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authorEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
committerEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
commit7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 (patch)
tree3a7e8476e868ae15f4da1b7ce26b2db6f434468c /libm/e_jn.c
parentc117dd5fb183afb1a4790a6f6110d88704be6bf8 (diff)
downloaduClibc-alpine-7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2.tar.bz2
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Totally rework the math library, this time based on the MacOs X
math library (which is itself based on the math lib from FreeBSD). -Erik
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+/* @(#)e_jn.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * 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.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: e_jn.c,v 1.9 1995/05/10 20:45:34 jtc Exp $";
+#endif
+
+/*
+ * __ieee754_jn(n, x), __ieee754_yn(n, 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 "math_private.h"
+
+#ifdef __STDC__
+static const double
+#else
+static double
+#endif
+invsqrtpi= 5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
+two = 2.00000000000000000000e+00, /* 0x40000000, 0x00000000 */
+one = 1.00000000000000000000e+00; /* 0x3FF00000, 0x00000000 */
+
+#ifdef __STDC__
+static const double zero = 0.00000000000000000000e+00;
+#else
+static double zero = 0.00000000000000000000e+00;
+#endif
+
+#ifdef __STDC__
+ double __ieee754_jn(int n, double x)
+#else
+ double __ieee754_jn(n,x)
+ int n; double x;
+#endif
+{
+ int32_t i,hx,ix,lx, sgn;
+ double a, b, temp, di;
+ 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)
+ */
+ EXTRACT_WORDS(hx,lx,x);
+ ix = 0x7fffffff&hx;
+ /* if J(n,NaN) is NaN */
+ if((ix|((u_int32_t)(lx|-lx))>>31)>0x7ff00000) return x+x;
+ if(n<0){
+ n = -n;
+ x = -x;
+ hx ^= 0x80000000;
+ }
+ if(n==0) return(__ieee754_j0(x));
+ if(n==1) return(__ieee754_j1(x));
+ sgn = (n&1)&(hx>>31); /* even n -- 0, odd n -- sign(x) */
+ x = fabs(x);
+ if((ix|lx)==0||ix>=0x7ff00000) /* 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(ix>=0x52D00000) { /* 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 = __ieee754_j0(x);
+ b = __ieee754_j1(x);
+ for(i=1;i<n;i++){
+ temp = b;
+ b = b*((double)(i+i)/x) - a; /* avoid underflow */
+ a = temp;
+ }
+ }
+ } else {
+ if(ix<0x3e100000) { /* 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; int32_t 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 is
+ * likely underflow to zero
+ */
+ tmp = n;
+ v = two/x;
+ tmp = tmp*__ieee754_log(fabs(v*tmp));
+ if(tmp<7.09782712893383973096e+02) {
+ for(i=n-1,di=(double)(i+i);i>0;i--){
+ temp = b;
+ b *= di;
+ b = b/x - a;
+ a = temp;
+ di -= two;
+ }
+ } else {
+ for(i=n-1,di=(double)(i+i);i>0;i--){
+ temp = b;
+ b *= di;
+ b = b/x - a;
+ a = temp;
+ di -= two;
+ /* scale b to avoid spurious overflow */
+ if(b>1e100) {
+ a /= b;
+ t /= b;
+ b = one;
+ }
+ }
+ }
+ b = (t*__ieee754_j0(x)/b);
+ }
+ }
+ if(sgn==1) return -b; else return b;
+}
+
+#ifdef __STDC__
+ double __ieee754_yn(int n, double x)
+#else
+ double __ieee754_yn(n,x)
+ int n; double x;
+#endif
+{
+ int32_t i,hx,ix,lx;
+ int32_t sign;
+ double a, b, temp;
+
+ EXTRACT_WORDS(hx,lx,x);
+ ix = 0x7fffffff&hx;
+ /* if Y(n,NaN) is NaN */
+ if((ix|((u_int32_t)(lx|-lx))>>31)>0x7ff00000) return x+x;
+ if((ix|lx)==0) return -one/zero;
+ if(hx<0) return zero/zero;
+ sign = 1;
+ if(n<0){
+ n = -n;
+ sign = 1 - ((n&1)<<1);
+ }
+ if(n==0) return(__ieee754_y0(x));
+ if(n==1) return(sign*__ieee754_y1(x));
+ if(ix==0x7ff00000) return zero;
+ if(ix>=0x52D00000) { /* 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 {
+ u_int32_t high;
+ a = __ieee754_y0(x);
+ b = __ieee754_y1(x);
+ /* quit if b is -inf */
+ GET_HIGH_WORD(high,b);
+ for(i=1;i<n&&high!=0xfff00000;i++){
+ temp = b;
+ b = ((double)(i+i)/x)*b - a;
+ GET_HIGH_WORD(high,b);
+ a = temp;
+ }
+ }
+ if(sign>0) return b; else return -b;
+}