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1/* @(#)e_j0.c 5.1 93/09/24 */
2/*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13#if defined(LIBM_SCCS) && !defined(lint)
14static char rcsid[] = "$NetBSD: e_j0.c,v 1.8 1995/05/10 20:45:23 jtc Exp $";
15#endif
16
17/* __ieee754_j0(x), __ieee754_y0(x)
18 * Bessel function of the first and second kinds of order zero.
19 * Method -- j0(x):
20 * 1. For tiny x, we use j0(x) = 1 - x^2/4 + x^4/64 - ...
21 * 2. Reduce x to |x| since j0(x)=j0(-x), and
22 * for x in (0,2)
23 * j0(x) = 1-z/4+ z^2*R0/S0, where z = x*x;
24 * (precision: |j0-1+z/4-z^2R0/S0 |<2**-63.67 )
25 * for x in (2,inf)
26 * j0(x) = sqrt(2/(pi*x))*(p0(x)*cos(x0)-q0(x)*sin(x0))
27 * where x0 = x-pi/4. It is better to compute sin(x0),cos(x0)
28 * as follow:
29 * cos(x0) = cos(x)cos(pi/4)+sin(x)sin(pi/4)
30 * = 1/sqrt(2) * (cos(x) + sin(x))
31 * sin(x0) = sin(x)cos(pi/4)-cos(x)sin(pi/4)
32 * = 1/sqrt(2) * (sin(x) - cos(x))
33 * (To avoid cancellation, use
34 * sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
35 * to compute the worse one.)
36 *
37 * 3 Special cases
38 * j0(nan)= nan
39 * j0(0) = 1
40 * j0(inf) = 0
41 *
42 * Method -- y0(x):
43 * 1. For x<2.
44 * Since
45 * y0(x) = 2/pi*(j0(x)*(ln(x/2)+Euler) + x^2/4 - ...)
46 * therefore y0(x)-2/pi*j0(x)*ln(x) is an even function.
47 * We use the following function to approximate y0,
48 * y0(x) = U(z)/V(z) + (2/pi)*(j0(x)*ln(x)), z= x^2
49 * where
50 * U(z) = u00 + u01*z + ... + u06*z^6
51 * V(z) = 1 + v01*z + ... + v04*z^4
52 * with absolute approximation error bounded by 2**-72.
53 * Note: For tiny x, U/V = u0 and j0(x)~1, hence
54 * y0(tiny) = u0 + (2/pi)*ln(tiny), (choose tiny<2**-27)
55 * 2. For x>=2.
56 * y0(x) = sqrt(2/(pi*x))*(p0(x)*cos(x0)+q0(x)*sin(x0))
57 * where x0 = x-pi/4. It is better to compute sin(x0),cos(x0)
58 * by the method mentioned above.
59 * 3. Special cases: y0(0)=-inf, y0(x<0)=NaN, y0(inf)=0.
