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      1 /* @(#)w_jn.c 5.1 93/09/24 */
      2 /*
      3  * ====================================================
      4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      5  *
      6  * Developed at SunPro, a Sun Microsystems, Inc. business.
      7  * Permission to use, copy, modify, and distribute this
      8  * software is freely granted, provided that this notice
      9  * is preserved.
     10  * ====================================================
     11  */
     12 
     13 #include <sys/cdefs.h>
     14 #if defined(LIBM_SCCS) && !defined(lint)
     15 __RCSID("$NetBSD: w_jn.c,v 1.9 2002/05/26 22:02:01 wiz Exp $");
     16 #endif
     17 
     18 /*
     19  * wrapper jn(int n, double x), yn(int n, double x)
     20  * floating point Bessel's function of the 1st and 2nd kind
     21  * of order n
     22  *
     23  * Special cases:
     24  *	y0(0)=y1(0)=yn(n,0) = -inf with division by zero signal;
     25  *	y0(-ve)=y1(-ve)=yn(n,-ve) are NaN with invalid signal.
     26  * Note 2. About jn(n,x), yn(n,x)
     27  *	For n=0, j0(x) is called,
     28  *	for n=1, j1(x) is called,
     29  *	for n<x, forward recursion us used starting
     30  *	from values of j0(x) and j1(x).
     31  *	for n>x, a continued fraction approximation to
     32  *	j(n,x)/j(n-1,x) is evaluated and then backward
     33  *	recursion is used starting from a supposed value
     34  *	for j(n,x). The resulting value of j(0,x) is
     35  *	compared with the actual value to correct the
     36  *	supposed value of j(n,x).
     37  *
     38  *	yn(n,x) is similar in all respects, except
     39  *	that forward recursion is used for all
     40  *	values of n>1.
     41  *
     42  */
     43 
     44 #include "math.h"
     45 #include "math_private.h"
     46 
     47 double
     48 jn(int n, double x)	/* wrapper jn */
     49 {
     50 #ifdef _IEEE_LIBM
     51 	return __ieee754_jn(n,x);
     52 #else
     53 	double z;
     54 	z = __ieee754_jn(n,x);
     55 	if(_LIB_VERSION == _IEEE_ || isnan(x) ) return z;
     56 	if(fabs(x)>X_TLOSS) {
     57 	    return __kernel_standard((double)n,x,38); /* jn(|x|>X_TLOSS,n) */
     58 	} else
     59 	    return z;
     60 #endif
     61 }
     62 
     63 double
     64 yn(int n, double x)	/* wrapper yn */
     65 {
     66 #ifdef _IEEE_LIBM
     67 	return __ieee754_yn(n,x);
     68 #else
     69 	double z;
     70 	z = __ieee754_yn(n,x);
     71 	if(_LIB_VERSION == _IEEE_ || isnan(x) ) return z;
     72         if(x <= 0.0){
     73                 if(x==0.0)
     74                     /* d= -one/(x-x); */
     75                     return __kernel_standard((double)n,x,12);
     76                 else
     77                     /* d = zero/(x-x); */
     78                     return __kernel_standard((double)n,x,13);
     79         }
     80 	if(x>X_TLOSS) {
     81 	    return __kernel_standard((double)n,x,39); /* yn(x>X_TLOSS,n) */
     82 	} else
     83 	    return z;
     84 #endif
     85 }
     86