# source:trunk/sys/libm/w_jn.c@233

Last change on this file since 233 was 1, checked in by alain, 6 years ago

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1
2/* @(#)w_jn.c 5.1 93/09/24 */
3/*
4 * ====================================================
6 *
7 * Developed at SunPro, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14/*
15 * wrapper jn(int n, double x), yn(int n, double x)
16 * floating point Bessel's function of the 1st and 2nd kind
17 * of order n
18 *
19 * Special cases:
20 *      y0(0)=y1(0)=yn(n,0) = -inf with division by zero signal;
21 *      y0(-ve)=y1(-ve)=yn(n,-ve) are NaN with invalid signal.
22 * Note 2. About jn(n,x), yn(n,x)
23 *      For n=0, j0(x) is called,
24 *      for n=1, j1(x) is called,
25 *      for n<x, forward recursion us used starting
26 *      from values of j0(x) and j1(x).
27 *      for n>x, a continued fraction approximation to
28 *      j(n,x)/j(n-1,x) is evaluated and then backward
29 *      recursion is used starting from a supposed value
30 *      for j(n,x). The resulting value of j(0,x) is
31 *      compared with the actual value to correct the
32 *      supposed value of j(n,x).
33 *
34 *      yn(n,x) is similar in all respects, except
35 *      that forward recursion is used for all
36 *      values of n>1.
37 *
38 */
39
40#include <libm/fdlibm.h>
41
42#ifdef __STDC__
43        double jn(int n, double x)      /* wrapper jn */
44#else
45        double jn(n,x)                  /* wrapper jn */
46        double x; int n;
47#endif
48{
49#ifdef _IEEE_LIBM
50        return __ieee754_jn(n,x);
51#else
52        double z;
53        z = __ieee754_jn(n,x);
54        if(_LIB_VERSION == _IEEE_ || isnan(x) ) return z;
55        if(fabs(x)>X_TLOSS) {
56            return __kernel_standard((double)n,x,38); /* jn(|x|>X_TLOSS,n) */
57        } else
58            return z;
59#endif
60}
61
62#ifdef __STDC__
63        double yn(int n, double x)      /* wrapper yn */
64#else
65        double yn(n,x)                  /* wrapper yn */
66        double x; int n;
67#endif
68{
69#ifdef _IEEE_LIBM
70        return __ieee754_yn(n,x);
71#else
72        double z;
73        z = __ieee754_yn(n,x);
74        if(_LIB_VERSION == _IEEE_ || isnan(x) ) return z;
75        if(x <= 0.0){
76                if(x==0.0)
77                    /* d= -one/(x-x); */
78                    return __kernel_standard((double)n,x,12);
79                else
80                    /* d = zero/(x-x); */
81                    return __kernel_standard((double)n,x,13);
82        }
83        if(x>X_TLOSS) {
84            return __kernel_standard((double)n,x,39); /* yn(x>X_TLOSS,n) */
85        } else
86            return z;
87#endif
88}
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