# e_j1.c   [plain text]

```/* @(#)e_j1.c 5.1 93/09/24 */
/*
* ====================================================
*
* 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_j1.c,v 1.8 1995/05/10 20:45:27 jtc Exp \$";
#endif

/* __ieee754_j1(x), __ieee754_y1(x)
* Bessel function of the first and second kinds of order zero.
* Method -- j1(x):
*	1. For tiny x, we use j1(x) = x/2 - x^3/16 + x^5/384 - ...
*	2. Reduce x to |x| since j1(x)=-j1(-x),  and
*	   for x in (0,2)
*		j1(x) = x/2 + x*z*R0/S0,  where z = x*x;
*	   (precision:  |j1/x - 1/2 - R0/S0 |<2**-61.51 )
*	   for x in (2,inf)
* 		j1(x) = sqrt(2/(pi*x))*(p1(x)*cos(x1)-q1(x)*sin(x1))
* 		y1(x) = sqrt(2/(pi*x))*(p1(x)*sin(x1)+q1(x)*cos(x1))
* 	   where x1 = x-3*pi/4. It is better to compute sin(x1),cos(x1)
*	   as follow:
*		cos(x1) =  cos(x)cos(3pi/4)+sin(x)sin(3pi/4)
*			=  1/sqrt(2) * (sin(x) - cos(x))
*		sin(x1) =  sin(x)cos(3pi/4)-cos(x)sin(3pi/4)
*			= -1/sqrt(2) * (sin(x) + cos(x))
* 	   (To avoid cancellation, use
*		sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
* 	    to compute the worse one.)
*
*	3 Special cases
*		j1(nan)= nan
*		j1(0) = 0
*		j1(inf) = 0
*
* Method -- y1(x):
*	1. screen out x<=0 cases: y1(0)=-inf, y1(x<0)=NaN
*	2. For x<2.
*	   Since
*		y1(x) = 2/pi*(j1(x)*(ln(x/2)+Euler)-1/x-x/2+5/64*x^3-...)
*	   therefore y1(x)-2/pi*j1(x)*ln(x)-1/x is an odd function.
*	   We use the following function to approximate y1,
*		y1(x) = x*U(z)/V(z) + (2/pi)*(j1(x)*ln(x)-1/x), z= x^2
*	   where for x in [0,2] (abs err less than 2**-65.89)
*		U(z) = U0[0] + U0[1]*z + ... + U0[4]*z^4
*		V(z) = 1  + v0[0]*z + ... + v0[4]*z^5
*	   Note: For tiny x, 1/x dominate y1 and hence
*		y1(tiny) = -2/pi/tiny, (choose tiny<2**-54)
*	3. For x>=2.
* 		y1(x) = sqrt(2/(pi*x))*(p1(x)*sin(x1)+q1(x)*cos(x1))
* 	   where x1 = x-3*pi/4. It is better to compute sin(x1),cos(x1)
*	   by method mentioned above.
*/

#include <stddef.h>
#include "math.h"
#include "math_private.h"

#define __ieee754_j1 j1
#define __ieee754_y1 y1
#define __ieee754_log log

#ifdef __STDC__
static double pone(double), qone(double);
#else
static double pone(), qone();
#endif

#ifdef __STDC__
static const double
#else
static double
#endif
huge    = 1e300,
one	= 1.0,
invsqrtpi=  5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
tpi      =  6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
/* R0/S0 on [0,2] */
r00  = -6.25000000000000000000e-02, /* 0xBFB00000, 0x00000000 */
r01  =  1.40705666955189706048e-03, /* 0x3F570D9F, 0x98472C61 */
r02  = -1.59955631084035597520e-05, /* 0xBEF0C5C6, 0xBA169668 */
r03  =  4.96727999609584448412e-08, /* 0x3E6AAAFA, 0x46CA0BD9 */
s01  =  1.91537599538363460805e-02, /* 0x3F939D0B, 0x12637E53 */
s02  =  1.85946785588630915560e-04, /* 0x3F285F56, 0xB9CDF664 */
s03  =  1.17718464042623683263e-06, /* 0x3EB3BFF8, 0x333F8498 */
s04  =  5.04636257076217042715e-09, /* 0x3E35AC88, 0xC97DFF2C */
