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Diffstat (limited to 'vendor/libm/src/math/asin.rs')
| -rw-r--r-- | vendor/libm/src/math/asin.rs | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/vendor/libm/src/math/asin.rs b/vendor/libm/src/math/asin.rs new file mode 100644 index 000000000..774475e51 --- /dev/null +++ b/vendor/libm/src/math/asin.rs @@ -0,0 +1,121 @@ +/* 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. + * + */ + +use super::{fabs, get_high_word, get_low_word, sqrt, with_set_low_word}; + +const PIO2_HI: f64 = 1.57079632679489655800e+00; /* 0x3FF921FB, 0x54442D18 */ +const PIO2_LO: f64 = 6.12323399573676603587e-17; /* 0x3C91A626, 0x33145C07 */ +/* coefficients for R(x^2) */ +const P_S0: f64 = 1.66666666666666657415e-01; /* 0x3FC55555, 0x55555555 */ +const P_S1: f64 = -3.25565818622400915405e-01; /* 0xBFD4D612, 0x03EB6F7D */ +const P_S2: f64 = 2.01212532134862925881e-01; /* 0x3FC9C155, 0x0E884455 */ +const P_S3: f64 = -4.00555345006794114027e-02; /* 0xBFA48228, 0xB5688F3B */ +const P_S4: f64 = 7.91534994289814532176e-04; /* 0x3F49EFE0, 0x7501B288 */ +const P_S5: f64 = 3.47933107596021167570e-05; /* 0x3F023DE1, 0x0DFDF709 */ +const Q_S1: f64 = -2.40339491173441421878e+00; /* 0xC0033A27, 0x1C8A2D4B */ +const Q_S2: f64 = 2.02094576023350569471e+00; /* 0x40002AE5, 0x9C598AC8 */ +const Q_S3: f64 = -6.88283971605453293030e-01; /* 0xBFE6066C, 0x1B8D0159 */ +const Q_S4: f64 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */ + +#[inline] +fn comp_r(z: f64) -> f64 { + let p = z * (P_S0 + z * (P_S1 + z * (P_S2 + z * (P_S3 + z * (P_S4 + z * P_S5))))); + let q = 1.0 + z * (Q_S1 + z * (Q_S2 + z * (Q_S3 + z * Q_S4))); + p / q +} + +/// Arcsine (f64) +/// +/// Computes the inverse sine (arc sine) of the argument `x`. +/// Arguments to asin must be in the range -1 to 1. +/// Returns values in radians, in the range of -pi/2 to pi/2. +#[inline] +#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] +pub fn asin(mut x: f64) -> f64 { + let z: f64; + let r: f64; + let s: f64; + let hx: u32; + let ix: u32; + + hx = get_high_word(x); + ix = hx & 0x7fffffff; + /* |x| >= 1 or nan */ + if ix >= 0x3ff00000 { + let lx: u32; + lx = get_low_word(x); + if ((ix - 0x3ff00000) | lx) == 0 { + /* asin(1) = +-pi/2 with inexact */ + return x * PIO2_HI + f64::from_bits(0x3870000000000000); + } else { + return 0.0 / (x - x); + } + } + /* |x| < 0.5 */ + if ix < 0x3fe00000 { + /* if 0x1p-1022 <= |x| < 0x1p-26, avoid raising underflow */ + if ix < 0x3e500000 && ix >= 0x00100000 { + return x; + } else { + return x + x * comp_r(x * x); + } + } + /* 1 > |x| >= 0.5 */ + z = (1.0 - fabs(x)) * 0.5; + s = sqrt(z); + r = comp_r(z); + if ix >= 0x3fef3333 { + /* if |x| > 0.975 */ + x = PIO2_HI - (2. * (s + s * r) - PIO2_LO); + } else { + let f: f64; + let c: f64; + /* f+c = sqrt(z) */ + f = with_set_low_word(s, 0); + c = (z - f * f) / (s + f); + x = 0.5 * PIO2_HI - (2.0 * s * r - (PIO2_LO - 2.0 * c) - (0.5 * PIO2_HI - 2.0 * f)); + } + if hx >> 31 != 0 { + -x + } else { + x + } +} |