sysdeps/ieee754/dbl-64/e_j0.c

   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 /* Modified by Naohiko Shimizu/Tokai University, Japan 1997/08/26,
  13    for performance improvement on pipelined processors.
  14 */
  15
  16 /* __ieee754_j0(x), __ieee754_y0(x)
  17  * Bessel function of the first and second kinds of order zero.
  18  * Method -- j0(x):
  19  *      1. For tiny x, we use j0(x) = 1 - x^2/4 + x^4/64 - ...
  20  *      2. Reduce x to |x| since j0(x)=j0(-x),  and
  21  *         for x in (0,2)
  22  *              j0(x) = 1-z/4+ z^2*R0/S0,  where z = x*x;
  23  *         (precision:  |j0-1+z/4-z^2R0/S0 |<2**-63.67 )
  24  *         for x in (2,inf)
  25  *              j0(x) = sqrt(2/(pi*x))*(p0(x)*cos(x0)-q0(x)*sin(x0))
  26  *         where x0 = x-pi/4. It is better to compute sin(x0),cos(x0)
  27  *         as follow:
  28  *              cos(x0) = cos(x)cos(pi/4)+sin(x)sin(pi/4)
  29  *                      = 1/sqrt(2) * (cos(x) + sin(x))
  30  *              sin(x0) = sin(x)cos(pi/4)-cos(x)sin(pi/4)
  31  *                      = 1/sqrt(2) * (sin(x) - cos(x))
  32  *         (To avoid cancellation, use
  33  *              sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
  34  *          to compute the worse one.)
  35  *
  36  *      3 Special cases
  37  *              j0(nan)= nan
  38  *              j0(0) = 1
  39  *              j0(inf) = 0
  40  *
  41  * Method -- y0(x):
  42  *      1. For x<2.
  43  *         Since
  44  *              y0(x) = 2/pi*(j0(x)*(ln(x/2)+Euler) + x^2/4 - ...)
  45  *         therefore y0(x)-2/pi*j0(x)*ln(x) is an even function.
  46  *         We use the following function to approximate y0,
  47  *              y0(x) = U(z)/V(z) + (2/pi)*(j0(x)*ln(x)), z= x^2
  48  *         where
  49  *              U(z) = u00 + u01*z + ... + u06*z^6
  50  *              V(z) = 1  + v01*z + ... + v04*z^4
  51  *         with absolute approximation error bounded by 2**-72.
  52  *         Note: For tiny x, U/V = u0 and j0(x)~1, hence
  53  *              y0(tiny) = u0 + (2/pi)*ln(tiny), (choose tiny<2**-27)
  54  *      2. For x>=2.
  55  *              y0(x) = sqrt(2/(pi*x))*(p0(x)*cos(x0)+q0(x)*sin(x0))
  56  *         where x0 = x-pi/4. It is better to compute sin(x0),cos(x0)
  57  *         by the method mentioned above.
  58  *      3. Special cases: y0(0)=-inf, y0(x<0)=NaN, y0(inf)=0.
  59  */
  60
  61 #include <math.h>
  62 #include <math_private.h>
  63
  64 static double pzero(double), qzero(double);
  65
  66 static const double
  67 huge    = 1e300,
  68 one     = 1.0,
  69 invsqrtpi=  5.64189583547756279280e-01, /* 0x3FE20DD7, 0x50429B6D */
  70 tpi      =  6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
  71                 /* R0/S0 on [0, 2.00] */
  72 R[]  =  {0.0, 0.0, 1.56249999999999947958e-02, /* 0x3F8FFFFF, 0xFFFFFFFD */
  73  -1.89979294238854721751e-04, /* 0xBF28E6A5, 0xB61AC6E9 */
  74   1.82954049532700665670e-06, /* 0x3EBEB1D1, 0x0C503919 */
  75  -4.61832688532103189199e-09}, /* 0xBE33D5E7, 0x73D63FCE */
  76 S[]  =  {0.0, 1.56191029464890010492e-02, /* 0x3F8FFCE8, 0x82C8C2A4 */
  77   1.16926784663337450260e-04, /* 0x3F1EA6D2, 0xDD57DBF4 */
  78   5.13546550207318111446e-07, /* 0x3EA13B54, 0xCE84D5A9 */
  79   1.16614003333790000205e-09}; /* 0x3E1408BC, 0xF4745D8F */
  80
  81 static const double zero = 0.0;
  82
  83 double
  84 __ieee754_j0(double x)
  85 {
  86         double z, s,c,ss,cc,r,u,v,r1,r2,s1,s2,z2,z4;
  87         int32_t hx,ix;
  88
  89         GET_HIGH_WORD(hx,x);
  90         ix = hx&0x7fffffff;
  91         if(ix>=0x7ff00000) return one/(x*x);
  92         x = fabs(x);