s05  =  1.23542274426137913908e-11; /* 0x3DAB2ACF, 0xCFB97ED8 */

#ifdef __STDC__
static const double zero    = 0.0;
#else
static double zero    = 0.0;
#endif

#ifdef __STDC__
double __ieee754_j1(double x)
#else
double __ieee754_j1(x)
double x;
#endif
{
double z, s,c,ss,cc,r,u,v,y;
int32_t hx,ix;

GET_HIGH_WORD(hx,x);
ix = hx&0x7fffffff;
if(ix>=0x7ff00000) return one/x;
y = fabs(x);
if(ix >= 0x40000000) {	/* |x| >= 2.0 */
s = sin(y);
c = cos(y);
ss = -s-c;
cc = s-c;
if(ix<0x7fe00000) {  /* make sure y+y not overflow */
z = cos(y+y);
if ((s*c)>zero) cc = z/ss;
else 	    ss = z/cc;
}
/*
* j1(x) = 1/sqrt(pi) * (P(1,x)*cc - Q(1,x)*ss) / sqrt(x)
* y1(x) = 1/sqrt(pi) * (P(1,x)*ss + Q(1,x)*cc) / sqrt(x)
*/
if(ix>0x48000000) z = (invsqrtpi*cc)/sqrt(y);
else {
u = pone(y); v = qone(y);
z = invsqrtpi*(u*cc-v*ss)/sqrt(y);
}
if(hx<0) return -z;
else  	 return  z;
}
if(ix<0x3e400000) {	/* |x|<2**-27 */
if(huge+x>one) return 0.5*x;/* inexact if x!=0 necessary */
}
z = x*x;
r =  z*(r00+z*(r01+z*(r02+z*r03)));
s =  one+z*(s01+z*(s02+z*(s03+z*(s04+z*s05))));
r *= x;
return(x*0.5+r/s);
}

#ifdef __STDC__
static const double U0[5] = {
#else
static double U0[5] = {
#endif
-1.96057090646238940668e-01, /* 0xBFC91866, 0x143CBC8A */
5.04438716639811282616e-02, /* 0x3FA9D3C7, 0x76292CD1 */
-1.91256895875763547298e-03, /* 0xBF5F55E5, 0x4844F50F */
2.35252600561610495928e-05, /* 0x3EF8AB03, 0x8FA6B88E */
-9.19099158039878874504e-08, /* 0xBE78AC00, 0x569105B8 */
};
#ifdef __STDC__
static const double V0[5] = {
#else
static double V0[5] = {
#endif
1.99167318236649903973e-02, /* 0x3F94650D, 0x3F4DA9F0 */
2.02552581025135171496e-04, /* 0x3F2A8C89, 0x6C257764 */
1.35608801097516229404e-06, /* 0x3EB6C05A, 0x894E8CA6 */
6.22741452364621501295e-09, /* 0x3E3ABF1D, 0x5BA69A86 */
1.66559246207992079114e-11, /* 0x3DB25039, 0xDACA772A */
};

#ifdef __STDC__
double __ieee754_y1(double x)
#else
double __ieee754_y1(x)
double x;
#endif
{
double z, s,c,ss,cc,u,v;
int32_t hx,ix,lx;

EXTRACT_WORDS(hx,lx,x);
ix = 0x7fffffff&hx;
/* if Y1(NaN) is NaN, Y1(-inf) is NaN, Y1(inf) is 0 */
if(ix>=0x7ff00000) return  one/(x+x*x);
if((ix|lx)==0) return -one/zero;
if(hx<0) return zero/zero;
if(ix >= 0x40000000) {  /* |x| >= 2.0 */
s = sin(x);
c = cos(x);
ss = -s-c;
cc = s-c;
if(ix<0x7fe00000) {  /* make sure x+x not overflow */
z = cos(x+x);
if ((s*c)>zero) cc = z/ss;
else            ss = z/cc;
}
/* y1(x) = sqrt(2/(pi*x))*(p1(x)*sin(x0)+q1(x)*cos(x0))
* where x0 = x-3pi/4
*      Better formula:
*              cos(x0) = cos(x)cos(3pi/4)+sin(x)sin(3pi/4)
*                      =  1/sqrt(2) * (sin(x) - cos(x))
*              sin(x0) = sin(x)cos(3pi/4)-cos(x)sin(3pi/4)
*                      = -1/sqrt(2) * (cos(x) + sin(x))
* To avoid cancellation, use
*              sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
* to compute the worse one.
