/* $NetBSD: n_jn.c,v 1.8 2018/03/05 23:00:55 christos Exp $ */
/*-
* Copyright (c) 1992, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef lint
#if 0
static char sccsid[] = "@(#)jn.c 8.2 (Berkeley) 11/30/93";
#endif
#endif /* not lint */
/*
* 16 December 1992
* Minor modifications by Peter McIlroy to adapt non-IEEE architecture.
*/
/*
* ====================================================
* Copyright (C) 1992 by Sun Microsystems, Inc.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*
* ******************* WARNING ********************
* This is an alpha version of SunPro's FDLIBM (Freely
* Distributable Math Library) for IEEE double precision
* arithmetic. FDLIBM is a basic math library written
* in C that runs on machines that conform to IEEE
* Standard 754/854. This alpha version is distributed
* for testing purpose. Those who use this software
* should report any bugs to
*
*
[email protected]
*
* -- K.C. Ng, Oct 12, 1992
* ************************************************
*/
/*
* 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 "mathimpl.h"
#include <float.h>
#include <errno.h>
#if defined(__vax__) || defined(tahoe)
#define _IEEE 0
#else
#define _IEEE 1
#define infnan(x) (0.0)
#endif
static const double
#if _IEEE
invsqrtpi= 5.641895835477562869480794515607725858441e-0001,
#endif
two = 2.0,
zero = 0.0,
one = 1.0;
double
jn(int n, double x)
{
int i, sgn;
double a, b, temp;
double z, w;
/* J(-n,x) = (-1)^n * J(n, x), J(n, -x) = (-1)^n * J(n, x)
* Thus, J(-n,x) = J(n,-x)
*/
/* if J(n,NaN) is NaN */
#if _IEEE
if (snan(x)) return x+x;
#endif
if (n<0){
n = -n;
x = -x;
}
if (n==0) return(j0(x));
if (n==1) return(j1(x));
sgn = (n&1)&(x < zero); /* even n -- 0, odd n -- sign(x) */
x = fabs(x);
if (x == 0 || !finite (x)) /* if x is 0 or inf */
b = zero;
else if ((double) n <= x) {
/* Safe to use J(n+1,x)=2n/x *J(n,x)-J(n-1,x) */
#if _IEEE
if (x >= 8.148143905337944345e+090) {
/* x >= 2**302 */
/* (x >> n**2)
* Jn(x) = cos(x-(2n+1)*pi/4)*sqrt(2/x*pi)
* Yn(x) = sin(x-(2n+1)*pi/4)*sqrt(2/x*pi)
* Let s=sin(x), c=cos(x),
* xn=x-(2n+1)*pi/4, sqt2 = sqrt(2),then
*
* n sin(xn)*sqt2 cos(xn)*sqt2
* ----------------------------------
* 0 s-c c+s
* 1 -s-c -c+s
* 2 -s+c -c-s
* 3 s+c c-s
*/
switch(n&3) {
case 0: temp = cos(x)+sin(x); break;
case 1: temp = -cos(x)+sin(x); break;
case 2: temp = -cos(x)-sin(x); break;
case 3: temp = cos(x)-sin(x); break;
}
b = invsqrtpi*temp/sqrt(x);
} else
#endif
{
a = j0(x);
b = j1(x);
for(i=1;i<n;i++){
temp = b;
b = b*((double)(i+i)/x) - a; /* avoid underflow */
a = temp;
}
}
} else {
if (x < 1.86264514923095703125e-009) { /* x < 2**-29 */
/* x is tiny, return the first Taylor expansion of J(n,x)
* J(n,x) = 1/n!*(x/2)^n - ...
*/
if (n > 33) /* underflow */
b = zero;
else {
temp = x*0.5; b = temp;
for (a=one,i=2;i<=n;i++) {
a *= (double)i; /* a = n! */
b *= temp; /* b = (x/2)^n */
}
b = b/a;
}
} else {
/* use backward recurrence */
/* x x^2 x^2
* J(n,x)/J(n-1,x) = ---- ------ ------ .....
