1 2 /* 3 * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 /* __ieee754_asin(x) 28 * Method : 29 * Since asin(x) = x + x^3/6 + x^5*3/40 + x^7*15/336 + ... 30 * we approximate asin(x) on [0,0.5] by 31 * asin(x) = x + x*x^2*R(x^2) 32 * where 33 * R(x^2) is a rational approximation of (asin(x)-x)/x^3 34 * and its remez error is bounded by 35 * |(asin(x)-x)/x^3 - R(x^2)| < 2^(-58.75) 36 * 37 * For x in [0.5,1] 38 * asin(x) = pi/2-2*asin(sqrt((1-x)/2)) 39 * Let y = (1-x), z = y/2, s := sqrt(z), and pio2_hi+pio2_lo=pi/2; 40 * then for x>0.98 41 * asin(x) = pi/2 - 2*(s+s*z*R(z)) 42 * = pio2_hi - (2*(s+s*z*R(z)) - pio2_lo) 43 * For x<=0.98, let pio4_hi = pio2_hi/2, then 44 * f = hi part of s; 45 * c = sqrt(z) - f = (z-f*f)/(s+f) ...f+c=sqrt(z) 46 * and 47 * asin(x) = pi/2 - 2*(s+s*z*R(z)) 48 * = pio4_hi+(pio4-2s)-(2s*z*R(z)-pio2_lo) 49 * = pio4_hi+(pio4-2f)-(2s*z*R(z)-(pio2_lo+2c)) 50 * 51 * Special cases: 52 * if x is NaN, return x itself; 53 * if |x|>1, return NaN with invalid signal. 54 * 55 */ 56 57 58 #include "fdlibm.h" 59 60 #ifdef __STDC__ 61 static const double 62 #else 63 static double 64 #endif 65 one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */ 66 huge = 1.000e+300, 67 pio2_hi = 1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */ 68 pio2_lo = 6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */ 69 pio4_hi = 7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */ 70 /* coefficient for R(x^2) */ 71 pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */ 72 pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */ 73 pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */ 74 pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */ 75 pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */ 76 pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */ 77 qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */ 78 qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */ 79 qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */ 80 qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */ 81 82 #ifdef __STDC__ 83 double __ieee754_asin(double x) 84 #else 85 double __ieee754_asin(x) 86 double x; 87 #endif 88 { 89 double t=0,w,p,q,c,r,s; 90 int hx,ix; 91 hx = __HI(x); 92 ix = hx&0x7fffffff; 93 if(ix>= 0x3ff00000) { /* |x|>= 1 */ 94 if(((ix-0x3ff00000)|__LO(x))==0) 95 /* asin(1)=+-pi/2 with inexact */ 96 return x*pio2_hi+x*pio2_lo; 97 return (x-x)/(x-x); /* asin(|x|>1) is NaN */ 98 } else if (ix<0x3fe00000) { /* |x|<0.5 */ 99 if(ix<0x3e400000) { /* if |x| < 2**-27 */ 100 if(huge+x>one) return x;/* return x with inexact if x!=0*/ 101 } else 102 t = x*x; 103 p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5))))); 104 q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4))); 105 w = p/q; 106 return x+x*w; 107 } 108 /* 1> |x|>= 0.5 */ 109 w = one-fabs(x); 110 t = w*0.5; 111 p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5))))); 112 q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4))); 113 s = sqrt(t); 114 if(ix>=0x3FEF3333) { /* if |x| > 0.975 */ 115 w = p/q; 116 t = pio2_hi-(2.0*(s+s*w)-pio2_lo); 117 } else { 118 w = s; 119 __LO(w) = 0; 120 c = (t-w*w)/(s+w); 121 r = p/q; 122 p = 2.0*s*r-(pio2_lo-2.0*c); 123 q = pio4_hi-2.0*w; 124 t = pio4_hi-(p-q); 125 } 126 if(hx>0) return t; else return -t; 127 }