2 /* @(#)e_asin.c 1.3 95/01/18 */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
11 * ====================================================
16 * Since asin(x) = x + x^3/6 + x^5*3/40 + x^7*15/336 + ...
17 * we approximate asin(x) on [0,0.5] by
18 * asin(x) = x + x*x^2*R(x^2)
20 * R(x^2) is a rational approximation of (asin(x)-x)/x^3
21 * and its remez error is bounded by
22 * |(asin(x)-x)/x^3 - R(x^2)| < 2^(-58.75)
25 * asin(x) = pi/2-2*asin(sqrt((1-x)/2))
26 * Let y = (1-x), z = y/2, s := sqrt(z), and pio2_hi+pio2_lo=pi/2;
28 * asin(x) = pi/2 - 2*(s+s*z*R(z))
29 * = pio2_hi - (2*(s+s*z*R(z)) - pio2_lo)
30 * For x<=0.98, let pio4_hi = pio2_hi/2, then
32 * c = sqrt(z) - f = (z-f*f)/(s+f) ...f+c=sqrt(z)
34 * asin(x) = pi/2 - 2*(s+s*z*R(z))
35 * = pio4_hi+(pio4-2s)-(2s*z*R(z)-pio2_lo)
36 * = pio4_hi+(pio4-2f)-(2s*z*R(z)-(pio2_lo+2c))
39 * if x is NaN, return x itself;
40 * if |x|>1, return NaN with invalid signal.
46 #include "math_private.h"
49 one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
51 pio2_hi = 1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */
52 pio2_lo = 6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */
53 pio4_hi = 7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */
54 /* coefficient for R(x^2) */
55 pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */
56 pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */
57 pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */
58 pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */
59 pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */
60 pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */
61 qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */
62 qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */
63 qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */
64 qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */
69 double t=0.0,w,p,q,c,r,s;
73 if(ix>= 0x3ff00000) { /* |x|>= 1 */
76 if(((ix-0x3ff00000)|lx)==0)
77 /* asin(1)=+-pi/2 with inexact */
78 return x*pio2_hi+x*pio2_lo;
79 return (x-x)/(x-x); /* asin(|x|>1) is NaN */
80 } else if (ix<0x3fe00000) { /* |x|<0.5 */
81 if(ix<0x3e400000) { /* if |x| < 2**-27 */
82 if(huge+x>one) return x;/* return x with inexact if x!=0*/
85 p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5)))));
86 q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4)));
93 p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5)))));
94 q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4)));
96 if(ix>=0x3FEF3333) { /* if |x| > 0.975 */
98 t = pio2_hi-(2.0*(s+s*w)-pio2_lo);
104 p = 2.0*s*r-(pio2_lo-2.0*c);
108 if(hx>0) return t; else return -t;