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review.blissroms.org / platform_bionic / 1771a33d11a24f1c47b1ef75e3726c5d9e751f5b / . / libm / src / e_j0.c
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The Android Open Source Project1dc9e472009-03-03 19:28:35 -0800[diff] [blame]1
2/* @(#)e_j0.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14#ifndef lint
15static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_j0.c,v 1.8 2005/02/04 18:26:05 das Exp $";
16#endif
17
18/* __ieee754_j0(x), __ieee754_y0(x)
19 * Bessel function of the first and second kinds of order zero.
20 * Method -- j0(x):
21 * 1. For tiny x, we use j0(x) = 1 - x^2/4 + x^4/64 - ...
22 * 2. Reduce x to |x| since j0(x)=j0(-x), and
23 * for x in (0,2)
24 * j0(x) = 1-z/4+ z^2*R0/S0, where z = x*x;
25 * (precision: |j0-1+z/4-z^2R0/S0 |<2**-63.67 )
26 * for x in (2,inf)
27 * j0(x) = sqrt(2/(pi*x))*(p0(x)*cos(x0)-q0(x)*sin(x0))
28 * where x0 = x-pi/4. It is better to compute sin(x0),cos(x0)
29 * as follow:
30 * cos(x0) = cos(x)cos(pi/4)+sin(x)sin(pi/4)
31 * = 1/sqrt(2) * (cos(x) + sin(x))
32 * sin(x0) = sin(x)cos(pi/4)-cos(x)sin(pi/4)
33 * = 1/sqrt(2) * (sin(x) - cos(x))
34 * (To avoid cancellation, use
35 * sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
36 * to compute the worse one.)
37 *
38 * 3 Special cases
39 * j0(nan)= nan
40 * j0(0) = 1
41 * j0(inf) = 0
42 *
43 * Method -- y0(x):
44 * 1. For x<2.
45 * Since
46 * y0(x) = 2/pi*(j0(x)*(ln(x/2)+Euler) + x^2/4 - ...)
47 * therefore y0(x)-2/pi*j0(x)*ln(x) is an even function.
48 * We use the following function to approximate y0,
49 * y0(x) = U(z)/V(z) + (2/pi)*(j0(x)*ln(x)), z= x^2
50 * where
51 * U(z) = u00 + u01*z + ... + u06*z^6
52 * V(z) = 1 + v01*z + ... + v04*z^4
53 * with absolute approximation error bounded by 2**-72.
54 * Note: For tiny x, U/V = u0 and j0(x)~1, hence
55 * y0(tiny) = u0 + (2/pi)*ln(tiny), (choose tiny<2**-27)
56 * 2. For x>=2.
57 * y0(x) = sqrt(2/(pi*x))*(p0(x)*cos(x0)+q0(x)*sin(x0))
58 * where x0 = x-pi/4. It is better to compute sin(x0),cos(x0)
59 * by the method mentioned above.
60 * 3. Special cases: y0(0)=-inf, y0(x<0)=NaN, y0(inf)=0.
61 */
62
63#include "math.h"
64#include "math_private.h"
65
66static double pzero(double), qzero(double);
67
68static const double
69huge = 1e300,
70one = 1.0,
71invsqrtpi= 5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
72tpi = 6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
73 /* R0/S0 on [0, 2.00] */
74R02 = 1.56249999999999947958e-02, /* 0x3F8FFFFF, 0xFFFFFFFD */
75R03 = -1.89979294238854721751e-04, /* 0xBF28E6A5, 0xB61AC6E9 */
76R04 = 1.82954049532700665670e-06, /* 0x3EBEB1D1, 0x0C503919 */
77R05 = -4.61832688532103189199e-09, /* 0xBE33D5E7, 0x73D63FCE */
78S01 = 1.56191029464890010492e-02, /* 0x3F8FFCE8, 0x82C8C2A4 */
79S02 = 1.16926784663337450260e-04, /* 0x3F1EA6D2, 0xDD57DBF4 */
