1141296Sdas 2141296Sdas/* @(#)e_jn.c 1.4 95/01/18 */ 32116Sjkh/* 42116Sjkh * ==================================================== 52116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 62116Sjkh * 7141296Sdas * Developed at SunSoft, a Sun Microsystems, Inc. business. 82116Sjkh * Permission to use, copy, modify, and distribute this 9141296Sdas * software is freely granted, provided that this notice 102116Sjkh * is preserved. 112116Sjkh * ==================================================== 122116Sjkh */ 132116Sjkh 14176451Sdas#include <sys/cdefs.h> 15176451Sdas__FBSDID("$FreeBSD$"); 162116Sjkh 172116Sjkh/* 182116Sjkh * __ieee754_jn(n, x), __ieee754_yn(n, x) 192116Sjkh * floating point Bessel's function of the 1st and 2nd kind 202116Sjkh * of order n 21141296Sdas * 222116Sjkh * Special cases: 232116Sjkh * y0(0)=y1(0)=yn(n,0) = -inf with division by zero signal; 242116Sjkh * y0(-ve)=y1(-ve)=yn(n,-ve) are NaN with invalid signal. 252116Sjkh * Note 2. About jn(n,x), yn(n,x) 262116Sjkh * For n=0, j0(x) is called, 272116Sjkh * for n=1, j1(x) is called, 282116Sjkh * for n<x, forward recursion us used starting 292116Sjkh * from values of j0(x) and j1(x). 302116Sjkh * for n>x, a continued fraction approximation to 312116Sjkh * j(n,x)/j(n-1,x) is evaluated and then backward 322116Sjkh * recursion is used starting from a supposed value 332116Sjkh * for j(n,x). The resulting value of j(0,x) is 342116Sjkh * compared with the actual value to correct the 352116Sjkh * supposed value of j(n,x). 362116Sjkh * 372116Sjkh * yn(n,x) is similar in all respects, except 382116Sjkh * that forward recursion is used for all 392116Sjkh * values of n>1. 40141296Sdas * 412116Sjkh */ 422116Sjkh 432116Sjkh#include "math.h" 442116Sjkh#include "math_private.h" 452116Sjkh 462116Sjkhstatic const double 472116Sjkhinvsqrtpi= 5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */ 482116Sjkhtwo = 2.00000000000000000000e+00, /* 0x40000000, 0x00000000 */ 492116Sjkhone = 1.00000000000000000000e+00; /* 0x3FF00000, 0x00000000 */ 502116Sjkh 512116Sjkhstatic const double zero = 0.00000000000000000000e+00; 522116Sjkh 5397413Salfreddouble 5497413Salfred__ieee754_jn(int n, double x) 552116Sjkh{ 562116Sjkh int32_t i,hx,ix,lx, sgn; 572116Sjkh double a, b, temp, di; 582116Sjkh double z, w; 592116Sjkh 602116Sjkh /* J(-n,x) = (-1)^n * J(n, x), J(n, -x) = (-1)^n * J(n, x) 612116Sjkh * Thus, J(-n,x) = J(n,-x) 622116Sjkh */ 632116Sjkh EXTRACT_WORDS(hx,lx,x); 642116Sjkh ix = 0x7fffffff&hx; 652116Sjkh /* if J(n,NaN) is NaN */ 662116Sjkh if((ix|((u_int32_t)(lx|-lx))>>31)>0x7ff00000) return x+x; 67141296Sdas if(n<0){ 682116Sjkh n = -n; 692116Sjkh x = -x; 702116Sjkh hx ^= 0x80000000; 712116Sjkh } 722116Sjkh if(n==0) return(__ieee754_j0(x)); 732116Sjkh if(n==1) return(__ieee754_j1(x)); 742116Sjkh sgn = (n&1)&(hx>>31); /* even n -- 0, odd n -- sign(x) */ 752116Sjkh x = fabs(x); 762116Sjkh if((ix|lx)==0||ix>=0x7ff00000) /* if x is 0 or inf */ 772116Sjkh b = zero; 78141296Sdas else if((double)n<=x) { 792116Sjkh /* Safe to use J(n+1,x)=2n/x *J(n,x)-J(n-1,x) */ 802116Sjkh if(ix>=0x52D00000) { /* x > 