e_asin.cpp (3580B)
1 /* @(#)e_asin.c 1.3 95/01/18 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunSoft, 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 //#include <sys/cdefs.h> 14 //__FBSDID("$FreeBSD$"); 15 16 /* __ieee754_asin(x) 17 * Method : 18 * Since asin(x) = x + x^3/6 + x^5*3/40 + x^7*15/336 + ... 19 * we approximate asin(x) on [0,0.5] by 20 * asin(x) = x + x*x^2*R(x^2) 21 * where 22 * R(x^2) is a rational approximation of (asin(x)-x)/x^3 23 * and its remez error is bounded by 24 * |(asin(x)-x)/x^3 - R(x^2)| < 2^(-58.75) 25 * 26 * For x in [0.5,1] 27 * asin(x) = pi/2-2*asin(sqrt((1-x)/2)) 28 * Let y = (1-x), z = y/2, s := sqrt(z), and pio2_hi+pio2_lo=pi/2; 29 * then for x>0.98 30 * asin(x) = pi/2 - 2*(s+s*z*R(z)) 31 * = pio2_hi - (2*(s+s*z*R(z)) - pio2_lo) 32 * For x<=0.98, let pio4_hi = pio2_hi/2, then 33 * f = hi part of s; 34 * c = sqrt(z) - f = (z-f*f)/(s+f) ...f+c=sqrt(z) 35 * and 36 * asin(x) = pi/2 - 2*(s+s*z*R(z)) 37 * = pio4_hi+(pio4-2s)-(2s*z*R(z)-pio2_lo) 38 * = pio4_hi+(pio4-2f)-(2s*z*R(z)-(pio2_lo+2c)) 39 * 40 * Special cases: 41 * if x is NaN, return x itself; 42 * if |x|>1, return NaN with invalid signal. 43 * 44 */ 45 46 #include <float.h> 47 #include <math.h> 48 49 #include "math_private.h" 50 51 static const double 52 one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */ 53 huge = 1.000e+300, 54 pio2_hi = 1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */ 55 pio2_lo = 6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */ 56 pio4_hi = 7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */ 57 /* coefficient for R(x^2) */ 58 pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */ 59 pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */ 60 pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */ 61 pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */ 62 pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */ 63 pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */ 64 qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */ 65 qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */ 66 qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */ 67 qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */ 68 69 double 70 __ieee754_asin(double x) 71 { 72 double t=0.0,w,p,q,c,r,s; 73 int32_t hx,ix; 74 GET_HIGH_WORD(hx,x); 75 ix = hx&0x7fffffff; 76 if(ix>= 0x3ff00000) { /* |x|>= 1 */ 77 u_int32_t lx; 78 GET_LOW_WORD(lx,x); 79 if(((ix-0x3ff00000)|lx)==0) 80 /* asin(1)=+-pi/2 with inexact */ 81 return x*pio2_hi+x*pio2_lo; 82 return (x-x)/(x-x); /* asin(|x|>1) is NaN */ 83 } else if (ix<0x3fe00000) { /* |x|<0.5 */ 84 if(ix<0x3e500000) { /* if |x| < 2**-26 */ 85 if(huge+x>one) return x;/* return x with inexact if x!=0*/ 86 } 87 t = x*x; 88 p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5))))); 89 q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4))); 90 w = p/q; 91 return x+x*w; 92 } 93 /* 1> |x|>= 0.5 */ 94 w = one-fabs(x); 95 t = w*0.5; 96 p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5))))); 97 q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4))); 98 s = sqrt(t); 99 if(ix>=0x3FEF3333) { /* if |x| > 0.975 */ 100 w = p/q; 101 t = pio2_hi-(2.0*(s+s*w)-pio2_lo); 102 } else { 103 w = s; 104 SET_LOW_WORD(w,0); 105 c = (t-w*w)/(s+w); 106 r = p/q; 107 p = 2.0*s*r-(pio2_lo-2.0*c); 108 q = pio4_hi-2.0*w; 109 t = pio4_hi-(p-q); 110 } 111 if(hx>0) return t; else return -t; 112 }