;
  double hypot,div;

  hypot=sqrt(u*u+v*v);
  *ff=hypot+0.5;
  if (*ff < 0.00001)
    *dd=0;
  else {
    div=fabs(v)/hypot;
    if (div > 1.) {
	if (div < 1.00001)
	  div=1.;
	else {
	  fprintf(stderr,"Error in uv2ddff: bad quotient for acos()\n");
	  exit(1);
	}
    }
    *dd=acos(div)*deg+0.5;
    if (u >= 0)
	*dd= (v >= 0) ? *dd+180 : 360-*dd;
    else if (u <= 0 && v >= 0)
	*dd=180-*dd;
  }
}

void ddff2uv(size_t dd,double ff,double *u,double *v)
{
/* pass in the wind direction and wind speed and locations for the u- and v-
   wind components, which are calculated by ddff2uv */

  const double pi=3.141592654,rad=pi/180.;
  double ang;

  ang=((double)dd+90.)*rad;
  *u=ff*cos(ang);
  *v=-ff*sin(ang);
}