1 /* s_erff.c -- float version of s_erf.c. 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 3 */ 4 5 /* 6 * ==================================================== 7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 8 * 9 * Developed at SunPro, a Sun Microsystems, Inc. business. 10 * Permission to use, copy, modify, and distribute this 11 * software is freely granted, provided that this notice 12 * is preserved. 13 * ==================================================== 14 */ 15 16 #include <sys/cdefs.h> 17 #if defined(LIBM_SCCS) && !defined(lint) 18 __RCSID("$NetBSD: s_erff.c,v 1.5 1997/10/09 11:31:38 lukem Exp $"); 19 #endif 20 21 #include "math.h" 22 #include "math_private.h" 23 24 #ifdef __STDC__ 25 static const float 26 #else 27 static float 28 #endif 29 tiny = 1e-30, 30 half= 5.0000000000e-01, /* 0x3F000000 */ 31 one = 1.0000000000e+00, /* 0x3F800000 */ 32 two = 2.0000000000e+00, /* 0x40000000 */ 33 /* c = (subfloat)0.84506291151 */ 34 erx = 8.4506291151e-01, /* 0x3f58560b */ 35 /* 36 * Coefficients for approximation to erf on [0,0.84375] 37 */ 38 efx = 1.2837916613e-01, /* 0x3e0375d4 */ 39 efx8= 1.0270333290e+00, /* 0x3f8375d4 */ 40 pp0 = 1.2837916613e-01, /* 0x3e0375d4 */ 41 pp1 = -3.2504209876e-01, /* 0xbea66beb */ 42 pp2 = -2.8481749818e-02, /* 0xbce9528f */ 43 pp3 = -5.7702702470e-03, /* 0xbbbd1489 */ 44 pp4 = -2.3763017452e-05, /* 0xb7c756b1 */ 45 qq1 = 3.9791721106e-01, /* 0x3ecbbbce */ 46 qq2 = 6.5022252500e-02, /* 0x3d852a63 */ 47 qq3 = 5.0813062117e-03, /* 0x3ba68116 */ 48 qq4 = 1.3249473704e-04, /* 0x390aee49 */ 49 qq5 = -3.9602282413e-06, /* 0xb684e21a */ 50 /* 51 * Coefficients for approximation to erf in [0.84375,1.25] 52 */ 53 pa0 = -2.3621185683e-03, /* 0xbb1acdc6 */ 54 pa1 = 4.1485610604e-01, /* 0x3ed46805 */ 55 pa2 = -3.7220788002e-01, /* 0xbebe9208 */ 56 pa3 = 3.1834661961e-01, /* 0x3ea2fe54 */ 57 pa4 = -1.1089469492e-01, /* 0xbde31cc2 */ 58 pa5 = 3.5478305072e-02, /* 0x3d1151b3 */ 59 pa6 = -2.1663755178e-03, /* 0xbb0df9c0 */ 60 qa1 = 1.0642088205e-01, /* 0x3dd9f331 */ 61 qa2 = 5.4039794207e-01, /* 0x3f0a5785 */ 62 qa3 = 7.1828655899e-02, /* 0x3d931ae7 */ 63 qa4 = 1.2617121637e-01, /* 0x3e013307 */ 64 qa5 = 1.3637083583e-02, /* 0x3c5f6e13 */ 65 qa6 = 1.1984500103e-02, /* 0x3c445aa3 */ 66 /* 67 * Coefficients for approximation to erfc in [1.25,1/0.35] 68 */ 69 ra0 = -9.8649440333e-03, /* 0xbc21a093 */ 70 ra1 = -6.9385856390e-01, /* 