2 * Copyright (c) 1992, 1993
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * @(#)jn.c 8.2 (Berkeley) 11/30/93
38 * Minor modifications by Peter McIlroy to adapt non-IEEE architecture.
42 * ====================================================
43 * Copyright (C) 1992 by Sun Microsystems, Inc.
45 * Developed at SunPro, a Sun Microsystems, Inc. business.
46 * Permission to use, copy, modify, and distribute this
47 * software is freely granted, provided that this notice
49 * ====================================================
51 * ******************* WARNING ********************
52 * This is an alpha version of SunPro's FDLIBM (Freely
53 * Distributable Math Library) for IEEE double precision
54 * arithmetic. FDLIBM is a basic math library written
55 * in C that runs on machines that conform to IEEE
56 * Standard 754/854. This alpha version is distributed
57 * for testing purpose. Those who use this software
58 * should report any bugs to
60 * fdlibm-comments@sunpro.eng.sun.com
62 * -- K.C. Ng, Oct 12, 1992
63 * ************************************************
67 * jn(int n, double x), yn(int n, double x)
68 * floating point Bessel's function of the 1st and 2nd kind
72 * y0(0)=y1(0)=yn(n,0) = -inf with division by zero signal;
73 * y0(-ve)=y1(-ve)=yn(n,-ve) are NaN with invalid signal.
74 * Note 2. About jn(n,x), yn(n,x)
75 * For n=0, j0(x) is called,
76 * for n=1, j1(x) is called,
77 * for n<x, forward recursion us used starting
78 * from values of j0(x) and j1(x).
79 * for n>x, a continued fraction approximation to
80 * j(n,x)/j(n-1,x) is evaluated and then backward
81 * recursion is used starting from a supposed value
82 * for j(n,x). The resulting value of j(0,x) is
83 * compared with the actual value to correct the
84 * supposed value of j(n,x).
86 * yn(n,x) is similar in all respects, except
87 * that forward recursion is used for all
96 #if defined(vax) || defined(tahoe)
100 #define infnan(x) (0.0)
104 invsqrtpi= 5.641895835477562869480794515607725858441e-0001,
116 /* J(-n,x) = (-1)^n * J(n, x), J(n, -x) = (-1)^n * J(n, x)
117 * Thus, J(-n,x) = J(n,-x)
119 /* if J(n,NaN) is NaN */
120 if (_IEEE && isnan(x)) return x+x;
125 if (n==0) return(j0(x));
126 if (n==1) return(j1(x));
127 sgn = (n&1)&(x < zero); /* even n -- 0, odd n -- sign(x) */
129 if (x == 0 || !finite (x)) /* if x is 0 or inf */
131 else if ((double) n <= x) {
132 /* Safe to use J(n+1,x)=2n/x *J(n,x)-J(n-1,x) */
133 if (_IEEE && x >= 8.148143905337944345e+090) {
136 * Jn(x) = cos(x-(2n+1)*pi/4)*sqrt(2/x*pi)
137 * Yn(x) = sin(x-(2n+1)*pi/4)*sqrt(2/x*pi)
138 * Let s=sin(x), c=cos(x),
139 * xn=x-(2n+1)*pi/4, sqt2 = sqrt(2),then
141 * n sin(xn)*sqt2 cos(xn)*sqt2
142 * ----------------------------------
149 case 0: temp = cos(x)+sin(x); break;
150 case 1: temp = -cos(x)+sin(x); break;
151 case 2: temp = -cos(x)-sin(x); break;
152 case 3: temp = cos(x)-sin(x); break;
154 b = invsqrtpi*temp/sqrt(x);
160 b = b*((double)(i+i)/x) - a; /* avoid underflow */
165 if (x < 1.86264514923095703125e-009) { /* x < 2**-29 */
166 /* x is tiny, return the first Taylor expansion of J(n,x)
167 * J(n,x) = 1/n!*(x/2)^n - ...
169 if (n > 33) /* underflow */
172 temp = x*0.5; b = temp;
173 for (a=one,i=2;i<=n;i++) {
174 a *= (double)i; /* a = n! */
175 b *= temp; /* b = (x/2)^n */
180 /* use backward recurrence */
182 * J(n,x)/J(n-1,x) = ---- ------ ------ .....
183 * 2n - 2(n+1) - 2(n+2)
186 * (for large x) = ---- ------ ------ .....
188 * -- - ------ - ------ -
191 * Let w = 2n/x and h=2/x, then the above quotient
192 * is equal to the continued fraction:
194 * = -----------------------
196 * w - -----------------
201 * To determine how many terms needed, let
202 * Q(0) = w, Q(1) = w(w+h) - 1,
203 * Q(k) = (w+k*h)*Q(k-1) - Q(k-2),
204 * When Q(k) > 1e4 good for single
205 * When Q(k) > 1e9 good for double
206 * When Q(k) > 1e17 good for quadruple
210 double q0,q1,h,tmp; int k,m;
211 w = (n+n)/(double)x; h = 2.0/(double)x;
212 q0 = w; z = w+h; q1 = w*z - 1.0; k=1;
220 for(t=zero, i = 2*(n+k); i>=m; i -= 2) t = one/(i/x-t);
223 /* estimate log((2/x)^n*n!) = n*log(2/x)+n*ln(n)
224 * Hence, if n*(log(2n/x)) > ...
225 * single 8.8722839355e+01
226 * double 7.09782712893383973096e+02
227 * long double 1.1356523406294143949491931077970765006170e+04
228 * then recurrent value may overflow and the result will
229 * likely underflow to zero
233 tmp = tmp*log(fabs(v*tmp));
238 /* scale b to avoid spurious overflow */
239 # if defined(vax) || defined(tahoe)
243 # endif /* defined(vax) || defined(tahoe) */
253 return ((sgn == 1) ? -b : b);
261 /* Y(n,NaN), Y(n, x < 0) is NaN */
262 if (x <= 0 || (_IEEE && x != x))
263 if (_IEEE && x < 0) return zero/zero;
264 else if (x < 0) return (infnan(EDOM));
265 else if (_IEEE) return -one/zero;
266 else return(infnan(-ERANGE));
267 else if (!finite(x)) return(0);
271 sign = 1 - ((n&1)<<2);
273 if (n == 0) return(y0(x));
274 if (n == 1) return(sign*y1(x));
275 if(_IEEE && x >= 8.148143905337944345e+090) { /* x > 2**302 */
277 * Jn(x) = cos(x-(2n+1)*pi/4)*sqrt(2/x*pi)
278 * Yn(x) = sin(x-(2n+1)*pi/4)*sqrt(2/x*pi)
279 * Let s=sin(x), c=cos(x),
280 * xn=x-(2n+1)*pi/4, sqt2 = sqrt(2),then
282 * n sin(xn)*sqt2 cos(xn)*sqt2
283 * ----------------------------------
290 case 0: temp = sin(x)-cos(x); break;
291 case 1: temp = -sin(x)-cos(x); break;
292 case 2: temp = -sin(x)+cos(x); break;
293 case 3: temp = sin(x)+cos(x); break;
295 b = invsqrtpi*temp/sqrt(x);
299 /* quit if b is -inf */
300 for (i = 1; i < n && !finite(b); i++){
302 b = ((double)(i+i)/x)*b - a;
306 if (!_IEEE && !finite(b))
307 return (infnan(-sign * ERANGE));
308 return ((sign > 0) ? b : -b);