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+/* e_jnf.c -- float version of e_jn.c.
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+
+#ifndef lint
+static char rcsid[] = "$Id: e_jnf.c,v 1.2 1994/08/18 23:05:39 jtc Exp $";
+#endif
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+static const float
+#else
+static float
+#endif
+invsqrtpi= 5.6418961287e-01, /* 0x3f106ebb */
+two = 2.0000000000e+00, /* 0x40000000 */
+one = 1.0000000000e+00; /* 0x3F800000 */
+
+#ifdef __STDC__
+static const float zero = 0.0000000000e+00;
+#else
+static float zero = 0.0000000000e+00;
+#endif
+
+#ifdef __STDC__
+ float __ieee754_jnf(int n, float x)
+#else
+ float __ieee754_jnf(n,x)
+ int n; float x;
+#endif
+{
+ int32_t i,hx,ix, sgn;
+ float a, b, temp, di;
+ float 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)
+ */
+ GET_FLOAT_WORD(hx,x);
+ ix = 0x7fffffff&hx;
+ /* if J(n,NaN) is NaN */
+ if(ix>0x7f800000) return x+x;
+ if(n<0){
+ n = -n;
+ x = -x;
+ hx ^= 0x80000000;
+ }
+ if(n==0) return(__ieee754_j0f(x));
+ if(n==1) return(__ieee754_j1f(x));
+ sgn = (n&1)&(hx>>31); /* even n -- 0, odd n -- sign(x) */
+ x = fabsf(x);
+ if(ix==0||ix>=0x7f800000) /* if x is 0 or inf */
+ b = zero;
+ else if((float)n<=x) {
+ /* Safe to use J(n+1,x)=2n/x *J(n,x)-J(n-1,x) */
+ a = __ieee754_j0f(x);
+ b = __ieee754_j1f(x);
+ for(i=1;i<n;i++){
+ temp = b;
+ b = b*((float)(i+i)/x) - a; /* avoid underflow */
+ a = temp;
+ }
+ } else {
+ if(ix<0x30800000) { /* 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*(float)0.5; b = temp;
+ for (a=one,i=2;i<=n;i++) {
+ a *= (float)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 */
+ float t,v;
+ float q0,q1,h,tmp; int32_t k,m;
+ w = (n+n)/(float)x; h = (float)2.0/(float)x;
+ q0 = w; z = w+h; q1 = w*z - (float)1.0; k=1;
+ while(q1<(float)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_logf(fabsf(v*tmp));
+ if(tmp<(float)8.8721679688e+01) {
+ for(i=n-1,di=(float)(i+i);i>0;i--){
+ temp = b;
+ b *= di;
+ b = b/x - a;
+ a = temp;
+ di -= two;
+ }
+ } else {
+ for(i=n-1,di=(float)(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>(float)1e10) {
+ a /= b;
+ t /= b;
+ b = one;
+ }
+ }
+ }
+ b = (t*__ieee754_j0f(x)/b);
+ }
+ }
+ if(sgn==1) return -b; else return b;
+}
+
+#ifdef __STDC__
+ float __ieee754_ynf(int n, float x)
+#else
+ float __ieee754_ynf(n,x)
+ int n; float x;
+#endif
+{
+ int32_t i,hx,ix,ib;
+ int32_t sign;
+ float a, b, temp;
+
+ GET_FLOAT_WORD(hx,x);
+ ix = 0x7fffffff&hx;
+ /* if Y(n,NaN) is NaN */
+ if(ix>0x7f800000) return x+x;
+ if(ix==0) return -one/zero;
+ if(hx<0) return zero/zero;
+ sign = 1;
+ if(n<0){
+ n = -n;
+ sign = 1 - ((n&1)<<2);
+ }
+ if(n==0) return(__ieee754_y0f(x));
+ if(n==1) return(sign*__ieee754_y1f(x));
+ if(ix==0x7f800000) return zero;
+
+ a = __ieee754_y0f(x);
+ b = __ieee754_y1f(x);
+ /* quit if b is -inf */
+ GET_FLOAT_WORD(ib,b);
+ for(i=1;i<n&&ib!=0xff800000;i++){
+ temp = b;
+ b = ((float)(i+i)/x)*b - a;
+ GET_FLOAT_WORD(ib,b);
+ a = temp;
+ }
+ if(sign>0) return b; else return -b;
+}
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