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/* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
/*
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
*/
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
use super::sqrtf::sqrtf;
const PIO2_HI: f32 = 1.5707962513e+00; /* 0x3fc90fda */
const PIO2_LO: f32 = 7.5497894159e-08; /* 0x33a22168 */
const P_S0: f32 = 1.6666586697e-01;
const P_S1: f32 = -4.2743422091e-02;
const P_S2: f32 = -8.6563630030e-03;
const Q_S1: f32 = -7.0662963390e-01;
fn r(z: f32) -> f32 {
let p = z * (P_S0 + z * (P_S1 + z * P_S2));
let q = 1. + z * Q_S1;
p / q
}
/// Arccosine (f32)
///
/// Computes the inverse cosine (arc cosine) of the input value.
/// Arguments must be in the range -1 to 1.
/// Returns values in radians, in the range of 0 to pi.
#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
pub fn acosf(x: f32) -> f32 {
let x1p_120 = f32::from_bits(0x03800000); // 0x1p-120 === 2 ^ (-120)
let z: f32;
let w: f32;
let s: f32;
let mut hx = x.to_bits();
let ix = hx & 0x7fffffff;
/* |x| >= 1 or nan */
if ix >= 0x3f800000 {
if ix == 0x3f800000 {
if (hx >> 31) != 0 {
return 2. * PIO2_HI + x1p_120;
}
return 0.;
}
return 0. / (x - x);
}
/* |x| < 0.5 */
if ix < 0x3f000000 {
if ix <= 0x32800000 {
/* |x| < 2**-26 */
return PIO2_HI + x1p_120;
}
return PIO2_HI - (x - (PIO2_LO - x * r(x * x)));
}
/* x < -0.5 */
if (hx >> 31) != 0 {
z = (1. + x) * 0.5;
s = sqrtf(z);
w = r(z) * s - PIO2_LO;
return 2. * (PIO2_HI - (s + w));
}
/* x > 0.5 */
z = (1. - x) * 0.5;
s = sqrtf(z);
hx = s.to_bits();
let df = f32::from_bits(hx & 0xfffff000);
let c = (z - df * df) / (s + df);
w = r(z) * s + c;
2. * (df + w)
}