80S03 = 5.13546550207318111446e-07, /* 0x3EA13B54, 0xCE84D5A9 */
81S04 = 1.16614003333790000205e-09; /* 0x3E1408BC, 0xF4745D8F */
82
83static const double zero = 0.0;
84
85double
86__ieee754_j0(double x)
87{
88 double z, s,c,ss,cc,r,u,v;
89 int32_t hx,ix;
90
91 GET_HIGH_WORD(hx,x);
92 ix = hx&0x7fffffff;
93 if(ix>=0x7ff00000) return one/(x*x);
94 x = fabs(x);
95 if(ix >= 0x40000000) { /* |x| >= 2.0 */
96 s = sin(x);
97 c = cos(x);
98 ss = s-c;
99 cc = s+c;
100 if(ix<0x7fe00000) { /* make sure x+x not overflow */
101 z = -cos(x+x);
102 if ((s*c)<zero) cc = z/ss;
103 else ss = z/cc;
104 }
105 /*
106 * j0(x) = 1/sqrt(pi) * (P(0,x)*cc - Q(0,x)*ss) / sqrt(x)
107 * y0(x) = 1/sqrt(pi) * (P(0,x)*ss + Q(0,x)*cc) / sqrt(x)
108 */
109 if(ix>0x48000000) z = (invsqrtpi*cc)/sqrt(x);
110 else {
111 u = pzero(x); v = qzero(x);
112 z = invsqrtpi*(u*cc-v*ss)/sqrt(x);
113 }
114 return z;
115 }
116 if(ix<0x3f200000) { /* |x| < 2**-13 */
117 if(huge+x>one) { /* raise inexact if x != 0 */
118 if(ix<0x3e400000) return one; /* |x|<2**-27 */
119 else return one - 0.25*x*x;
120 }
121 }
122 z = x*x;
123 r = z*(R02+z*(R03+z*(R04+z*R05)));
124 s = one+z*(S01+z*(S02+z*(S03+z*S04)));
125 if(ix < 0x3FF00000) { /* |x| < 1.00 */
126 return one + z*(-0.25+(r/s));
127 } else {
128 u = 0.5*x;
129 return((one+u)*(one-u)+z*(r/s));
130 }
131}
132
133static const double
134u00 = -7.38042951086872317523e-02, /* 0xBFB2E4D6, 0x99CBD01F */
135u01 = 1.76666452509181115538e-01, /* 0x3FC69D01, 0x9DE9E3FC */
136u02 = -1.38185671945596898896e-02, /* 0xBF8C4CE8, 0xB16CFA97 */
137u03 = 3.47453432093683650238e-04, /* 0x3F36C54D, 0x20B29B6B */
138u04 = -3.81407053724364161125e-06, /* 0xBECFFEA7, 0x73D25CAD */
139u05 = 1.95590137035022920206e-08, /* 0x3E550057, 0x3B4EABD4 */
140u06 = -3.98205194132103398453e-11, /* 0xBDC5E43D, 0x693FB3C8 */
141v01 = 1.27304834834123699328e-02, /* 0x3F8A1270, 0x91C9C71A */
142v02 = 7.60068627350353253702e-05, /* 0x3F13ECBB, 0xF578C6C1 */
143v03 = 2.59150851840457805467e-07, /* 0x3E91642D, 0x7FF202FD */
144v04 = 4.41110311332675467403e-10; /* 0x3DFE5018, 0x3BD6D9EF */
145
146double
147__ieee754_y0(double x)
148{
149 double z, s,c,ss,cc,u,v;
150 int32_t hx,ix,lx;
151
152 EXTRACT_WORDS(hx,lx,x);
153 ix = 0x7fffffff&hx;
154 /* Y0(NaN) is NaN, y0(-inf) is Nan, y0(inf) is 0 */
155 if(ix>=0x7ff00000) return one/(x+x*x);
156 if((ix|lx)==0) return -one/zero;
157 if(hx<0) return zero/zero;
158 if(ix >= 0x40000000) { /* |x| >= 2.0 */
159 /* y0(x) = sqrt(2/(pi*x))*(p0(x)*sin(x0)+q0(x)*cos(x0))
160 * where x0 = x-pi/4
161 * Better formula:
162 * cos(x0) = cos(x)cos(pi/4)+sin(x)sin(pi/4)
163 * = 1/sqrt(2) * (sin(x) + cos(x))
164 * sin(x0) = sin(x)cos(3pi/4)-cos(x)sin(3pi/4)
165 * = 1/sqrt(2) * (sin(x) - cos(x))
166 * To avoid cancellation, use
167 * sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
168 * to compute the worse one.