60 */
61
62#include <stddef.h>
63#include "math.h"
64#include "math_private.h"
65
66#define __ieee754_j0 j0
67#define __ieee754_y0 y0
68#define __ieee754_log log
69
70#ifdef __STDC__
71static double pzero(double), qzero(double);
72#else
73static double pzero(), qzero();
74#endif
75
76#ifdef __STDC__
77static const double
78#else
79static double
80#endif
81huge = 1e300,
82one = 1.0,
83invsqrtpi= 5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
84tpi = 6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
85 /* R0/S0 on [0, 2.00] */
86R02 = 1.56249999999999947958e-02, /* 0x3F8FFFFF, 0xFFFFFFFD */
87R03 = -1.89979294238854721751e-04, /* 0xBF28E6A5, 0xB61AC6E9 */
88R04 = 1.82954049532700665670e-06, /* 0x3EBEB1D1, 0x0C503919 */
89R05 = -4.61832688532103189199e-09, /* 0xBE33D5E7, 0x73D63FCE */
90S01 = 1.56191029464890010492e-02, /* 0x3F8FFCE8, 0x82C8C2A4 */
91S02 = 1.16926784663337450260e-04, /* 0x3F1EA6D2, 0xDD57DBF4 */
92S03 = 5.13546550207318111446e-07, /* 0x3EA13B54, 0xCE84D5A9 */
93S04 = 1.16614003333790000205e-09; /* 0x3E1408BC, 0xF4745D8F */
94
95#ifdef __STDC__
96static const double zero = 0.0;
97#else
98static double zero = 0.0;
99#endif
100
101#ifdef __STDC__
102 double __ieee754_j0(double x)
103#else
104 double __ieee754_j0(x)
105 double x;
106#endif
107{
108 double z, s,c,ss,cc,r,u,v;
109 int32_t hx,ix;
110
111 GET_HIGH_WORD(hx,x);
112 ix = hx&0x7fffffff;
113 if(ix>=0x7ff00000) return one/(x*x);
114 x = fabs(x);
115 if(ix >= 0x40000000) { /* |x| >= 2.0 */
116 s = sin(x);
117 c = cos(x);
118 ss = s-c;
119 cc = s+c;
120 if(ix<0x7fe00000) { /* make sure x+x not overflow */
121 z = -cos(x+x);
122 if ((s*c)<zero) cc = z/ss;
123 else ss = z/cc;
124 }
125 /*
126 * j0(x) = 1/sqrt(pi) * (P(0,x)*cc - Q(0,x)*ss) / sqrt(x)
127 * y0(x) = 1/sqrt(pi) * (P(0,x)*ss + Q(0,x)*cc) / sqrt(x)
128 */
129 if(ix>0x48000000) z = (invsqrtpi*cc)/sqrt(x);
130 else {
131 u = pzero(x); v = qzero(x);
132 z = invsqrtpi*(u*cc-v*ss)/sqrt(x);
133 }
134 return z;
135 }
136 if(ix<0x3f200000) { /* |x| < 2**-13 */
137 if(huge+x>one) { /* raise inexact if x != 0 */
138 if(ix<0x3e400000) return one; /* |x|<2**-27 */
139 else return one - 0.25*x*x;
140 }
141 }
142 z = x*x;
143 r = z*(R02+z*(R03+z*(R04+z*R05)));
144 s = one+z*(S01+z*(S02+z*(S03+z*S04)));
145 if(ix < 0x3FF00000) { /* |x| < 1.00 */
146 return one + z*(-0.25+(r/s));
147 } else {
148 u = 0.5*x;
149 return((one+u)*(one-u)+z*(r/s));
150 }
151}
152
153#ifdef __STDC__
154static const double
155#else
156static double
157#endif
158u00 = -7.38042951086872317523e-02, /* 0xBFB2E4D6, 0x99CBD01F */
159u01 = 1.76666452509181115538e-01, /* 0x3FC69D01, 0x9DE9E3FC */
160u02 = -1.38185671945596898896e-02, /* 0xBF8C4CE8, 0xB16CFA97 */
161u03 = 3.47453432093683650238e-04, /* 0x3F36C54D, 0x20B29B6B */
162u04 = -3.81407053724364161125e-06, /* 0xBECFFEA7, 0x73D25CAD */
163u05 = 1.95590137035022920206e-08, /* 0x3E550057, 0x3B4EABD4 */
164u06 = -3.98205194132103398453e-11, /* 0xBDC5E43D, 0x693FB3C8 */