*/
if(ix>0x48000000) z = (invsqrtpi*ss)/sqrt(x);
else {
u = pone(x); v = qone(x);
z = invsqrtpi*(u*ss+v*cc)/sqrt(x);
}
return z;
}
if(ix<=0x3c900000) {    /* x < 2**-54 */
return(-tpi/x);
}
z = x*x;
u = U0[0]+z*(U0[1]+z*(U0[2]+z*(U0[3]+z*U0[4])));
v = one+z*(V0[0]+z*(V0[1]+z*(V0[2]+z*(V0[3]+z*V0[4]))));
return(x*(u/v) + tpi*(__ieee754_j1(x)*__ieee754_log(x)-one/x));
}

/* For x >= 8, the asymptotic expansions of pone is
*	1 + 15/128 s^2 - 4725/2^15 s^4 - ...,	where s = 1/x.
* We approximate pone by
* 	pone(x) = 1 + (R/S)
* where  R = pr0 + pr1*s^2 + pr2*s^4 + ... + pr5*s^10
* 	  S = 1 + ps0*s^2 + ... + ps4*s^10
* and
*	| pone(x)-1-R/S | <= 2  ** ( -60.06)
*/

#ifdef __STDC__
static const double pr8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
#else
static double pr8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
#endif
0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
1.17187499999988647970e-01, /* 0x3FBDFFFF, 0xFFFFFCCE */
1.32394806593073575129e+01, /* 0x402A7A9D, 0x357F7FCE */
4.12051854307378562225e+02, /* 0x4079C0D4, 0x652EA590 */
3.87474538913960532227e+03, /* 0x40AE457D, 0xA3A532CC */
7.91447954031891731574e+03, /* 0x40BEEA7A, 0xC32782DD */
};
#ifdef __STDC__
static const double ps8[5] = {
#else
static double ps8[5] = {
#endif
1.14207370375678408436e+02, /* 0x405C8D45, 0x8E656CAC */
3.65093083420853463394e+03, /* 0x40AC85DC, 0x964D274F */
3.69562060269033463555e+04, /* 0x40E20B86, 0x97C5BB7F */
9.76027935934950801311e+04, /* 0x40F7D42C, 0xB28F17BB */
3.08042720627888811578e+04, /* 0x40DE1511, 0x697A0B2D */
};

#ifdef __STDC__
static const double pr5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
#else
static double pr5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
#endif
1.17187493190614097638e-01, /* 0x3FBDFFFF, 0xE2C10043 */
6.80275127868432871736e+00, /* 0x401B3604, 0x6E6315E3 */
1.08308182990189109773e+02, /* 0x405B13B9, 0x452602ED */
5.17636139533199752805e+02, /* 0x40802D16, 0xD052D649 */
5.28715201363337541807e+02, /* 0x408085B8, 0xBB7E0CB7 */
};
#ifdef __STDC__
static const double ps5[5] = {
#else
static double ps5[5] = {
#endif
5.92805987221131331921e+01, /* 0x404DA3EA, 0xA8AF633D */
9.91401418733614377743e+02, /* 0x408EFB36, 0x1B066701 */
5.35326695291487976647e+03, /* 0x40B4E944, 0x5706B6FB */
7.84469031749551231769e+03, /* 0x40BEA4B0, 0xB8A5BB15 */
1.50404688810361062679e+03, /* 0x40978030, 0x036F5E51 */
};

#ifdef __STDC__
static const double pr3[6] = {
#else
static double pr3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
#endif
1.17186865567253592491e-01, /* 0x3FBDFFF5, 0x5B21D17B */
3.51194035591636932736e+01, /* 0x40418F48, 0x9DA6D129 */
9.10550110750781271918e+01, /* 0x4056C385, 0x4D2C1837 */
4.85590685197364919645e+01, /* 0x4048478F, 0x8EA83EE5 */
};
#ifdef __STDC__
static const double ps3[5] = {
#else
static double ps3[5] = {
#endif
3.47913095001251519989e+01, /* 0x40416549, 0xA134069C */
3.36762458747825746741e+02, /* 0x40750C33, 0x07F1A75F */