  93         if(ix >= 0x40000000) {  /* |x| >= 2.0 */
  94                 __sincos (x, &s, &c);
  95                 ss = s-c;
  96                 cc = s+c;
  97                 if(ix<0x7fe00000) {  /* make sure x+x not overflow */
  98                     z = -__cos(x+x);
  99                     if ((s*c)<zero) cc = z/ss;
 100                     else            ss = z/cc;
 101                 }
 102         /*
 103          * j0(x) = 1/sqrt(pi) * (P(0,x)*cc - Q(0,x)*ss) / sqrt(x)
 104          * y0(x) = 1/sqrt(pi) * (P(0,x)*ss + Q(0,x)*cc) / sqrt(x)
 105          */
 106                 if(ix>0x48000000) z = (invsqrtpi*cc)/__ieee754_sqrt(x);
 107                 else {
 108                     u = pzero(x); v = qzero(x);
 109                     z = invsqrtpi*(u*cc-v*ss)/__ieee754_sqrt(x);
 110                 }
 111                 return z;
 112         }
 113         if(ix<0x3f200000) {     /* |x| < 2**-13 */
 114           math_force_eval(huge+x);      /* raise inexact if x != 0 */
 115           if(ix<0x3e400000) return one; /* |x|<2**-27 */
 116           else        return one - 0.25*x*x;
 117         }
 118         z = x*x;
 119 #ifdef DO_NOT_USE_THIS
 120         r =  z*(R02+z*(R03+z*(R04+z*R05)));
 121         s =  one+z*(S01+z*(S02+z*(S03+z*S04)));
 122 #else
 123         r1 = z*R[2]; z2=z*z;
 124         r2 = R[3]+z*R[4]; z4=z2*z2;
 125         r  = r1 + z2*r2 + z4*R[5];
 126         s1 = one+z*S[1];
 127         s2 = S[2]+z*S[3];
 128         s = s1 + z2*s2 + z4*S[4];
 129 #endif
 130         if(ix < 0x3FF00000) {   /* |x| < 1.00 */
 131             return one + z*(-0.25+(r/s));
 132         } else {
 133             u = 0.5*x;
 134             return((one+u)*(one-u)+z*(r/s));
 135         }
 136 }
 137 strong_alias (__ieee754_j0, __j0_finite)
 138
 139 static const double
 140 U[]  = {-7.38042951086872317523e-02, /* 0xBFB2E4D6, 0x99CBD01F */
 141   1.76666452509181115538e-01, /* 0x3FC69D01, 0x9DE9E3FC */
 142  -1.38185671945596898896e-02, /* 0xBF8C4CE8, 0xB16CFA97 */
 143   3.47453432093683650238e-04, /* 0x3F36C54D, 0x20B29B6B */
 144  -3.81407053724364161125e-06, /* 0xBECFFEA7, 0x73D25CAD */
 145   1.95590137035022920206e-08, /* 0x3E550057, 0x3B4EABD4 */
 146  -3.98205194132103398453e-11}, /* 0xBDC5E43D, 0x693FB3C8 */
 147 V[]  =  {1.27304834834123699328e-02, /* 0x3F8A1270, 0x91C9C71A */
 148   7.60068627350353253702e-05, /* 0x3F13ECBB, 0xF578C6C1 */
 149   2.59150851840457805467e-07, /* 0x3E91642D, 0x7FF202FD */
 150   4.41110311332675467403e-10}; /* 0x3DFE5018, 0x3BD6D9EF */
 151
 152 double
 153 __ieee754_y0(double x)
 154 {
 155         double z, s,c,ss,cc,u,v,z2,z4,z6,u1,u2,u3,v1,v2;
 156         int32_t hx,ix,lx;
 157
 158         EXTRACT_WORDS(hx,lx,x);
 159         ix = 0x7fffffff&hx;
 160     /* Y0(NaN) is NaN, y0(-inf) is Nan, y0(inf) is 0, y0(0) is -inf.  */
 161         if(ix>=0x7ff00000) return  one/(x+x*x);
 162         if((ix|lx)==0) return -HUGE_VAL+x; /* -inf and overflow exception.  */
 163         if(hx<0) return zero/(zero*x);
 164         if(ix >= 0x40000000) {  /* |x| >= 2.0 */
 165         /* y0(x) = sqrt(2/(pi*x))*(p0(x)*sin(x0)+q0(x)*cos(x0))
 166          * where x0 = x-pi/4
 167          *      Better formula:
 168          *              cos(x0) = cos(x)cos(pi/4)+sin(x)sin(pi/4)
 169          *                      =  1/sqrt(2) * (sin(x) + cos(x))
 170          *              sin(x0) = sin(x)cos(3pi/4)-cos(x)sin(3pi/4)
 171          *                      =  1/sqrt(2) * (sin(x) - cos(x))
 172          * To avoid cancellation, use
 173          *              sin(x) +- cos(x) = -cos(2x)/(sin(x) -+ cos(x))
 174          * to compute the worse one.
