/* origin: FreeBSD /usr/src/lib/msun/src/e_powf.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::{fabsf, scalbnf, sqrtf};

const BP: [f32; 2] = [1.0, 1.5];

const DP_H: [f32; 2] = [0.0, 5.84960938e-01]; /* 0x3f15c000 */

const DP_L: [f32; 2] = [0.0, 1.56322085e-06]; /* 0x35d1cfdc */

const TWO24: f32 = 16777216.0; /* 0x4b800000 */

const HUGE: f32 = 1.0e30;

const TINY: f32 = 1.0e-30;

const L1: f32 = 6.0000002384e-01; /* 0x3f19999a */

const L2: f32 = 4.2857143283e-01; /* 0x3edb6db7 */

const L3: f32 = 3.3333334327e-01; /* 0x3eaaaaab */

const L4: f32 = 2.7272811532e-01; /* 0x3e8ba305 */

const L5: f32 = 2.3066075146e-01; /* 0x3e6c3255 */

const L6: f32 = 2.0697501302e-01; /* 0x3e53f142 */

const P1: f32 = 1.6666667163e-01; /* 0x3e2aaaab */

const P2: f32 = -2.7777778450e-03; /* 0xbb360b61 */

const P3: f32 = 6.6137559770e-05; /* 0x388ab355 */

const P4: f32 = -1.6533901999e-06; /* 0xb5ddea0e */

const P5: f32 = 4.1381369442e-08; /* 0x3331bb4c */

const LG2: f32 = 6.9314718246e-01; /* 0x3f317218 */

const LG2_H: f32 = 6.93145752e-01; /* 0x3f317200 */

const LG2_L: f32 = 1.42860654e-06; /* 0x35bfbe8c */

const OVT: f32 = 4.2995665694e-08; /* -(128-log2(ovfl+.5ulp)) */

const CP: f32 = 9.6179670095e-01; /* 0x3f76384f =2/(3ln2) */

const CP_H: f32 = 9.6191406250e-01; /* 0x3f764000 =12b cp */

const CP_L: f32 = -1.1736857402e-04; /* 0xb8f623c6 =tail of cp_h */

const IVLN2: f32 = 1.4426950216e+00;

const IVLN2_H: f32 = 1.4426879883e+00;

const IVLN2_L: f32 = 7.0526075433e-06;

/// Returns `x` to the power of `y` (f32).

#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]

pub fn powf(x: f32, y: f32) -> f32 {

    let mut z: f32;

    let mut ax: f32;

    let z_h: f32;

    let z_l: f32;

    let mut p_h: f32;

    let mut p_l: f32;

    let y1: f32;

    let mut t1: f32;

    let t2: f32;

    let mut r: f32;

    let s: f32;

    let mut sn: f32;

    let mut t: f32;

    let mut u: f32;

    let mut v: f32;

    let mut w: f32;

    let i: i32;

    let mut j: i32;

    let mut k: i32;

    let mut yisint: i32;

    let mut n: i32;

    let hx: i32;

    let hy: i32;

    let mut ix: i32;

    let iy: i32;

    let mut is: i32;

    hx = x.to_bits() as i32;

    hy = y.to_bits() as i32;

    ix = hx & 0x7fffffff;

    iy = hy & 0x7fffffff;

    /* x**0 = 1, even if x is NaN */

    if iy == 0 {

        return 1.0;

    }

    /* 1**y = 1, even if y is NaN */

    if hx == 0x3f800000 {

        return 1.0;

    }

    /* NaN if either arg is NaN */

    if ix > 0x7f800000 || iy > 0x7f800000 {

        return x + y;

    }

    /* determine if y is an odd int when x < 0

     * yisint = 0       ... y is not an integer

     * yisint = 1       ... y is an odd int

     * yisint = 2       ... y is an even int

     */

    yisint = 0;

    if hx < 0 {

        if iy >= 0x4b800000 {

            yisint = 2; /* even integer y */

        } else if iy >= 0x3f800000 {

            k = (iy >> 23) - 0x7f; /* exponent */

            j = iy >> (23 - k);

            if (j << (23 - k)) == iy {

                yisint = 2 - (j & 1);