0xbf31a0b7 */ 71 ra2 = -1.0558626175e+01, /* 0xc128f022 */ 72 ra3 = -6.2375331879e+01, /* 0xc2798057 */ 73 ra4 = -1.6239666748e+02, /* 0xc322658c */ 74 ra5 = -1.8460508728e+02, /* 0xc3389ae7 */ 75 ra6 = -8.1287437439e+01, /* 0xc2a2932b */ 76 ra7 = -9.8143291473e+00, /* 0xc11d077e */ 77 sa1 = 1.9651271820e+01, /* 0x419d35ce */ 78 sa2 = 1.3765776062e+02, /* 0x4309a863 */ 79 sa3 = 4.3456588745e+02, /* 0x43d9486f */ 80 sa4 = 6.4538726807e+02, /* 0x442158c9 */ 81 sa5 = 4.2900814819e+02, /* 0x43d6810b */ 82 sa6 = 1.0863500214e+02, /* 0x42d9451f */ 83 sa7 = 6.5702495575e+00, /* 0x40d23f7c */ 84 sa8 = -6.0424413532e-02, /* 0xbd777f97 */ 85 /* 86 * Coefficients for approximation to erfc in [1/.35,28] 87 */ 88 rb0 = -9.8649431020e-03, /* 0xbc21a092 */ 89 rb1 = -7.9928326607e-01, /* 0xbf4c9dd4 */ 90 rb2 = -1.7757955551e+01, /* 0xc18e104b */ 91 rb3 = -1.6063638306e+02, /* 0xc320a2ea */ 92 rb4 = -6.3756646729e+02, /* 0xc41f6441 */ 93 rb5 = -1.0250950928e+03, /* 0xc480230b */ 94 rb6 = -4.8351919556e+02, /* 0xc3f1c275 */ 95 sb1 = 3.0338060379e+01, /* 0x41f2b459 */ 96 sb2 = 3.2579251099e+02, /* 0x43a2e571 */ 97 sb3 = 1.5367296143e+03, /* 0x44c01759 */ 98 sb4 = 3.1998581543e+03, /* 0x4547fdbb */ 99 sb5 = 2.5530502930e+03, /* 0x451f90ce */ 100 sb6 = 4.7452853394e+02, /* 0x43ed43a7 */ 101 sb7 = -2.2440952301e+01; /* 0xc1b38712 */ 102 103 #ifdef __STDC__ 104 float erff(float x) 105 #else 106 float erff(x) 107 float x; 108 #endif 109 { 110 int32_t hx,ix,i; 111 float R,S,P,Q,s,y,z,r; 112 GET_FLOAT_WORD(hx,x); 113 ix = hx&0x7fffffff; 114 if(ix>=0x7f800000) { /* erf(nan)=nan */ 115 i = ((u_int32_t)hx>>31)<<1; 116 return (float)(1-i)+one/x; /* erf(+-inf)=+-1 */ 117 } 118 119 if(ix < 0x3f580000) { /* |x|<0.84375 */ 120 if(ix < 0x31800000) { /* |x|<2**-28 */ 121 if (ix < 0x04000000) 122 /*avoid underflow */ 123 return (float)0.125*((float)8.0*x+efx8*x); 124 return x + efx*x; 125 } 126 z = x*x; 127 r = pp0+z*(pp1+z*(pp2+z*(pp3+z*pp4))); 128 s = one+z*(qq1+z*(qq2+z*(qq3+z*(qq4+z*qq5)))); 129 y = r/s; 130 return x + x*y; 131 } 132 if(ix < 0x3fa00000) { /* 0.84375 <= |x| < 1.25 */ 133 s = fabsf(x)-one; 134 P = pa0+s*(pa1+s*(pa2+s*(pa3+s*(pa4+s*(pa5+s*pa6))))); 135 Q = one+s*(qa1+s*(qa2+s*(qa3+s*(qa4+s*(qa5+s*qa6))))); 136 if(hx>=0) return erx + P/Q; else return -erx - P/Q; 137 } 138 if (ix >= 0x40c00000) { /* inf>|x|>=6 */ 139 if(hx>=0) return one-tiny; else return tiny-one; 