diff options
Diffstat (limited to 'lib/mlibc/options/ansi/musl-generic-math/asin.c')
| -rw-r--r-- | lib/mlibc/options/ansi/musl-generic-math/asin.c | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/lib/mlibc/options/ansi/musl-generic-math/asin.c b/lib/mlibc/options/ansi/musl-generic-math/asin.c new file mode 100644 index 0000000..c926b18 --- /dev/null +++ b/lib/mlibc/options/ansi/musl-generic-math/asin.c @@ -0,0 +1,107 @@ +/* origin: FreeBSD /usr/src/lib/msun/src/e_asin.c */ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunSoft, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ +/* asin(x) + * Method : + * Since asin(x) = x + x^3/6 + x^5*3/40 + x^7*15/336 + ... + * we approximate asin(x) on [0,0.5] by + * asin(x) = x + x*x^2*R(x^2) + * where + * R(x^2) is a rational approximation of (asin(x)-x)/x^3 + * and its remez error is bounded by + * |(asin(x)-x)/x^3 - R(x^2)| < 2^(-58.75) + * + * For x in [0.5,1] + * asin(x) = pi/2-2*asin(sqrt((1-x)/2)) + * Let y = (1-x), z = y/2, s := sqrt(z), and pio2_hi+pio2_lo=pi/2; + * then for x>0.98 + * asin(x) = pi/2 - 2*(s+s*z*R(z)) + * = pio2_hi - (2*(s+s*z*R(z)) - pio2_lo) + * For x<=0.98, let pio4_hi = pio2_hi/2, then + * f = hi part of s; + * c = sqrt(z) - f = (z-f*f)/(s+f) ...f+c=sqrt(z) + * and + * asin(x) = pi/2 - 2*(s+s*z*R(z)) + * = pio4_hi+(pio4-2s)-(2s*z*R(z)-pio2_lo) + * = pio4_hi+(pio4-2f)-(2s*z*R(z)-(pio2_lo+2c)) + * + * Special cases: + * if x is NaN, return x itself; + * if |x|>1, return NaN with invalid signal. + * + */ + +#include "libm.h" + +static const double +pio2_hi = 1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */ +pio2_lo = 6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */ +/* coefficients for R(x^2) */ +pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */ +pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */ +pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */ +pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */ +pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */ +pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */ +qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */ +qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */ +qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */ +qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */ + +static double R(double z) +{ + double_t p, q; + p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*pS5))))); + q = 1.0+z*(qS1+z*(qS2+z*(qS3+z*qS4))); + return p/q; +} + +double asin(double x) +{ + double z,r,s; + uint32_t hx,ix; + + GET_HIGH_WORD(hx, x); + ix = hx & 0x7fffffff; + /* |x| >= 1 or nan */ + if (ix >= 0x3ff00000) { + uint32_t lx; + GET_LOW_WORD(lx, x); + if ((ix-0x3ff00000 | lx) == 0) + /* asin(1) = +-pi/2 with inexact */ + return x*pio2_hi + 0x1p-120f; + return 0/(x-x); + } + /* |x| < 0.5 */ + if (ix < 0x3fe00000) { + /* if 0x1p-1022 <= |x| < 0x1p-26, avoid raising underflow */ + if (ix < 0x3e500000 && ix >= 0x00100000) + return x; + return x + x*R(x*x); + } + /* 1 > |x| >= 0.5 */ + z = (1 - fabs(x))*0.5; + s = sqrt(z); + r = R(z); + if (ix >= 0x3fef3333) { /* if |x| > 0.975 */ + x = pio2_hi-(2*(s+s*r)-pio2_lo); + } else { + double f,c; + /* f+c = sqrt(z) */ + f = s; + SET_LOW_WORD(f,0); + c = (z-f*f)/(s+f); + x = 0.5*pio2_hi - (2*s*r - (pio2_lo-2*c) - (0.5*pio2_hi-2*f)); + } + if (hx >> 31) + return -x; + return x; +} |