w_jn.c

/* @(#)w_jn.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/*
 * wrapper jn(int n, double x), yn(int n, double x)
 * floating point Bessel's function of the 1st and 2nd kind
 * of order n
 *          
 * Special cases:
 *      y0(0)=y1(0)=yn(n,0) = -inf with division by zero signal;
 *      y0(-ve)=y1(-ve)=yn(n,-ve) are NaN with invalid signal.
 * Note 2. About jn(n,x), yn(n,x)
 *      For n=0, j0(x) is called,
 *      for n=1, j1(x) is called,
 *      for n<x, forward recursion us used starting
 *      from values of j0(x) and j1(x).
 *      for n>x, a continued fraction approximation to
 *      j(n,x)/j(n-1,x) is evaluated and then backward
 *      recursion is used starting from a supposed value
 *      for j(n,x). The resulting value of j(0,x) is
 *      compared with the actual value to correct the
 *      supposed value of j(n,x).
 *
 *      yn(n,x) is similar in all respects, except
 *      that forward recursion is used for all
 *      values of n>1.
 *      
 */

#include "fdlibm.h"

 double jn(int n, double x)      /* wrapper jn */
{
#ifdef _IEEE_LIBM
        return __ieee754_jn(n,x);
#else
        double z;
        z = __ieee754_jn(n,x);
        if(_LIB_VERSION == _IEEE_ || isnan(x) ) return z;
        if(fabs(x)>X_TLOSS) {
            return __kernel_standard((double)n,x,38); /* jn(|x|>X_TLOSS,n) */
        } else
            return z;
#endif
}

double yn(int n, double x)      /* wrapper yn */
{
#ifdef _IEEE_LIBM
        return __ieee754_yn(n,x);
#else
        double z;
        z = __ieee754_yn(n,x);
        if(_LIB_VERSION == _IEEE_ || isnan(x) ) return z;
        if(x <= 0.0){
                if(x==0.0)
                    /* d= -one/(x-x); */
                    return __kernel_standard((double)n,x,12);
                else
                    /* d = zero/(x-x); */
                    return __kernel_standard((double)n,x,13);
        }
        if(x>X_TLOSS) {
            return __kernel_standard((double)n,x,39); /* yn(x>X_TLOSS,n) */
        } else
            return z;
#endif
}