169 */
170 s = sin(x);
171 c = cos(x);
172 ss = s-c;
173 cc = s+c;
174 /*
175 * j0(x) = 1/sqrt(pi) * (P(0,x)*cc - Q(0,x)*ss) / sqrt(x)
176 * y0(x) = 1/sqrt(pi) * (P(0,x)*ss + Q(0,x)*cc) / sqrt(x)
177 */
178 if(ix<0x7fe00000) { /* make sure x+x not overflow */
179 z = -cos(x+x);
180 if ((s*c)<zero) cc = z/ss;
181 else ss = z/cc;
182 }
183 if(ix>0x48000000) z = (invsqrtpi*ss)/sqrt(x);
184 else {
185 u = pzero(x); v = qzero(x);
186 z = invsqrtpi*(u*ss+v*cc)/sqrt(x);
187 }
188 return z;
189 }
190 if(ix<=0x3e400000) { /* x < 2**-27 */
191 return(u00 + tpi*__ieee754_log(x));
192 }
193 z = x*x;
194 u = u00+z*(u01+z*(u02+z*(u03+z*(u04+z*(u05+z*u06)))));
195 v = one+z*(v01+z*(v02+z*(v03+z*v04)));
196 return(u/v + tpi*(__ieee754_j0(x)*__ieee754_log(x)));
197}
198
199/* The asymptotic expansions of pzero is
200 * 1 - 9/128 s^2 + 11025/98304 s^4 - ..., where s = 1/x.
201 * For x >= 2, We approximate pzero by
202 * pzero(x) = 1 + (R/S)
203 * where R = pR0 + pR1*s^2 + pR2*s^4 + ... + pR5*s^10
204 * S = 1 + pS0*s^2 + ... + pS4*s^10
205 * and
206 * | pzero(x)-1-R/S | <= 2 ** ( -60.26)
207 */
208static const double pR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
209 0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
210 -7.03124999999900357484e-02, /* 0xBFB1FFFF, 0xFFFFFD32 */
211 -8.08167041275349795626e+00, /* 0xC02029D0, 0xB44FA779 */
212 -2.57063105679704847262e+02, /* 0xC0701102, 0x7B19E863 */
213 -2.48521641009428822144e+03, /* 0xC0A36A6E, 0xCD4DCAFC */
214 -5.25304380490729545272e+03, /* 0xC0B4850B, 0x36CC643D */
215};
216static const double pS8[5] = {
217 1.16534364619668181717e+02, /* 0x405D2233, 0x07A96751 */
218 3.83374475364121826715e+03, /* 0x40ADF37D, 0x50596938 */
219 4.05978572648472545552e+04, /* 0x40E3D2BB, 0x6EB6B05F */
220 1.16752972564375915681e+05, /* 0x40FC810F, 0x8F9FA9BD */
221 4.76277284146730962675e+04, /* 0x40E74177, 0x4F2C49DC */
222};
223
224static const double pR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
225 -1.14125464691894502584e-11, /* 0xBDA918B1, 0x47E495CC */
226 -7.03124940873599280078e-02, /* 0xBFB1FFFF, 0xE69AFBC6 */
227 -4.15961064470587782438e+00, /* 0xC010A370, 0xF90C6BBF */
228 -6.76747652265167261021e+01, /* 0xC050EB2F, 0x5A7D1783 */
229 -3.31231299649172967747e+02, /* 0xC074B3B3, 0x6742CC63 */
230 -3.46433388365604912451e+02, /* 0xC075A6EF, 0x28A38BD7 */
231};
232static const double pS5[5] = {
233 6.07539382692300335975e+01, /* 0x404E6081, 0x0C98C5DE */
234 1.05125230595704579173e+03, /* 0x40906D02, 0x5C7E2864 */
235 5.97897094333855784498e+03, /* 0x40B75AF8, 0x8FBE1D60 */
236 9.62544514357774460223e+03, /* 0x40C2CCB8, 0xFA76FA38 */
237 2.40605815922939109441e+03, /* 0x40A2CC1D, 0xC70BE864 */
238};
239
240static const double pR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
241 -2.54704601771951915620e-09, /* 0xBE25E103, 0x6FE1AA86 */
242 -7.03119616381481654654e-02, /* 0xBFB1FFF6, 0xF7C0E24B */
243 -2.40903221549529611423e+00, /* 0xC00345B2, 0xAEA48074 */
244 -2.19659774734883086467e+01, /* 0xC035F74A, 0x4CB94E14 */
