w_jn.c

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/* @(#)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"

#ifdef __STDC__
    double jn(int n, double x)  /* wrapper jn */
#else
    double jn(n,x)          /* wrapper jn */
    double x; int n;
#endif
{
#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
}

#ifdef __STDC__
    double yn(int n, double x)  /* wrapper yn */
#else
    double yn(n,x)          /* wrapper yn */
    double x; int n;
#endif
{
#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
}