1.04687139975775130551e+03, /* 0x40905B7C, 0x5037D523 */
8.90811346398256432622e+02, /* 0x408BD67D, 0xA32E31E9 */
1.03787932439639277504e+02, /* 0x4059F26D, 0x7C2EED53 */
};

#ifdef __STDC__
static const double pr2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
#else
static double pr2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
#endif
1.07710830106873743082e-07, /* 0x3E7CE9D4, 0xF65544F4 */
1.17176219462683348094e-01, /* 0x3FBDFF42, 0xBE760D83 */
2.36851496667608785174e+00, /* 0x4002F2B7, 0xF98FAEC0 */
1.22426109148261232917e+01, /* 0x40287C37, 0x7F71A964 */
1.76939711271687727390e+01, /* 0x4031B1A8, 0x177F8EE2 */
5.07352312588818499250e+00, /* 0x40144B49, 0xA574C1FE */
};
#ifdef __STDC__
static const double ps2[5] = {
#else
static double ps2[5] = {
#endif
1.25290227168402751090e+02, /* 0x405F5293, 0x14F92CD5 */
2.32276469057162813669e+02, /* 0x406D08D8, 0xD5A2DBD9 */
1.17679373287147100768e+02, /* 0x405D6B7A, 0xDA1884A9 */
8.36463893371618283368e+00, /* 0x4020BAB1, 0xF44E5192 */
};

#ifdef __STDC__
static double pone(double x)
#else
static double pone(x)
double x;
#endif
{
#ifdef __STDC__
const double *p,*q;
#else
double *p,*q;
#endif
double z,r,s;
int32_t ix;
p = NULL;
q = NULL;
GET_HIGH_WORD(ix,x);
ix &= 0x7fffffff;
if(ix>=0x40200000)     {p = pr8; q= ps8;}
else if(ix>=0x40122E8B){p = pr5; q= ps5;}
else if(ix>=0x4006DB6D){p = pr3; q= ps3;}
else if(ix>=0x40000000){p = pr2; q= ps2;}
z = one/(x*x);
r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*q[4]))));
return one+ r/s;
}

/* For x >= 8, the asymptotic expansions of qone is
*	3/8 s - 105/1024 s^3 - ..., where s = 1/x.
* We approximate pone by
* 	qone(x) = s*(0.375 + (R/S))
* where  R = qr1*s^2 + qr2*s^4 + ... + qr5*s^10
* 	  S = 1 + qs1*s^2 + ... + qs6*s^12
* and
*	| qone(x)/s -0.375-R/S | <= 2  ** ( -61.13)
*/

#ifdef __STDC__
static const double qr8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
#else
static double qr8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
#endif
0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
-1.02539062499992714161e-01, /* 0xBFBA3FFF, 0xFFFFFDF3 */
-1.62717534544589987888e+01, /* 0xC0304591, 0xA26779F7 */
-7.59601722513950107896e+02, /* 0xC087BCD0, 0x53E4B576 */
-1.18498066702429587167e+04, /* 0xC0C724E7, 0x40F87415 */
-4.84385124285750353010e+04, /* 0xC0E7A6D0, 0x65D09C6A */
};
#ifdef __STDC__
static const double qs8[6] = {
#else
static double qs8[6] = {
#endif
1.61395369700722909556e+02, /* 0x40642CA6, 0xDE5BCDE5 */
7.82538599923348465381e+03, /* 0x40BE9162, 0xD0D88419 */
1.33875336287249578163e+05, /* 0x4100579A, 0xB0B75E98 */
7.19657723683240939863e+05, /* 0x4125F653, 0x72869C19 */
-2.94490264303834643215e+05, /* 0xC111F969, 0x0EA5AA18 */
};

#ifdef __STDC__
static const double qr5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
#else
static double qr5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
#endif
-2.08979931141764104297e-11, /* 0xBDB6FA43, 0x1AA1A098 */
-1.02539050241375426231e-01, /* 0xBFBA3FFF, 0xCB597FEF */