245 -5.80791704701737572236e+01, /* 0xC04D0A22, 0x420A1A45 */
246 -3.14479470594888503854e+01, /* 0xC03F72AC, 0xA892D80F */
247};
248static const double pS3[5] = {
249 3.58560338055209726349e+01, /* 0x4041ED92, 0x84077DD3 */
250 3.61513983050303863820e+02, /* 0x40769839, 0x464A7C0E */
251 1.19360783792111533330e+03, /* 0x4092A66E, 0x6D1061D6 */
252 1.12799679856907414432e+03, /* 0x40919FFC, 0xB8C39B7E */
253 1.73580930813335754692e+02, /* 0x4065B296, 0xFC379081 */
254};
255
256static const double pR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
257 -8.87534333032526411254e-08, /* 0xBE77D316, 0xE927026D */
258 -7.03030995483624743247e-02, /* 0xBFB1FF62, 0x495E1E42 */
259 -1.45073846780952986357e+00, /* 0xBFF73639, 0x8A24A843 */
260 -7.63569613823527770791e+00, /* 0xC01E8AF3, 0xEDAFA7F3 */
261 -1.11931668860356747786e+01, /* 0xC02662E6, 0xC5246303 */
262 -3.23364579351335335033e+00, /* 0xC009DE81, 0xAF8FE70F */
263};
264static const double pS2[5] = {
265 2.22202997532088808441e+01, /* 0x40363865, 0x908B5959 */
266 1.36206794218215208048e+02, /* 0x4061069E, 0x0EE8878F */
267 2.70470278658083486789e+02, /* 0x4070E786, 0x42EA079B */
268 1.53875394208320329881e+02, /* 0x40633C03, 0x3AB6FAFF */
269 1.46576176948256193810e+01, /* 0x402D50B3, 0x44391809 */
270};
271
272 static double pzero(double x)
273{
274 const double *p,*q;
275 double z,r,s;
276 int32_t ix;
277 GET_HIGH_WORD(ix,x);
278 ix &= 0x7fffffff;
279 if(ix>=0x40200000) {p = pR8; q= pS8;}
280 else if(ix>=0x40122E8B){p = pR5; q= pS5;}
281 else if(ix>=0x4006DB6D){p = pR3; q= pS3;}
282 else if(ix>=0x40000000){p = pR2; q= pS2;}
283 z = one/(x*x);
284 r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
285 s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*q[4]))));
286 return one+ r/s;
287}
288
289
290/* For x >= 8, the asymptotic expansions of qzero is
291 * -1/8 s + 75/1024 s^3 - ..., where s = 1/x.
292 * We approximate pzero by
293 * qzero(x) = s*(-1.25 + (R/S))
294 * where R = qR0 + qR1*s^2 + qR2*s^4 + ... + qR5*s^10
295 * S = 1 + qS0*s^2 + ... + qS5*s^12
296 * and
297 * | qzero(x)/s +1.25-R/S | <= 2 ** ( -61.22)
298 */
299static const double qR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
300 0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
301 7.32421874999935051953e-02, /* 0x3FB2BFFF, 0xFFFFFE2C */
302 1.17682064682252693899e+01, /* 0x40278952, 0x5BB334D6 */
303 5.57673380256401856059e+02, /* 0x40816D63, 0x15301825 */
304 8.85919720756468632317e+03, /* 0x40C14D99, 0x3E18F46D */
305 3.70146267776887834771e+04, /* 0x40E212D4, 0x0E901566 */
306};
307static const double qS8[6] = {
308 1.63776026895689824414e+02, /* 0x406478D5, 0x365B39BC */
309 8.09834494656449805916e+03, /* 0x40BFA258, 0x4E6B0563 */
310 1.42538291419120476348e+05, /* 0x41016652, 0x54D38C3F */
311 8.03309257119514397345e+05, /* 0x412883DA, 0x83A52B43 */
312 8.40501579819060512818e+05, /* 0x4129A66B, 0x28DE0B3D */
313 -3.43899293537866615225e+05, /* 0xC114FD6D, 0x2C9530C5 */
314};
315
316static const double qR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