2**302 */ 81141296Sdas /* (x >> n**2) 822116Sjkh * Jn(x) = cos(x-(2n+1)*pi/4)*sqrt(2/x*pi) 832116Sjkh * Yn(x) = sin(x-(2n+1)*pi/4)*sqrt(2/x*pi) 84141296Sdas * Let s=sin(x), c=cos(x), 852116Sjkh * xn=x-(2n+1)*pi/4, sqt2 = sqrt(2),then 862116Sjkh * 872116Sjkh * n sin(xn)*sqt2 cos(xn)*sqt2 882116Sjkh * ---------------------------------- 892116Sjkh * 0 s-c c+s 902116Sjkh * 1 -s-c -c+s 912116Sjkh * 2 -s+c -c-s 922116Sjkh * 3 s+c c-s 932116Sjkh */ 942116Sjkh switch(n&3) { 952116Sjkh case 0: temp = cos(x)+sin(x); break; 962116Sjkh case 1: temp = -cos(x)+sin(x); break; 972116Sjkh case 2: temp = -cos(x)-sin(x); break; 982116Sjkh case 3: temp = cos(x)-sin(x); break; 992116Sjkh } 1002116Sjkh b = invsqrtpi*temp/sqrt(x); 101141296Sdas } else { 1022116Sjkh a = __ieee754_j0(x); 1032116Sjkh b = __ieee754_j1(x); 1042116Sjkh for(i=1;i<n;i++){ 1052116Sjkh temp = b; 1062116Sjkh b = b*((double)(i+i)/x) - a; /* avoid underflow */ 1072116Sjkh a = temp; 1082116Sjkh } 1092116Sjkh } 1102116Sjkh } else { 1112116Sjkh if(ix<0x3e100000) { /* x < 2**-29 */ 112141296Sdas /* x is tiny, return the first Taylor expansion of J(n,x) 1132116Sjkh * J(n,x) = 1/n!*(x/2)^n - ... 1142116Sjkh */ 1152116Sjkh if(n>33) /* underflow */ 1162116Sjkh b = zero; 1172116Sjkh else { 1182116Sjkh temp = x*0.5; b = temp; 1192116Sjkh for (a=one,i=2;i<=n;i++) { 1202116Sjkh a *= (double)i; /* a = n! */ 1212116Sjkh b *= temp; /* b = (x/2)^n */ 1222116Sjkh } 1232116Sjkh b = b/a; 1242116Sjkh } 1252116Sjkh } else { 1262116Sjkh /* use backward recurrence */ 127141296Sdas /* x x^2 x^2 1282116Sjkh * J(n,x)/J(n-1,x) = ---- ------ ------ ..... 1292116Sjkh * 2n - 2(n+1) - 2(n+2) 1302116Sjkh * 131141296Sdas * 1 1 1 1322116Sjkh * (for large x) = ---- ------ ------ ..... 1332116Sjkh * 2n 2(n+1) 2(n+2) 134141296Sdas * -- - ------ - ------ - 1352116Sjkh * x x x 1362116Sjkh * 1372116Sjkh * Let w = 2n/x and h=2/x, then the above quotient 1382116Sjkh * is equal to the continued fraction: 1392116Sjkh * 1 1402116Sjkh * = ----------------------- 1412116Sjkh * 1 1422116Sjkh * w - ----------------- 1432116Sjkh * 1 1442116Sjkh * w+h - --------- 1452116Sjkh * w+2h - ... 1462116Sjkh * 1472116Sjkh * To determine how many terms needed, let 1482116Sjkh * Q(0) = w, Q(1) = w(w+h) - 1, 1492116Sjkh * Q(k) = (w+k*h)*Q(k-1) - Q(k-2), 150141296Sdas * When Q(k) > 1e4 good for single 151141296Sdas * When Q(k) > 1e9 good for double 152141296Sdas * When Q(k) > 1e17 good for quadruple 1532116Sjkh */ 1542116Sjkh /* determine k */ 1552116Sjkh double t,v; 1562116Sjkh double q0,q1,h,tmp; int32_t k,m; 1572116Sjkh w = (n+n)/(double)x; h = 2.0/(double)x; 1582116Sjkh q0 = w; z = w+h; q1 = w*z - 1.0; k=1; 1592116Sjkh while(q1<1.0e9) { 1602116Sjkh k += 1; z += h; 1612116Sjkh tmp = z*q1 - q0; 1622116Sjkh q0 = q1; 1632116Sjkh q1 = tmp; 1642116Sjkh } 1652116Sjkh m = n+n; 1662116Sjkh for(t=zero, i = 2*(n+k); i>=m; i -= 2) t = one/(i/x-t); 1672116Sjkh a = t; 1682116Sjkh b = one; 1692116Sjkh /* estimate log((2/x)^n*n!) = n*log(2/x)+n*ln(n) 1702116Sjkh * Hence, if n*(log(2n/x)) > ... 