/* Copyright (C) 2017 - IIT Bombay - FOSSEE

 This file must be used under the terms of the CeCILL.
 This source file is licensed as described in the file COPYING, which
 you should have received as part of this distribution.  The terms
 are also available at
 http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
 Organization: FOSSEE, IIT Bombay
 Author: Brijesh Gupta C R
 Email: toolbox@scilab.in
*/
#include <stdio.h>
#include     "math.h"
#include     "besselk.h"

#define ACC 40.0
#define BIGNO 1.0e10
#define BIGNI 1.0e-10

static float fbessi0( float x )
{
   float ax,ans;
   float y;


   if ((ax=fabs(x)) < 3.75) {
      y=x/3.75,y=y*y;
      ans=1.0+y*(3.5156229+y*(3.0899424+y*(1.2067492
         +y*(0.2659732+y*(0.360768e-1+y*0.45813e-2)))));
   } else {
      y=3.75/ax;
      ans=(exp(ax)/sqrt(ax))*(0.39894228+y*(0.1328592e-1
         +y*(0.225319e-2+y*(-0.157565e-2+y*(0.916281e-2
         +y*(-0.2057706e-1+y*(0.2635537e-1+y*(-0.1647633e-1
         +y*0.392377e-2))))))));
   }
   return ans;
}




static float fbessi1( float x)
{
   float ax,ans;
   float y;


   if ((ax=fabs(x)) < 3.75) {
      y=x/3.75,y=y*y;
      ans=ax*(0.5+y*(0.87890594+y*(0.51498869+y*(0.15084934
         +y*(0.2658733e-1+y*(0.301532e-2+y*0.32411e-3))))));
   } else {
      y=3.75/ax;
      ans=0.2282967e-1+y*(-0.2895312e-1+y*(0.1787654e-1
         -y*0.420059e-2));
      ans=0.39894228+y*(-0.3988024e-1+y*(-0.362018e-2
         +y*(0.163801e-2+y*(-0.1031555e-1+y*ans))));
      ans *= (exp(ax)/sqrt(ax));
   }
   return x < 0.0 ? -ans : ans;
}


static float fbessk0( float x )
{
   float y,ans;

   if (x <= 2.0) {
      y=x*x/4.0;
      ans=(-log(x/2.0)*fbessi0(x))+(-0.57721566+y*(0.42278420
         +y*(0.23069756+y*(0.3488590e-1+y*(0.262698e-2
         +y*(0.10750e-3+y*0.74e-5))))));
   } else {
      y=2.0/x;
      ans=(exp(-x)/sqrt(x))*(1.25331414+y*(-0.7832358e-1
         +y*(0.2189568e-1+y*(-0.1062446e-1+y*(0.587872e-2
         +y*(-0.251540e-2+y*0.53208e-3))))));
   }
   return ans;
}




static float fbessk1( float x )
{
   float y,ans;

   if (x <= 2.0) {
      y=x*x/4.0;
      ans=(log(x/2.0)*fbessi1(x))+(1.0/x)*(1.0+y*(0.15443144
         +y*(-0.67278579+y*(-0.18156897+y*(-0.1919402e-1
         +y*(-0.110404e-2+y*(-0.4686e-4)))))));
   } else {
      y=2.0/x;
      ans=(exp(-x)/sqrt(x))*(1.25331414+y*(0.23498619
         +y*(-0.3655620e-1+y*(0.1504268e-1+y*(-0.780353e-2
         +y*(0.325614e-2+y*(-0.68245e-3)))))));
   }
   return ans;
}

float fbessk( int n, float x )
{
   int j;
   float bk,bkm,bkp,tox;


   if (n < 0 || x == 0.0)
   {
      float   dblank;
      return( dblank );
   }
   if (n == 0)
      return( fbessk0(x) );
   if (n == 1)
      return( fbessk1(x) );

   tox=2.0/x;
   bkm=fbessk0(x);
   bk=fbessk1(x);
   for (j=1;j<n;j++) {
      bkp=bkm+j*tox*bk;
      bkm=bk;
      bk=bkp;
   }
   return bk;
}

void sbesselka(float* inp1,int size1, float* inp2,int size2, float* oup)
{
    int i;
    if(size1 != size2)
        printf("Error! arguments #1 and #2 have incompatible dimensions.");
    for(i = 0; i<size1;i++)
    {
        oup[i] = fbessk(inp1[i],inp2[i]);
    }
}