 175          */
 176                 __sincos (x, &s, &c);
 177                 ss = s-c;
 178                 cc = s+c;
 179         /*
 180          * j0(x) = 1/sqrt(pi) * (P(0,x)*cc - Q(0,x)*ss) / sqrt(x)
 181          * y0(x) = 1/sqrt(pi) * (P(0,x)*ss + Q(0,x)*cc) / sqrt(x)
 182          */
 183                 if(ix<0x7fe00000) {  /* make sure x+x not overflow */
 184                     z = -__cos(x+x);
 185                     if ((s*c)<zero) cc = z/ss;
 186                     else            ss = z/cc;
 187                 }
 188                 if(ix>0x48000000) z = (invsqrtpi*ss)/__ieee754_sqrt(x);
 189                 else {
 190                     u = pzero(x); v = qzero(x);
 191                     z = invsqrtpi*(u*ss+v*cc)/__ieee754_sqrt(x);
 192                 }
 193                 return z;
 194         }
 195         if(ix<=0x3e400000) {    /* x < 2**-27 */
 196             return(U[0] + tpi*__ieee754_log(x));
 197         }
 198         z = x*x;
 199 #ifdef DO_NOT_USE_THIS
 200         u = u00+z*(u01+z*(u02+z*(u03+z*(u04+z*(u05+z*u06)))));
 201         v = one+z*(v01+z*(v02+z*(v03+z*v04)));
 202 #else
 203         u1 = U[0]+z*U[1]; z2=z*z;
 204         u2 = U[2]+z*U[3]; z4=z2*z2;
 205         u3 = U[4]+z*U[5]; z6=z4*z2;
 206         u = u1 + z2*u2 + z4*u3 + z6*U[6];
 207         v1 = one+z*V[0];
 208         v2 = V[1]+z*V[2];
 209         v = v1 + z2*v2 + z4*V[3];
 210 #endif
 211         return(u/v + tpi*(__ieee754_j0(x)*__ieee754_log(x)));
 212 }
 213 strong_alias (__ieee754_y0, __y0_finite)
 214
 215 /* The asymptotic expansions of pzero is
 216  *      1 - 9/128 s^2 + 11025/98304 s^4 - ...,  where s = 1/x.