165v01 = 1.27304834834123699328e-02, /* 0x3F8A1270, 0x91C9C71A */
166v02 = 7.60068627350353253702e-05, /* 0x3F13ECBB, 0xF578C6C1 */
167v03 = 2.59150851840457805467e-07, /* 0x3E91642D, 0x7FF202FD */
168v04 = 4.41110311332675467403e-10; /* 0x3DFE5018, 0x3BD6D9EF */
169
170#ifdef __STDC__
171 double __ieee754_y0(double x)
172#else
173 double __ieee754_y0(x)
174 double x;
175#endif
176{
177 double z, s,c,ss,cc,u,v;
178 int32_t hx,ix,lx;
179
180 EXTRACT_WORDS(hx,lx,x);
181 ix = 0x7fffffff&hx;
182 /* Y0(NaN) is NaN, y0(-inf) is Nan, y0(inf) is 0 */
183 if(ix>=0x7ff00000) return one/(x+x*x);
184 if((ix|lx)==0) return -one/zero;
185 if(hx<0) return zero/zero;
186 if(ix >= 0x40000000) { /* |x| >= 2.0 */
187 /* y0(x) = sqrt(2/(pi*x))*(p0(x)*sin(x0)+q0(x)*cos(x0))
188 * where x0 = x-pi/4
189 * Better formula:
190 * cos(x0) = cos(x)cos(pi/4)+sin(x)sin(pi/4)
191 * = 1/sqrt(2) * (sin(x) + cos(x))
192 * sin(x0) = sin(x)cos(3pi/4)-cos(x)sin(3pi/4)
193 * = 1/sqrt(2) * (sin(x) - cos(x))
194 * To avoid cancellation, use
195 * sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
196 * to compute the worse one.
197 */
198 s = sin(x);
199 c = cos(x);
200 ss = s-c;
201 cc = s+c;
202 /*
203 * j0(x) = 1/sqrt(pi) * (P(0,x)*cc - Q(0,x)*ss) / sqrt(x)
204 * y0(x) = 1/sqrt(pi) * (P(0,x)*ss + Q(0,x)*cc) / sqrt(x)
205 */
206 if(ix<0x7fe00000) { /* make sure x+x not overflow */
207 z = -cos(x+x);
208 if ((s*c)<zero) cc = z/ss;
209 else ss = z/cc;
210 }
211 if(ix>0x48000000) z = (invsqrtpi*ss)/sqrt(x);
212 else {
213 u = pzero(x); v = qzero(x);
214 z = invsqrtpi*(u*ss+v*cc)/sqrt(x);
215 }
216 return z;
217 }
218 if(ix<=0x3e400000) { /* x < 2**-27 */
219 return(u00 + tpi*__ieee754_log(x));
220 }
221 z = x*x;
222 u = u00+z*(u01+z*(u02+z*(u03+z*(u04+z*(u05+z*u06)))));
223 v = one+z*(v01+z*(v02+z*(v03+z*v04)));
224 return(u/v + tpi*(__ieee754_j0(x)*__ieee754_log(x)));
225}
226
227/* The asymptotic expansions of pzero is
228 * 1 - 9/128 s^2 + 11025/98304 s^4 - ..., where s = 1/x.
229 * For x >= 2, We approximate pzero by
230 * pzero(x) = 1 + (R/S)
231 * where R = pR0 + pR1*s^2 + pR2*s^4 + ... + pR5*s^10
232 * S = 1 + pS0*s^2 + ... + pS4*s^10
233 * and
234 * | pzero(x)-1-R/S | <= 2 ** ( -60.26)
235 */
236#ifdef __STDC__
237static const double pR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
238#else
239static double pR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
240#endif
241 0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
242 -7.03124999999900357484e-02, /* 0xBFB1FFFF, 0xFFFFFD32 */
243 -8.08167041275349795626e+00, /* 0xC02029D0, 0xB44FA779 */
244 -2.57063105679704847262e+02, /* 0xC0701102, 0x7B19E863 */
245 -2.48521641009428822144e+03, /* 0xC0A36A6E, 0xCD4DCAFC */
246 -5.25304380490729545272e+03, /* 0xC0B4850B, 0x36CC643D */
247};
248#ifdef __STDC__
249static const double pS8[5] = {
250#else
251static double pS8[5] = {
252#endif
253 1.16534364619668181717e+02, /* 0x405D2233, 0x07A96751 */
254 3.83374475364121826715e+03, /* 0x40ADF37D, 0x50596938 */
