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/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.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::atanf;
use super::fabsf;
const PI: f32 = 3.1415927410e+00; /* 0x40490fdb */
const PI_LO: f32 = -8.7422776573e-08; /* 0xb3bbbd2e */
/// Arctangent of y/x (f32)
///
/// Computes the inverse tangent (arc tangent) of `y/x`.
/// Produces the correct result even for angles near pi/2 or -pi/2 (that is, when `x` is near 0).
/// Returns a value in radians, in the range of -pi to pi.
#[inline]
#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
pub fn atan2f(y: f32, x: f32) -> f32 {
if x.is_nan() || y.is_nan() {
return x + y;
}
let mut ix = x.to_bits();
let mut iy = y.to_bits();
if ix == 0x3f800000 {
/* x=1.0 */
return atanf(y);
}
let m = ((iy >> 31) & 1) | ((ix >> 30) & 2); /* 2*sign(x)+sign(y) */
ix &= 0x7fffffff;
iy &= 0x7fffffff;
/* when y = 0 */
if iy == 0 {
return match m {
0 | 1 => y, /* atan(+-0,+anything)=+-0 */
2 => PI, /* atan(+0,-anything) = pi */
3 | _ => -PI, /* atan(-0,-anything) =-pi */
};
}
/* when x = 0 */
if ix == 0 {
return if m & 1 != 0 { -PI / 2. } else { PI / 2. };
}
/* when x is INF */
if ix == 0x7f800000 {
return if iy == 0x7f800000 {
match m {
0 => PI / 4., /* atan(+INF,+INF) */
1 => -PI / 4., /* atan(-INF,+INF) */
2 => 3. * PI / 4., /* atan(+INF,-INF)*/
3 | _ => -3. * PI / 4., /* atan(-INF,-INF)*/
}
} else {
match m {
0 => 0., /* atan(+...,+INF) */
1 => -0., /* atan(-...,+INF) */
2 => PI, /* atan(+...,-INF) */
3 | _ => -PI, /* atan(-...,-INF) */
}
};
}
/* |y/x| > 0x1p26 */
if (ix + (26 << 23) < iy) || (iy == 0x7f800000) {
return if m & 1 != 0 { -PI / 2. } else { PI / 2. };
}
/* z = atan(|y/x|) with correct underflow */
let z = if (m & 2 != 0) && (iy + (26 << 23) < ix) {
/*|y/x| < 0x1p-26, x < 0 */
0.
} else {
atanf(fabsf(y / x))
};
match m {
0 => z, /* atan(+,+) */
1 => -z, /* atan(-,+) */
2 => PI - (z - PI_LO), /* atan(+,-) */
_ => (z - PI_LO) - PI, /* case 3 */ /* atan(-,-) */
}
}
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