 217  * For x >= 2, We approximate pzero by
 218  *      pzero(x) = 1 + (R/S)
 219  * where  R = pR0 + pR1*s^2 + pR2*s^4 + ... + pR5*s^10
 220  *        S = 1 + pS0*s^2 + ... + pS4*s^10
 221  * and
 222  *      | pzero(x)-1-R/S | <= 2  ** ( -60.26)
 223  */
 224 static const double pR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
 225   0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
 226  -7.03124999999900357484e-02, /* 0xBFB1FFFF, 0xFFFFFD32 */
 227  -8.08167041275349795626e+00, /* 0xC02029D0, 0xB44FA779 */
 228  -2.57063105679704847262e+02, /* 0xC0701102, 0x7B19E863 */
 229  -2.48521641009428822144e+03, /* 0xC0A36A6E, 0xCD4DCAFC */
 230  -5.25304380490729545272e+03, /* 0xC0B4850B, 0x36CC643D */
 231 };
 232 static const double pS8[5] = {
 233   1.16534364619668181717e+02, /* 0x405D2233, 0x07A96751 */
 234   3.83374475364121826715e+03, /* 0x40ADF37D, 0x50596938 */
 235   4.05978572648472545552e+04, /* 0x40E3D2BB, 0x6EB6B05F */
 236   1.16752972564375915681e+05, /* 0x40FC810F, 0x8F9FA9BD */
 237   4.76277284146730962675e+04, /* 0x40E74177, 0x4F2C49DC */
 238 };
 239
 240 static const double pR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
 241  -1.14125464691894502584e-11, /* 0xBDA918B1, 0x47E495CC */
 242  -7.03124940873599280078e-02, /* 0xBFB1FFFF, 0xE69AFBC6 */
 243  -4.15961064470587782438e+00, /* 0xC010A370, 0xF90C6BBF */
 244  -6.76747652265167261021e+01, /* 0xC050EB2F, 0x5A7D1783 */
 245  -3.31231299649172967747e+02, /* 0xC074B3B3, 0x6742CC63 */
 246  -3.46433388365604912451e+02, /* 0xC075A6EF, 0x28A38BD7 */
 247 };
 248 static const double pS5[5] = {
 249   6.07539382692300335975e+01, /* 0x404E6081, 0x0C98C5DE */
 250   1.05125230595704579173e+03, /* 0x40906D02, 0x5C7E2864 */
 251   5.97897094333855784498e+03, /* 0x40B75AF8, 0x8FBE1D60 */
 252   9.62544514357774460223e+03, /* 0x40C2CCB8, 0xFA76FA38 */
 253   2.40605815922939109441e+03, /* 0x40A2CC1D, 0xC70BE864 */
 254 };
 255
 256 static const double pR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
 257  -2.54704601771951915620e-09, /* 0xBE25E103, 0x6FE1AA86 */
 258  -7.03119616381481654654e-02, /* 0xBFB1FFF6, 0xF7C0E24B */
 259  -2.40903221549529611423e+00, /* 0xC00345B2, 0xAEA48074 */
 260  -2.19659774734883086467e+01, /* 0xC035F74A, 0x4CB94E14 */
 261  -5.80791704701737572236e+01, /* 0xC04D0A22, 0x420A1A45 */
 262  -3.14479470594888503854e+01, /* 0xC03F72AC, 0xA892D80F */
 263 };
 264 static const double pS3[5] = {
 265   3.58560338055209726349e+01, /* 0x4041ED92, 0x84077DD3 */
 266   3.61513983050303863820e+02, /* 0x40769839, 0x464A7C0E */
 267   1.19360783792111533330e+03, /* 0x4092A66E, 0x6D1061D6 */
 268   1.12799679856907414432e+03, /* 0x40919FFC, 0xB8C39B7E */
 269   1.73580930813335754692e+02, /* 0x4065B296, 0xFC379081 */
 270 };
 271
 272 static const double pR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
 273  -8.87534333032526411254e-08, /* 0xBE77D316, 0xE927026D */
 274  -7.03030995483624743247e-02, /* 0xBFB1FF62, 0x495E1E42 */
 275  -1.45073846780952986357e+00, /* 0xBFF73639, 0x8A24A843 */
 276  -7.63569613823527770791e+00, /* 0xC01E8AF3, 0xEDAFA7F3 */
 277  -1.11931668860356747786e+01, /* 0xC02662E6, 0xC5246303 */
