vendor/libm-0.1.4/src/math/asinf.rs

   1 /* origin: FreeBSD /usr/src/lib/msun/src/e_asinf.c */
   2 /*
   3  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   4  */
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 use super::fabsf::fabsf;
  17 use super::sqrt::sqrt;
  18
  19 const PIO2: f64 = 1.570796326794896558e+00;
  20
  21 /* coefficients for R(x^2) */
  22 const P_S0: f32 = 1.6666586697e-01;
  23 const P_S1: f32 = -4.2743422091e-02;
  24 const P_S2: f32 = -8.6563630030e-03;
  25 const Q_S1: f32 = -7.0662963390e-01;
  26
  27 #[inline]
  28 fn r(z: f32) -> f32 {
  29     let p = z * (P_S0 + z * (P_S1 + z * P_S2));
  30     let q = 1. + z * Q_S1;
  31     p / q
  32 }
  33
  34 /// Arcsine (f32)
  35 ///
  36 /// Computes the inverse sine (arc sine) of the argument `x`.
  37 /// Arguments to asin must be in the range -1 to 1.
  38 /// Returns values in radians, in the range of -pi/2 to pi/2.
  39 #[inline]
  40 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
  41 pub fn asinf(mut x: f32) -> f32 {
  42     let x1p_120 = f64::from_bits(0x3870000000000000); // 0x1p-120 === 2 ^ (-120)
  43
  44     let hx = x.to_bits();
  45     let ix = hx & 0x7fffffff;
  46
  47     if ix >= 0x3f800000 {
  48         /* |x| >= 1 */
  49         if ix == 0x3f800000 {
  50             /* |x| == 1 */
  51             return ((x as f64) * PIO2 + x1p_120) as f32; /* asin(+-1) = +-pi/2 with inexact */
  52         }
  53         return 0. / (x - x); /* asin(|x|>1) is NaN */
  54     }
  55
  56     if ix < 0x3f000000 {
  57         /* |x| < 0.5 */
  58         /* if 0x1p-126 <= |x| < 0x1p-12, avoid raising underflow */
  59         if (ix < 0x39800000) && (ix >= 0x00800000) {
  60             return x;
  61         }
  62         return x + x * r(x * x);
  63     }
  64
  65     /* 1 > |x| >= 0.5 */
  66     let z = (1. - fabsf(x)) * 0.5;
  67     let s = sqrt(z as f64);
  68     x = (PIO2 - 2. * (s + s * (r(z) as f64))) as f32;
  69     if (hx >> 31) != 0 {
  70         -x
  71     } else {
  72         x
  73     }
  74 }