-1.83669607474888380239e+02, /* 0xC066F56D, 0x6CA7B9B0 */
-1.37319376065508163265e+03, /* 0xC09574C6, 0x6931734F */
-2.61244440453215656817e+03, /* 0xC0A468E3, 0x88FDA79D */
};
#ifdef __STDC__
static const double qs5[6] = {
#else
static double qs5[6] = {
#endif
8.12765501384335777857e+01, /* 0x405451B2, 0xFF5A11B2 */
1.99179873460485964642e+03, /* 0x409F1F31, 0xE77BF839 */
1.74684851924908907677e+04, /* 0x40D10F1F, 0x0D64CE29 */
2.79480751638918118260e+04, /* 0x40DB4B04, 0xCF7C364B */
-4.71918354795128470869e+03, /* 0xC0B26F2E, 0xFCFFA004 */
};

#ifdef __STDC__
static const double qr3[6] = {
#else
static double qr3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
#endif
-5.07831226461766561369e-09, /* 0xBE35CFA9, 0xD38FC84F */
-1.02537829820837089745e-01, /* 0xBFBA3FEB, 0x51AEED54 */
-4.61011581139473403113e+00, /* 0xC01270C2, 0x3302D9FF */
-5.78472216562783643212e+01, /* 0xC04CEC71, 0xC25D16DA */
-2.28244540737631695038e+02, /* 0xC06C87D3, 0x4718D55F */
-2.19210128478909325622e+02, /* 0xC06B66B9, 0x5F5C1BF6 */
};
#ifdef __STDC__
static const double qs3[6] = {
#else
static double qs3[6] = {
#endif
4.76651550323729509273e+01, /* 0x4047D523, 0xCCD367E4 */
6.73865112676699709482e+02, /* 0x40850EEB, 0xC031EE3E */
3.38015286679526343505e+03, /* 0x40AA684E, 0x448E7C9A */
5.54772909720722782367e+03, /* 0x40B5ABBA, 0xA61D54A6 */
1.90311919338810798763e+03, /* 0x409DBC7A, 0x0DD4DF4B */
-1.35201191444307340817e+02, /* 0xC060E670, 0x290A311F */
};

#ifdef __STDC__
static const double qr2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
#else
static double qr2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
#endif
-1.78381727510958865572e-07, /* 0xBE87F126, 0x44C626D2 */
-1.02517042607985553460e-01, /* 0xBFBA3E8E, 0x9148B010 */
-2.75220568278187460720e+00, /* 0xC0060484, 0x69BB4EDA */
-1.96636162643703720221e+01, /* 0xC033A9E2, 0xC168907F */
-4.23253133372830490089e+01, /* 0xC04529A3, 0xDE104AAA */
-2.13719211703704061733e+01, /* 0xC0355F36, 0x39CF6E52 */
};
#ifdef __STDC__
static const double qs2[6] = {
#else
static double qs2[6] = {
#endif
2.95333629060523854548e+01, /* 0x403D888A, 0x78AE64FF */
2.52981549982190529136e+02, /* 0x406F9F68, 0xDB821CBA */
7.57502834868645436472e+02, /* 0x4087AC05, 0xCE49A0F7 */
7.39393205320467245656e+02, /* 0x40871B25, 0x48D4C029 */
1.55949003336666123687e+02, /* 0x40637E5E, 0x3C3ED8D4 */
-4.95949898822628210127e+00, /* 0xC013D686, 0xE71BE86B */
};

#ifdef __STDC__
static double qone(double x)
#else
static double qone(x)
double x;
#endif
{
#ifdef __STDC__
const double *p,*q;
#else
double *p,*q;
#endif
double  s,r,z;
int32_t ix;
p = NULL;
q = NULL;
GET_HIGH_WORD(ix,x);
ix &= 0x7fffffff;
if(ix>=0x40200000)     {p = qr8; q= qs8;}
else if(ix>=0x40122E8B){p = qr5; q= qs5;}
else if(ix>=0x4006DB6D){p = qr3; q= qs3;}
else if(ix>=0x40000000){p = qr2; q= qs2;}
z = one/(x*x);
r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*(q[4]+z*q[5])))));
return (.375 + r/s)/x;
}
```