255 4.05978572648472545552e+04, /* 0x40E3D2BB, 0x6EB6B05F */
256 1.16752972564375915681e+05, /* 0x40FC810F, 0x8F9FA9BD */
257 4.76277284146730962675e+04, /* 0x40E74177, 0x4F2C49DC */
258};
259
260#ifdef __STDC__
261static const double pR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
262#else
263static double pR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
264#endif
265 -1.14125464691894502584e-11, /* 0xBDA918B1, 0x47E495CC */
266 -7.03124940873599280078e-02, /* 0xBFB1FFFF, 0xE69AFBC6 */
267 -4.15961064470587782438e+00, /* 0xC010A370, 0xF90C6BBF */
268 -6.76747652265167261021e+01, /* 0xC050EB2F, 0x5A7D1783 */
269 -3.31231299649172967747e+02, /* 0xC074B3B3, 0x6742CC63 */
270 -3.46433388365604912451e+02, /* 0xC075A6EF, 0x28A38BD7 */
271};
272#ifdef __STDC__
273static const double pS5[5] = {
274#else
275static double pS5[5] = {
276#endif
277 6.07539382692300335975e+01, /* 0x404E6081, 0x0C98C5DE */
278 1.05125230595704579173e+03, /* 0x40906D02, 0x5C7E2864 */
279 5.97897094333855784498e+03, /* 0x40B75AF8, 0x8FBE1D60 */
280 9.62544514357774460223e+03, /* 0x40C2CCB8, 0xFA76FA38 */
281 2.40605815922939109441e+03, /* 0x40A2CC1D, 0xC70BE864 */
282};
283
284#ifdef __STDC__
285static const double pR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
286#else
287static double pR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
288#endif
289 -2.54704601771951915620e-09, /* 0xBE25E103, 0x6FE1AA86 */
290 -7.03119616381481654654e-02, /* 0xBFB1FFF6, 0xF7C0E24B */
291 -2.40903221549529611423e+00, /* 0xC00345B2, 0xAEA48074 */
292 -2.19659774734883086467e+01, /* 0xC035F74A, 0x4CB94E14 */
293 -5.80791704701737572236e+01, /* 0xC04D0A22, 0x420A1A45 */
294 -3.14479470594888503854e+01, /* 0xC03F72AC, 0xA892D80F */
295};
296#ifdef __STDC__
297static const double pS3[5] = {
298#else
299static double pS3[5] = {
300#endif
301 3.58560338055209726349e+01, /* 0x4041ED92, 0x84077DD3 */
302 3.61513983050303863820e+02, /* 0x40769839, 0x464A7C0E */
303 1.19360783792111533330e+03, /* 0x4092A66E, 0x6D1061D6 */
304 1.12799679856907414432e+03, /* 0x40919FFC, 0xB8C39B7E */
305 1.73580930813335754692e+02, /* 0x4065B296, 0xFC379081 */
306};
307
308#ifdef __STDC__
309static const double pR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
310#else
311static double pR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
312#endif
313 -8.87534333032526411254e-08, /* 0xBE77D316, 0xE927026D */
314 -7.03030995483624743247e-02, /* 0xBFB1FF62, 0x495E1E42 */
315 -1.45073846780952986357e+00, /* 0xBFF73639, 0x8A24A843 */
316 -7.63569613823527770791e+00, /* 0xC01E8AF3, 0xEDAFA7F3 */
317 -1.11931668860356747786e+01, /* 0xC02662E6, 0xC5246303 */
318 -3.23364579351335335033e+00, /* 0xC009DE81, 0xAF8FE70F */
319};
320#ifdef __STDC__
321static const double pS2[5] = {
322#else
323static double pS2[5] = {
324#endif
325 2.22202997532088808441e+01, /* 0x40363865, 0x908B5959 */
326 1.36206794218215208048e+02, /* 0x4061069E, 0x0EE8878F */
327 2.70470278658083486789e+02, /* 0x4070E786, 0x42EA079B */