140 } 141 x = fabsf(x); 142 s = one/(x*x); 143 if(ix< 0x4036DB6E) { /* |x| < 1/0.35 */ 144 R=ra0+s*(ra1+s*(ra2+s*(ra3+s*(ra4+s*( 145 ra5+s*(ra6+s*ra7)))))); 146 S=one+s*(sa1+s*(sa2+s*(sa3+s*(sa4+s*( 147 sa5+s*(sa6+s*(sa7+s*sa8))))))); 148 } else { /* |x| >= 1/0.35 */ 149 R=rb0+s*(rb1+s*(rb2+s*(rb3+s*(rb4+s*( 150 rb5+s*rb6))))); 151 S=one+s*(sb1+s*(sb2+s*(sb3+s*(sb4+s*( 152 sb5+s*(sb6+s*sb7)))))); 153 } 154 GET_FLOAT_WORD(ix,x); 155 SET_FLOAT_WORD(z,ix&0xfffff000); 156 r = __ieee754_expf(-z*z-(float)0.5625)*__ieee754_expf((z-x)*(z+x)+R/S); 157 if(hx>=0) return one-r/x; else return r/x-one; 158 } 159 160 #ifdef __STDC__ 161 float erfcf(float x) 162 #else 163 float erfcf(x) 164 float x; 165 #endif 166 { 167 int32_t hx,ix; 168 float R,S,P,Q,s,y,z,r; 169 GET_FLOAT_WORD(hx,x); 170 ix = hx&0x7fffffff; 171 if(ix>=0x7f800000) { /* erfc(nan)=nan */ 172 /* erfc(+-inf)=0,2 */ 173 return (float)(((u_int32_t)hx>>31)<<1)+one/x; 174 } 175 176 if(ix < 0x3f580000) { /* |x|<0.84375 */ 177 if(ix < 0x23800000) /* |x|<2**-56 */ 178 return one-x; 179 z = x*x; 180 r = pp0+z*(pp1+z*(pp2+z*(pp3+z*pp4))); 181 s = one+z*(qq1+z*(qq2+z*(qq3+z*(qq4+z*qq5)))); 182 y = r/s; 183 if(hx < 0x3e800000) { /* x<1/4 */ 184 return one-(x+x*y); 185 } else { 186 r = x*y; 187 r += (x-half); 188 return half - r ; 189 } 190 } 191 if(ix < 0x3fa00000) { /* 0.84375 <= |x| < 1.25 */ 192 s = fabsf(x)-one; 193 P = pa0+s*(pa1+s*(pa2+s*(pa3+s*(pa4+s*(pa5+s*pa6))))); 194 Q = one+s*(qa1+s*(qa2+s*(qa3+s*(qa4+s*(qa5+s*qa6))))); 195 if(hx>=0) { 196 z = one-erx; return z - P/Q; 197 } else { 198 z = erx+P/Q; return one+z; 199 } 200 } 201 if (ix < 0x41e00000) { /* |x|<28 */ 202 x = fabsf(x); 203 s = one/(x*x); 204 if(ix< 0x4036DB6D) { /* |x| < 1/.35 ~ 2.857143*/ 205 R=ra0+s*(ra1+s*(ra2+s*(ra3+s*(ra4+s*( 206 ra5+s*(ra6+s*ra7)))))); 207 S=one+s*(sa1+s*(sa2+s*(sa3+s*(sa4+s*( 208 sa5+s*(sa6+s*(sa7+s*sa8))))))); 209 } else { /* |x| >= 1/.35 ~ 2.857143 */ 210 if(hx<0&&ix>=0x40c00000) return two-tiny;/* x < -6 */ 211 R=rb0+s*(rb1+s*(rb2+s*(rb3+s*(rb4+s*( 212 rb5+s*rb6))))); 213 S=one+s*(sb1+s*(sb2+s*(sb3+s*(sb4+s*( 214 sb5+s*(sb6+s*sb7)))))); 215 } 216 GET_FLOAT_WORD(ix,x); 217 SET_FLOAT_WORD(z,ix&0xfffff000); 218 r = __ieee754_expf(-z*z-(float)0.5625)* 219 __ieee754_expf((z-x)*(z+x)+R/S); 220 if(hx>0) return r/x; else return two-r/x; 221 } else { 222 if(hx>0) return tiny*tiny; else return two-tiny; 223 } 224 } 225