            }

        }

    }

    /* special value of y */

    if iy == 0x7f800000 {

        /* y is +-inf */

        if ix == 0x3f800000 {

            /* (-1)**+-inf is 1 */

            return 1.0;

        } else if ix > 0x3f800000 {

            /* (|x|>1)**+-inf = inf,0 */

            return if hy >= 0 { y } else { 0.0 };

        } else {

            /* (|x|<1)**+-inf = 0,inf */

            return if hy >= 0 { 0.0 } else { -y };

        }

    }

    if iy == 0x3f800000 {

        /* y is +-1 */

        return if hy >= 0 { x } else { 1.0 / x };

    }

    if hy == 0x40000000 {

        /* y is 2 */

        return x * x;

    }

    if hy == 0x3f000000

       /* y is  0.5 */

       && hx >= 0

    {

        /* x >= +0 */

        return sqrtf(x);

    }

    ax = fabsf(x);

    /* special value of x */

    if ix == 0x7f800000 || ix == 0 || ix == 0x3f800000 {

        /* x is +-0,+-inf,+-1 */

        z = ax;

        if hy < 0 {

            /* z = (1/|x|) */

            z = 1.0 / z;

        }

        if hx < 0 {

            if ((ix - 0x3f800000) | yisint) == 0 {

                z = (z - z) / (z - z); /* (-1)**non-int is NaN */

            } else if yisint == 1 {

                z = -z; /* (x<0)**odd = -(|x|**odd) */

            }

        }

        return z;

    }

    sn = 1.0; /* sign of result */

    if hx < 0 {

        if yisint == 0 {

            /* (x<0)**(non-int) is NaN */

            return (x - x) / (x - x);

        }

        if yisint == 1 {

            /* (x<0)**(odd int) */

            sn = -1.0;

        }

    }

    /* |y| is HUGE */

    if iy > 0x4d000000 {

        /* if |y| > 2**27 */

        /* over/underflow if x is not close to one */

        if ix < 0x3f7ffff8 {

            return if hy < 0 { sn * HUGE * HUGE } else { sn * TINY * TINY };

        }

        if ix > 0x3f800007 {

            return if hy > 0 { sn * HUGE * HUGE } else { sn * TINY * TINY };

        }

        /* now |1-x| is TINY <= 2**-20, suffice to compute

        log(x) by x-x^2/2+x^3/3-x^4/4 */

        t = ax - 1.; /* t has 20 trailing zeros */

        w = (t * t) * (0.5 - t * (0.333333333333 - t * 0.25));

        u = IVLN2_H * t; /* IVLN2_H has 16 sig. bits */

        v = t * IVLN2_L - w * IVLN2;

        t1 = u + v;

        is = t1.to_bits() as i32;

        t1 = f32::from_bits(is as u32 & 0xfffff000);

        t2 = v - (t1 - u);

    } else {

        let mut s2: f32;

        let mut s_h: f32;

        let s_l: f32;

        let mut t_h: f32;

        let mut t_l: f32;

        n = 0;

        /* take care subnormal number */

        if ix < 0x00800000 {

            ax *= TWO24;

            n -= 24;

            ix = ax.to_bits() as i32;

        }

        n += ((ix) >> 23) - 0x7f;

        j = ix & 0x007fffff;

        /* determine interval */

        ix = j | 0x3f800000; /* normalize ix */

        if j <= 0x1cc471 {

            /* |x|<sqrt(3/2) */

            k = 0;

        } else if j < 0x5db3d7 {

            /* |x|<sqrt(3)   */

            k = 1;

        } else {

            k = 0;

            n += 1;

            ix -= 0x00800000;

        }

        ax = f32::from_bits(ix as u32);

        /* compute s = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */

        u = ax - i!(BP, k as usize); /* bp[0]=1.0, bp[1]=1.5 */

        v = 1.0 / (ax + i!(BP, k as usize));

        s = u * v;

        s_h = s;

        is = s_h.to_bits() as i32;

        s_h = f32::from_bits(is as u32 & 0xfffff000);