 278  -3.23364579351335335033e+00, /* 0xC009DE81, 0xAF8FE70F */
 279 };
 280 static const double pS2[5] = {
 281   2.22202997532088808441e+01, /* 0x40363865, 0x908B5959 */
 282   1.36206794218215208048e+02, /* 0x4061069E, 0x0EE8878F */
 283   2.70470278658083486789e+02, /* 0x4070E786, 0x42EA079B */
 284   1.53875394208320329881e+02, /* 0x40633C03, 0x3AB6FAFF */
 285   1.46576176948256193810e+01, /* 0x402D50B3, 0x44391809 */
 286 };
 287
 288 static double
 289 pzero(double x)
 290 {
 291         const double *p,*q;
 292         double z,r,s,z2,z4,r1,r2,r3,s1,s2,s3;
 293         int32_t ix;
 294         GET_HIGH_WORD(ix,x);
 295         ix &= 0x7fffffff;
 296         if(ix>=0x40200000)     {p = pR8; q= pS8;}
 297         else if(ix>=0x40122E8B){p = pR5; q= pS5;}
 298         else if(ix>=0x4006DB6D){p = pR3; q= pS3;}
 299         else if(ix>=0x40000000){p = pR2; q= pS2;}
 300         z = one/(x*x);
 301 #ifdef DO_NOT_USE_THIS
 302         r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
 303         s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*q[4]))));
 304 #else
 305         r1 = p[0]+z*p[1]; z2=z*z;
 306         r2 = p[2]+z*p[3]; z4=z2*z2;
 307         r3 = p[4]+z*p[5];
 308         r = r1 + z2*r2 + z4*r3;
 309         s1 = one+z*q[0];
 310         s2 = q[1]+z*q[2];
 311         s3 = q[3]+z*q[4];
 312         s = s1 + z2*s2 + z4*s3;
 313 #endif
 314         return one+ r/s;
 315 }
 316
 317
 318 /* For x >= 8, the asymptotic expansions of qzero is
 319  *      -1/8 s + 75/1024 s^3 - ..., where s = 1/x.
 320  * We approximate pzero by
 321  *      qzero(x) = s*(-1.25 + (R/S))
 322  * where  R = qR0 + qR1*s^2 + qR2*s^4 + ... + qR5*s^10
 323  *        S = 1 + qS0*s^2 + ... + qS5*s^12
 324  * and
 325  *      | qzero(x)/s +1.25-R/S | <= 2  ** ( -61.22)
 326  */
 327 static const double qR8[6] = { /* for x in [inf, 8]=1/[0,0.125] */
 328   0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
 329   7.32421874999935051953e-02, /* 0x3FB2BFFF, 0xFFFFFE2C */
 330   1.17682064682252693899e+01, /* 0x40278952, 0x5BB334D6 */
 331   5.57673380256401856059e+02, /* 0x40816D63, 0x15301825 */
 332   8.85919720756468632317e+03, /* 0x40C14D99, 0x3E18F46D */
 333   3.70146267776887834771e+04, /* 0x40E212D4, 0x0E901566 */
 334 };
 335 static const double qS8[6] = {
 336   1.63776026895689824414e+02, /* 0x406478D5, 0x365B39BC */
 337   8.09834494656449805916e+03, /* 0x40BFA258, 0x4E6B0563 */
 338   1.42538291419120476348e+05, /* 0x41016652, 0x54D38C3F */
 339   8.03309257119514397345e+05, /* 0x412883DA, 0x83A52B43 */
 340   8.40501579819060512818e+05, /* 0x4129A66B, 0x28DE0B3D */
 341  -3.43899293537866615225e+05, /* 0xC114FD6D, 0x2C9530C5 */
 342 };
 343
 344 static const double qR5[6] = { /* for x in [8,4.5454]=1/[0.125,0.22001] */
 345   1.84085963594515531381e-11, /* 0x3DB43D8F, 0x29CC8CD9 */
 346   7.32421766612684765896e-02, /* 0x3FB2BFFF, 0xD172B04C */
 347   5.83563508962056953777e+00, /* 0x401757B0, 0xB9953DD3 */
 348   1.35111577286449829671e+02, /* 0x4060E392, 0x0A8788E9 */
 349   1.02724376596164097464e+03, /* 0x40900CF9, 0x9DC8C481 */
 350   1.98997785864605384631e+03, /* 0x409F17E9, 0x53C6E3A6 */
 351 };
 352 static const double qS5[6] = {
