/* origin: FreeBSD /usr/src/lib/msun/src/e_logf.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.

 * ====================================================

 */

const LN2_HI: f32 = 6.9313812256e-01; /* 0x3f317180 */

const LN2_LO: f32 = 9.0580006145e-06; /* 0x3717f7d1 */

/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */

const LG1: f32 = 0.66666662693; /*  0xaaaaaa.0p-24*/

const LG2: f32 = 0.40000972152; /*  0xccce13.0p-25 */

const LG3: f32 = 0.28498786688; /*  0x91e9ee.0p-25 */

const LG4: f32 = 0.24279078841; /*  0xf89e26.0p-26 */

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

pub fn logf(mut x: f32) -> f32 {

    let x1p25 = f32::from_bits(0x4c000000); // 0x1p25f === 2 ^ 25

    let mut ix = x.to_bits();

    let mut k = 0i32;

    if (ix < 0x00800000) || ((ix >> 31) != 0) {

        /* x < 2**-126  */

        if ix << 1 == 0 {

            return -1. / (x * x); /* log(+-0)=-inf */

        }

        if (ix >> 31) != 0 {

            return (x - x) / 0.; /* log(-#) = NaN */

        }

        /* subnormal number, scale up x */

        k -= 25;

        x *= x1p25;

        ix = x.to_bits();

    } else if ix >= 0x7f800000 {

        return x;

    } else if ix == 0x3f800000 {

        return 0.;

    }

    /* reduce x into [sqrt(2)/2, sqrt(2)] */

    ix += 0x3f800000 - 0x3f3504f3;

    k += ((ix >> 23) as i32) - 0x7f;

    ix = (ix & 0x007fffff) + 0x3f3504f3;

    x = f32::from_bits(ix);

    let f = x - 1.;

    let s = f / (2. + f);

    let z = s * s;

    let w = z * z;

    let t1 = w * (LG2 + w * LG4);

    let t2 = z * (LG1 + w * LG3);

    let r = t2 + t1;

    let hfsq = 0.5 * f * f;

    let dk = k as f32;

    s * (hfsq + r) + dk * LN2_LO - hfsq + f + dk * LN2_HI

}