        /* t_h=ax+bp[k] High */

        is = (((ix as u32 >> 1) & 0xfffff000) | 0x20000000) as i32;

        t_h = f32::from_bits(is as u32 + 0x00400000 + ((k as u32) << 21));

        t_l = ax - (t_h - i!(BP, k as usize));

        s_l = v * ((u - s_h * t_h) - s_h * t_l);

        /* compute log(ax) */

        s2 = s * s;

        r = s2 * s2 * (L1 + s2 * (L2 + s2 * (L3 + s2 * (L4 + s2 * (L5 + s2 * L6)))));

        r += s_l * (s_h + s);

        s2 = s_h * s_h;

        t_h = 3.0 + s2 + r;

        is = t_h.to_bits() as i32;

        t_h = f32::from_bits(is as u32 & 0xfffff000);

        t_l = r - ((t_h - 3.0) - s2);

        /* u+v = s*(1+...) */

        u = s_h * t_h;

        v = s_l * t_h + t_l * s;

        /* 2/(3log2)*(s+...) */

        p_h = u + v;

        is = p_h.to_bits() as i32;

        p_h = f32::from_bits(is as u32 & 0xfffff000);

        p_l = v - (p_h - u);

        z_h = CP_H * p_h; /* cp_h+cp_l = 2/(3*log2) */

        z_l = CP_L * p_h + p_l * CP + i!(DP_L, k as usize);

        /* log2(ax) = (s+..)*2/(3*log2) = n + dp_h + z_h + z_l */

        t = n as f32;

        t1 = ((z_h + z_l) + i!(DP_H, k as usize)) + t;

        is = t1.to_bits() as i32;

        t1 = f32::from_bits(is as u32 & 0xfffff000);

        t2 = z_l - (((t1 - t) - i!(DP_H, k as usize)) - z_h);

    };

    /* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */

    is = y.to_bits() as i32;

    y1 = f32::from_bits(is as u32 & 0xfffff000);

    p_l = (y - y1) * t1 + y * t2;

    p_h = y1 * t1;

    z = p_l + p_h;

    j = z.to_bits() as i32;

    if j > 0x43000000 {

        /* if z > 128 */

        return sn * HUGE * HUGE; /* overflow */

    } else if j == 0x43000000 {

        /* if z == 128 */

        if p_l + OVT > z - p_h {

            return sn * HUGE * HUGE; /* overflow */

        }

    } else if (j & 0x7fffffff) > 0x43160000 {

        /* z < -150 */

        // FIXME: check should be  (uint32_t)j > 0xc3160000

        return sn * TINY * TINY; /* underflow */

    } else if j as u32 == 0xc3160000

              /* z == -150 */

              && p_l <= z - p_h

    {

        return sn * TINY * TINY; /* underflow */

    }

    /*

     * compute 2**(p_h+p_l)

     */

    i = j & 0x7fffffff;

    k = (i >> 23) - 0x7f;

    n = 0;

    if i > 0x3f000000 {

        /* if |z| > 0.5, set n = [z+0.5] */

        n = j + (0x00800000 >> (k + 1));

        k = ((n & 0x7fffffff) >> 23) - 0x7f; /* new k for n */

        t = f32::from_bits(n as u32 & !(0x007fffff >> k));

        n = ((n & 0x007fffff) | 0x00800000) >> (23 - k);

        if j < 0 {

            n = -n;

        }

        p_h -= t;

    }

    t = p_l + p_h;

    is = t.to_bits() as i32;

    t = f32::from_bits(is as u32 & 0xffff8000);

    u = t * LG2_H;

    v = (p_l - (t - p_h)) * LG2 + t * LG2_L;

    z = u + v;

    w = v - (z - u);

    t = z * z;

    t1 = z - t * (P1 + t * (P2 + t * (P3 + t * (P4 + t * P5))));

    r = (z * t1) / (t1 - 2.0) - (w + z * w);

    z = 1.0 - (r - z);

    j = z.to_bits() as i32;

    j += n << 23;

    if (j >> 23) <= 0 {

        /* subnormal output */

        z = scalbnf(z, n);

    } else {

        z = f32::from_bits(j as u32);

    }

    sn * z

}