 353   8.27766102236537761883e+01, /* 0x4054B1B3, 0xFB5E1543 */
 354   2.07781416421392987104e+03, /* 0x40A03BA0, 0xDA21C0CE */
 355   1.88472887785718085070e+04, /* 0x40D267D2, 0x7B591E6D */
 356   5.67511122894947329769e+04, /* 0x40EBB5E3, 0x97E02372 */
 357   3.59767538425114471465e+04, /* 0x40E19118, 0x1F7A54A0 */
 358  -5.35434275601944773371e+03, /* 0xC0B4EA57, 0xBEDBC609 */
 359 };
 360
 361 static const double qR3[6] = {/* for x in [4.547,2.8571]=1/[0.2199,0.35001] */
 362   4.37741014089738620906e-09, /* 0x3E32CD03, 0x6ADECB82 */
 363   7.32411180042911447163e-02, /* 0x3FB2BFEE, 0x0E8D0842 */
 364   3.34423137516170720929e+00, /* 0x400AC0FC, 0x61149CF5 */
 365   4.26218440745412650017e+01, /* 0x40454F98, 0x962DAEDD */
 366   1.70808091340565596283e+02, /* 0x406559DB, 0xE25EFD1F */
 367   1.66733948696651168575e+02, /* 0x4064D77C, 0x81FA21E0 */
 368 };
 369 static const double qS3[6] = {
 370   4.87588729724587182091e+01, /* 0x40486122, 0xBFE343A6 */
 371   7.09689221056606015736e+02, /* 0x40862D83, 0x86544EB3 */
 372   3.70414822620111362994e+03, /* 0x40ACF04B, 0xE44DFC63 */
 373   6.46042516752568917582e+03, /* 0x40B93C6C, 0xD7C76A28 */
 374   2.51633368920368957333e+03, /* 0x40A3A8AA, 0xD94FB1C0 */
 375  -1.49247451836156386662e+02, /* 0xC062A7EB, 0x201CF40F */
 376 };
 377
 378 static const double qR2[6] = {/* for x in [2.8570,2]=1/[0.3499,0.5] */
 379   1.50444444886983272379e-07, /* 0x3E84313B, 0x54F76BDB */
 380   7.32234265963079278272e-02, /* 0x3FB2BEC5, 0x3E883E34 */
 381   1.99819174093815998816e+00, /* 0x3FFFF897, 0xE727779C */
 382   1.44956029347885735348e+01, /* 0x402CFDBF, 0xAAF96FE5 */
 383   3.16662317504781540833e+01, /* 0x403FAA8E, 0x29FBDC4A */
 384   1.62527075710929267416e+01, /* 0x403040B1, 0x71814BB4 */
 385 };
 386 static const double qS2[6] = {
 387   3.03655848355219184498e+01, /* 0x403E5D96, 0xF7C07AED */
 388   2.69348118608049844624e+02, /* 0x4070D591, 0xE4D14B40 */
 389   8.44783757595320139444e+02, /* 0x408A6645, 0x22B3BF22 */
 390   8.82935845112488550512e+02, /* 0x408B977C, 0x9C5CC214 */
 391   2.12666388511798828631e+02, /* 0x406A9553, 0x0E001365 */
 392  -5.31095493882666946917e+00, /* 0xC0153E6A, 0xF8B32931 */
 393 };
 394
 395 static double
 396 qzero(double x)
 397 {
 398         const double *p,*q;
 399         double s,r,z,z2,z4,z6,r1,r2,r3,s1,s2,s3;
 400         int32_t ix;
 401         GET_HIGH_WORD(ix,x);
 402         ix &= 0x7fffffff;
 403         if(ix>=0x40200000)     {p = qR8; q= qS8;}
 404         else if(ix>=0x40122E8B){p = qR5; q= qS5;}
 405         else if(ix>=0x4006DB6D){p = qR3; q= qS3;}
 406         else if(ix>=0x40000000){p = qR2; q= qS2;}
 407         z = one/(x*x);
 408 #ifdef DO_NOT_USE_THIS
 409         r = p[0]+z*(p[1]+z*(p[2]+z*(p[3]+z*(p[4]+z*p[5]))));
 410         s = one+z*(q[0]+z*(q[1]+z*(q[2]+z*(q[3]+z*(q[4]+z*q[5])))));
 411 #else
 412         r1 = p[0]+z*p[1]; z2=z*z;
 413         r2 = p[2]+z*p[3]; z4=z2*z2;
 414         r3 = p[4]+z*p[5]; z6=z4*z2;
 415         r= r1 + z2*r2 + z4*r3;
 416         s1 = one+z*q[0];
 417         s2 = q[1]+z*q[2];
 418         s3 = q[3]+z*q[4];
 419         s = s1 + z2*s2 + z4*s3 +z6*q[5];
 420 #endif
 421         return (-.125 + r/s)/x;
 422 }