328 1.53875394208320329881e+02, /* 0x40633C03, 0x3AB6FAFF */
329 1.46576176948256193810e+01, /* 0x402D50B3, 0x44391809 */
330};
331
332#ifdef __STDC__
333 static double pzero(double x)
334#else
335 static double pzero(x)
336 double x;
337#endif
338{
339#ifdef __STDC__
340 const double *p,*q;
341#else
342 double *p,*q;
343#endif
344 double z,r,s;
345 int32_t ix;
346 p = NULL;
347 q = NULL;
348 GET_HIGH_WORD(ix,x);
349 ix &= 0x7fffffff;
350 if(ix>=0x40200000) {p = pR8; q= pS8;}
351 else if(ix>=0x40122E8B){p = pR5; q= pS5;}
352 else if(ix>=0x4006DB6D){p = pR3; q= pS3;}
353 else if(ix>=0x40000000){p = pR2; q= pS2;}
354 z = one/(x*x);
355 r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
356 s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*q[4]))));
357 return one+ r/s;
358}
359
360
361/* For x >= 8, the asymptotic expansions of qzero is
362 * -1/8 s + 75/1024 s^3 - ..., where s = 1/x.
363 * We approximate pzero by
364 * qzero(x) = s*(-1.25 + (R/S))
365 * where R = qR0 + qR1*s^2 + qR2*s^4 + ... + qR5*s^10
366 * S = 1 + qS0*s^2 + ... + qS5*s^12
367 * and
368 * | qzero(x)/s +1.25-R/S | <= 2 ** ( -61.22)
369 */
370#ifdef __STDC__
371static const double qR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
372#else
373static double qR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
374#endif
375 0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
376 7.32421874999935051953e-02, /* 0x3FB2BFFF, 0xFFFFFE2C */
377 1.17682064682252693899e+01, /* 0x40278952, 0x5BB334D6 */
378 5.57673380256401856059e+02, /* 0x40816D63, 0x15301825 */
379 8.85919720756468632317e+03, /* 0x40C14D99, 0x3E18F46D */
380 3.70146267776887834771e+04, /* 0x40E212D4, 0x0E901566 */
381};
382#ifdef __STDC__
383static const double qS8[6] = {
384#else
385static double qS8[6] = {
386#endif
387 1.63776026895689824414e+02, /* 0x406478D5, 0x365B39BC */
388 8.09834494656449805916e+03, /* 0x40BFA258, 0x4E6B0563 */
389 1.42538291419120476348e+05, /* 0x41016652, 0x54D38C3F */
390 8.03309257119514397345e+05, /* 0x412883DA, 0x83A52B43 */
391 8.40501579819060512818e+05, /* 0x4129A66B, 0x28DE0B3D */
392 -3.43899293537866615225e+05, /* 0xC114FD6D, 0x2C9530C5 */
393};
394
395#ifdef __STDC__
396static const double qR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
397#else
398static double qR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
399#endif
400 1.84085963594515531381e-11, /* 0x3DB43D8F, 0x29CC8CD9 */
401 7.32421766612684765896e-02, /* 0x3FB2BFFF, 0xD172B04C */
402 5.83563508962056953777e+00, /* 0x401757B0, 0xB9953DD3 */
403 1.35111577286449829671e+02, /* 0x4060E392, 0x0A8788E9 */
404 1.02724376596164097464e+03, /* 0x40900CF9, 0x9DC8C481 */
405 1.98997785864605384631e+03, /* 0x409F17E9, 0x53C6E3A6 */
406};
407#ifdef __STDC__
408static const double qS5[6] = {
409#else
410static double qS5[6] = {
411#endif
412 8.27766102236537761883e+01, /* 0x4054B1B3, 0xFB5E1543 */
413 2.07781416421392987104e+03, /* 0x40A03BA0, 0xDA21C0CE */
