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+/*-
+ * 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. All advertising materials mentioning features or use of this software
+ * must display the following acknowledgement:
+ * This product includes software developed by the University of
+ * California, Berkeley and its contributors.
+ * 4. 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
+static char sccsid[] = "@(#)jn.c 8.2 (Berkeley) 11/30/93";
+#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
+ *
+ * fdlibm-comments@sunpro.eng.sun.com
+ *
+ * -- 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 <math.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 double
+invsqrtpi= 5.641895835477562869480794515607725858441e-0001,
+two = 2.0,
+zero = 0.0,
+one = 1.0;
+
+double jn(n,x)
+ 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 && isnan(x)) return x+x;
+ 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 && 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 {
+ 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(n,x)
+ 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 && 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 {
+ 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);
+}
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