* 2n - 2(n+1) - 2(n+2)
*
* 1 1 1
* (for large x) = ---- ------ ------ .....
* 2n 2(n+1) 2(n+2)
* -- - ------ - ------ -
* x x x
*
* Let w = 2n/x and h=2/x, then the above quotient
* is equal to the continued fraction:
* 1
* = -----------------------
* 1
* w - -----------------
* 1
* w+h - ---------
* w+2h - ...
*
* To determine how many terms needed, let
* Q(0) = w, Q(1) = w(w+h) - 1,
* Q(k) = (w+k*h)*Q(k-1) - Q(k-2),
* When Q(k) > 1e4 good for single
* When Q(k) > 1e9 good for double
* When Q(k) > 1e17 good for quadruple
*/
/* determine k */
double t,v;
double q0,q1,h,tmp; int k,m;
w = (n+n)/(double)x; h = 2.0/(double)x;
q0 = w; z = w+h; q1 = w*z - 1.0; k=1;
while (q1<1.0e9) {
k += 1; z += h;
tmp = z*q1 - q0;
q0 = q1;
q1 = tmp;
}
m = n+n;
for(t=zero, i = 2*(n+k); i>=m; i -= 2) t = one/(i/x-t);
a = t;
b = one;
/* estimate log((2/x)^n*n!) = n*log(2/x)+n*ln(n)
* Hence, if n*(log(2n/x)) > ...
* single 8.8722839355e+01
* double 7.09782712893383973096e+02
* long double 1.1356523406294143949491931077970765006170e+04
* then recurrent value may overflow and the result will
* likely underflow to zero
*/
tmp = n;
v = two/x;
tmp = tmp*log(fabs(v*tmp));
for (i=n-1;i>0;i--){
temp = b;
b = ((i+i)/x)*b - a;
a = temp;
/* scale b to avoid spurious overflow */
# if defined(__vax__) || defined(tahoe)
# define BMAX 1e13
# else
# define BMAX 1e100
# endif /* defined(__vax__) || defined(tahoe) */
if (b > BMAX) {
a /= b;
t /= b;
b = one;
}
}
b = (t*j0(x)/b);
}
}
return ((sgn == 1) ? -b : b);
}
double
yn(int n, double x)
{
int i, sign;
double a, b, temp;
/* Y(n,NaN), Y(n, x < 0) is NaN */
if (x <= 0 || (_IEEE && x != x))
if (_IEEE && x < 0) return zero/zero;
else if (x < 0) return (infnan(EDOM));
else if (_IEEE) return -one/zero;
else return(infnan(-ERANGE));
else if (!finite(x)) return(0);
sign = 1;
if (n<0){
n = -n;
sign = 1 - ((n&1)<<2);
}
if (n == 0) return(y0(x));
if (n == 1) return(sign*y1(x));
#if _IEEE
if(x >= 8.148143905337944345e+090) { /* x > 2**302 */
/* (x >> n**2)
* Jn(x) = cos(x-(2n+1)*pi/4)*sqrt(2/x*pi)
* Yn(x) = sin(x-(2n+1)*pi/4)*sqrt(2/x*pi)
* Let s=sin(x), c=cos(x),
* xn=x-(2n+1)*pi/4, sqt2 = sqrt(2),then
*
* n sin(xn)*sqt2 cos(xn)*sqt2
* ----------------------------------
* 0 s-c c+s
* 1 -s-c -c+s
* 2 -s+c -c-s
* 3 s+c c-s
*/
switch (n&3) {
case 0: temp = sin(x)-cos(x); break;
case 1: temp = -sin(x)-cos(x); break;
case 2: temp = -sin(x)+cos(x); break;
case 3: temp = sin(x)+cos(x); break;
}
b = invsqrtpi*temp/sqrt(x);
} else
#endif
{
a = y0(x);
b = y1(x);
/* quit if b is -inf */
for (i = 1; i < n && !finite(b); i++){
temp = b;
b = ((double)(i+i)/x)*b - a;
a = temp;
}
}
if (!_IEEE && !finite(b))
return (infnan(-sign * ERANGE));
return ((sign > 0) ? b : -b);
}