317 1.84085963594515531381e-11, /* 0x3DB43D8F, 0x29CC8CD9 */
318 7.32421766612684765896e-02, /* 0x3FB2BFFF, 0xD172B04C */
319 5.83563508962056953777e+00, /* 0x401757B0, 0xB9953DD3 */
320 1.35111577286449829671e+02, /* 0x4060E392, 0x0A8788E9 */
321 1.02724376596164097464e+03, /* 0x40900CF9, 0x9DC8C481 */
322 1.98997785864605384631e+03, /* 0x409F17E9, 0x53C6E3A6 */
323};
324static const double qS5[6] = {
325 8.27766102236537761883e+01, /* 0x4054B1B3, 0xFB5E1543 */
326 2.07781416421392987104e+03, /* 0x40A03BA0, 0xDA21C0CE */
327 1.88472887785718085070e+04, /* 0x40D267D2, 0x7B591E6D */
328 5.67511122894947329769e+04, /* 0x40EBB5E3, 0x97E02372 */
329 3.59767538425114471465e+04, /* 0x40E19118, 0x1F7A54A0 */
330 -5.35434275601944773371e+03, /* 0xC0B4EA57, 0xBEDBC609 */
331};
332
333static const double qR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
334 4.37741014089738620906e-09, /* 0x3E32CD03, 0x6ADECB82 */
335 7.32411180042911447163e-02, /* 0x3FB2BFEE, 0x0E8D0842 */
336 3.34423137516170720929e+00, /* 0x400AC0FC, 0x61149CF5 */
337 4.26218440745412650017e+01, /* 0x40454F98, 0x962DAEDD */
338 1.70808091340565596283e+02, /* 0x406559DB, 0xE25EFD1F */
339 1.66733948696651168575e+02, /* 0x4064D77C, 0x81FA21E0 */
340};
341static const double qS3[6] = {
342 4.87588729724587182091e+01, /* 0x40486122, 0xBFE343A6 */
343 7.09689221056606015736e+02, /* 0x40862D83, 0x86544EB3 */
344 3.70414822620111362994e+03, /* 0x40ACF04B, 0xE44DFC63 */
345 6.46042516752568917582e+03, /* 0x40B93C6C, 0xD7C76A28 */
346 2.51633368920368957333e+03, /* 0x40A3A8AA, 0xD94FB1C0 */
347 -1.49247451836156386662e+02, /* 0xC062A7EB, 0x201CF40F */
348};
349
350static const double qR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
351 1.50444444886983272379e-07, /* 0x3E84313B, 0x54F76BDB */
352 7.32234265963079278272e-02, /* 0x3FB2BEC5, 0x3E883E34 */
353 1.99819174093815998816e+00, /* 0x3FFFF897, 0xE727779C */
354 1.44956029347885735348e+01, /* 0x402CFDBF, 0xAAF96FE5 */
355 3.16662317504781540833e+01, /* 0x403FAA8E, 0x29FBDC4A */
356 1.62527075710929267416e+01, /* 0x403040B1, 0x71814BB4 */
357};
358static const double qS2[6] = {
359 3.03655848355219184498e+01, /* 0x403E5D96, 0xF7C07AED */
360 2.69348118608049844624e+02, /* 0x4070D591, 0xE4D14B40 */
361 8.44783757595320139444e+02, /* 0x408A6645, 0x22B3BF22 */
362 8.82935845112488550512e+02, /* 0x408B977C, 0x9C5CC214 */
363 2.12666388511798828631e+02, /* 0x406A9553, 0x0E001365 */
364 -5.31095493882666946917e+00, /* 0xC0153E6A, 0xF8B32931 */
365};
366
367 static double qzero(double x)
368{
369 const double *p,*q;
370 double s,r,z;
371 int32_t ix;
372 GET_HIGH_WORD(ix,x);
373 ix &= 0x7fffffff;
374 if(ix>=0x40200000) {p = qR8; q= qS8;}
375 else if(ix>=0x40122E8B){p = qR5; q= qS5;}
376 else if(ix>=0x4006DB6D){p = qR3; q= qS3;}
377 else if(ix>=0x40000000){p = qR2; q= qS2;}
378 z = one/(x*x);
379 r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
380 s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*(q[4]+z*q[5])))));
381 return (-.125 + r/s)/x;
382}