1 /* origin: FreeBSD /usr/src/lib/msun/src/e_acos.c */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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
10 * ====================================================
14 * acos(x) = pi/2 - asin(x)
15 * acos(-x) = pi/2 + asin(x)
17 * acos(x) = pi/2 - (x + x*x^2*R(x^2)) (see asin.c)
19 * acos(x) = pi/2 - (pi/2 - 2asin(sqrt((1-x)/2)))
20 * = 2asin(sqrt((1-x)/2))
21 * = 2s + 2s*z*R(z) ...z=(1-x)/2, s=sqrt(z)
22 * = 2f + (2c + 2s*z*R(z))
23 * where f=hi part of s, and c = (z-f*f)/(s+f) is the correction term
24 * for f so that f+c ~ sqrt(z).
26 * acos(x) = pi - 2asin(sqrt((1-|x|)/2))
27 * = pi - 0.5*(s+s*z*R(z)), where z=(1-|x|)/2,s=sqrt(z)
30 * if x is NaN, return x itself;
31 * if |x|>1, return NaN with invalid signal.
33 * Function needed: sqrt
39 one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
40 pi = 3.14159265358979311600e+00, /* 0x400921FB, 0x54442D18 */
41 pio2_hi = 1.57079632679489655800e+00; /* 0x3FF921FB, 0x54442D18 */
42 static const volatile double
43 pio2_lo = 6.12323399573676603587e-17; /* 0x3C91A626, 0x33145C07 */
45 pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */
46 pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */
47 pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */
48 pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */
49 pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */
50 pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */
51 qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */
52 qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */
53 qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */
54 qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */
58 double z,p,q,r,w,s,c,df;
63 if (ix >= 0x3ff00000) { /* |x| >= 1 */
67 if ((ix-0x3ff00000 | lx) == 0) { /* |x|==1 */
68 if (hx > 0) return 0.0; /* acos(1) = 0 */
69 return pi + 2.0*pio2_lo; /* acos(-1)= pi */
71 return (x-x)/(x-x); /* acos(|x|>1) is NaN */
73 if (ix < 0x3fe00000) { /* |x| < 0.5 */
74 if (ix <= 0x3c600000) /* |x| < 2**-57 */
75 return pio2_hi + pio2_lo;
77 p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
78 q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
80 return pio2_hi - (x - (pio2_lo-x*r));
81 } else if (hx < 0) { /* x < -0.5 */
83 p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
84 q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));
88 return pi - 2.0*(s+w);
89 } else { /* x > 0.5 */
95 p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5)))));
96 q = one+z*(qS1+z*(qS2+z*(qS3+z*qS4)));