414 1.88472887785718085070e+04, /* 0x40D267D2, 0x7B591E6D */
415 5.67511122894947329769e+04, /* 0x40EBB5E3, 0x97E02372 */
416 3.59767538425114471465e+04, /* 0x40E19118, 0x1F7A54A0 */
417 -5.35434275601944773371e+03, /* 0xC0B4EA57, 0xBEDBC609 */
418};
419
420#ifdef __STDC__
421static const double qR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
422#else
423static double qR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
424#endif
425 4.37741014089738620906e-09, /* 0x3E32CD03, 0x6ADECB82 */
426 7.32411180042911447163e-02, /* 0x3FB2BFEE, 0x0E8D0842 */
427 3.34423137516170720929e+00, /* 0x400AC0FC, 0x61149CF5 */
428 4.26218440745412650017e+01, /* 0x40454F98, 0x962DAEDD */
429 1.70808091340565596283e+02, /* 0x406559DB, 0xE25EFD1F */
430 1.66733948696651168575e+02, /* 0x4064D77C, 0x81FA21E0 */
431};
432#ifdef __STDC__
433static const double qS3[6] = {
434#else
435static double qS3[6] = {
436#endif
437 4.87588729724587182091e+01, /* 0x40486122, 0xBFE343A6 */
438 7.09689221056606015736e+02, /* 0x40862D83, 0x86544EB3 */
439 3.70414822620111362994e+03, /* 0x40ACF04B, 0xE44DFC63 */
440 6.46042516752568917582e+03, /* 0x40B93C6C, 0xD7C76A28 */
441 2.51633368920368957333e+03, /* 0x40A3A8AA, 0xD94FB1C0 */
442 -1.49247451836156386662e+02, /* 0xC062A7EB, 0x201CF40F */
443};
444
445#ifdef __STDC__
446static const double qR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
447#else
448static double qR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
449#endif
450 1.50444444886983272379e-07, /* 0x3E84313B, 0x54F76BDB */
451 7.32234265963079278272e-02, /* 0x3FB2BEC5, 0x3E883E34 */
452 1.99819174093815998816e+00, /* 0x3FFFF897, 0xE727779C */
453 1.44956029347885735348e+01, /* 0x402CFDBF, 0xAAF96FE5 */
454 3.16662317504781540833e+01, /* 0x403FAA8E, 0x29FBDC4A */
455 1.62527075710929267416e+01, /* 0x403040B1, 0x71814BB4 */
456};
457#ifdef __STDC__
458static const double qS2[6] = {
459#else
460static double qS2[6] = {
461#endif
462 3.03655848355219184498e+01, /* 0x403E5D96, 0xF7C07AED */
463 2.69348118608049844624e+02, /* 0x4070D591, 0xE4D14B40 */
464 8.44783757595320139444e+02, /* 0x408A6645, 0x22B3BF22 */
465 8.82935845112488550512e+02, /* 0x408B977C, 0x9C5CC214 */
466 2.12666388511798828631e+02, /* 0x406A9553, 0x0E001365 */
467 -5.31095493882666946917e+00, /* 0xC0153E6A, 0xF8B32931 */
468};
469
470#ifdef __STDC__
471 static double qzero(double x)
472#else
473 static double qzero(x)
474 double x;
475#endif
476{
477#ifdef __STDC__
478 const double *p,*q;
479#else
480 double *p,*q;
481#endif
482 double s,r,z;
483 int32_t ix;
484 p = NULL;
485 q = NULL;
486 GET_HIGH_WORD(ix,x);
487 ix &= 0x7fffffff;
488 if(ix>=0x40200000) {p = qR8; q= qS8;}
489 else if(ix>=0x40122E8B){p = qR5; q= qS5;}
490 else if(ix>=0x4006DB6D){p = qR3; q= qS3;}
491 else if(ix>=0x40000000){p = qR2; q= qS2;}
492 z = one/(x*x);
493 r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
494 s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*(q[4]+z*q[5])))));
495 return (-.125 + r/s)/x;
496}