1712116Sjkh * single 8.8722839355e+01 1722116Sjkh * double 7.09782712893383973096e+02 1732116Sjkh * long double 1.1356523406294143949491931077970765006170e+04 1748870Srgrimes * then recurrent value may overflow and the result is 1752116Sjkh * likely underflow to zero 1762116Sjkh */ 1772116Sjkh tmp = n; 1782116Sjkh v = two/x; 1792116Sjkh tmp = tmp*__ieee754_log(fabs(v*tmp)); 1802116Sjkh if(tmp<7.09782712893383973096e+02) { 1812116Sjkh for(i=n-1,di=(double)(i+i);i>0;i--){ 1822116Sjkh temp = b; 1832116Sjkh b *= di; 1842116Sjkh b = b/x - a; 1852116Sjkh a = temp; 1862116Sjkh di -= two; 1872116Sjkh } 1882116Sjkh } else { 1892116Sjkh for(i=n-1,di=(double)(i+i);i>0;i--){ 1902116Sjkh temp = b; 1912116Sjkh b *= di; 1922116Sjkh b = b/x - a; 1932116Sjkh a = temp; 1942116Sjkh di -= two; 1952116Sjkh /* scale b to avoid spurious overflow */ 1962116Sjkh if(b>1e100) { 1972116Sjkh a /= b; 1982116Sjkh t /= b; 1992116Sjkh b = one; 2002116Sjkh } 2012116Sjkh } 2022116Sjkh } 203215237Suqs z = __ieee754_j0(x); 204215237Suqs w = __ieee754_j1(x); 205215237Suqs if (fabs(z) >= fabs(w)) 206215237Suqs b = (t*z/b); 207215237Suqs else 208215237Suqs b = (t*w/a); 2092116Sjkh } 2102116Sjkh } 2112116Sjkh if(sgn==1) return -b; else return b; 2122116Sjkh} 2132116Sjkh 21497413Salfreddouble 21597413Salfred__ieee754_yn(int n, double x) 2162116Sjkh{ 2172116Sjkh int32_t i,hx,ix,lx; 2182116Sjkh int32_t sign; 2192116Sjkh double a, b, temp; 2202116Sjkh 2212116Sjkh EXTRACT_WORDS(hx,lx,x); 2222116Sjkh ix = 0x7fffffff&hx; 2232116Sjkh /* if Y(n,NaN) is NaN */ 2242116Sjkh if((ix|((u_int32_t)(lx|-lx))>>31)>0x7ff00000) return x+x; 2252116Sjkh if((ix|lx)==0) return -one/zero; 2262116Sjkh if(hx<0) return zero/zero; 2272116Sjkh sign = 1; 2282116Sjkh if(n<0){ 2292116Sjkh n = -n; 2307658Sbde sign = 1 - ((n&1)<<1); 2312116Sjkh } 2322116Sjkh if(n==0) return(__ieee754_y0(x)); 2332116Sjkh if(n==1) return(sign*__ieee754_y1(x)); 2342116Sjkh if(ix==0x7ff00000) return zero; 2352116Sjkh if(ix>=0x52D00000) { /* x > 2**302 */ 236141296Sdas /* (x >> n**2) 2372116Sjkh * Jn(x) = cos(x-(2n+1)*pi/4)*sqrt(2/x*pi) 2382116Sjkh * Yn(x) = sin(x-(2n+1)*pi/4)*sqrt(2/x*pi) 239141296Sdas * Let s=sin(x), c=cos(x), 2402116Sjkh * xn=x-(2n+1)*pi/4, sqt2 = sqrt(2),then 2412116Sjkh * 2422116Sjkh * n sin(xn)*sqt2 cos(xn)*sqt2 2432116Sjkh * ---------------------------------- 2442116Sjkh * 0 s-c c+s 2452116Sjkh * 1 -s-c -c+s 2462116Sjkh * 2 -s+c -c-s 2472116Sjkh * 3 s+c c-s 2482116Sjkh */ 2492116Sjkh switch(n&3) { 2502116Sjkh case 0: temp = sin(x)-cos(x); break; 2512116Sjkh case 1: temp = -sin(x)-cos(x); break; 2522116Sjkh case 2: temp = -sin(x)+cos(x); break; 2532116Sjkh case 3: temp = sin(x)+cos(x); break; 2542116Sjkh } 2552116Sjkh b = invsqrtpi*temp/sqrt(x); 2562116Sjkh } else { 2572116Sjkh u_int32_t high; 2582116Sjkh a = __ieee754_y0(x); 2592116Sjkh b = __ieee754_y1(x); 2602116Sjkh /* quit if b is -inf */ 2612116Sjkh GET_HIGH_WORD(high,b); 2628870Srgrimes for(i=1;i<n&&high!=0xfff00000;i++){ 2632116Sjkh temp = b; 2642116Sjkh b = ((double)(i+i)/x)*b - a; 2652116Sjkh GET_HIGH_WORD(high,b); 2662116Sjkh a = temp; 2672116Sjkh } 2682116Sjkh } 2692116Sjkh if(sign>0) return b; else return -b; 2702116Sjkh} 271