lib/libm/src/w_jn.c

   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 }