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    use super::{log1pf, logf, sqrtf};

    const LN2: f32 = 0.693147180559945309417232121458176568;

    /// Inverse hyperbolic cosine (f32)
    ///
    /// Calculates the inverse hyperbolic cosine of `x`.
    /// Is defined as `log(x + sqrt(x*x-1))`.
    /// `x` must be a number greater than or equal to 1.
    pub fn acoshf(x: f32) -> f32 {
        let u = x.to_bits();
        let a = u & 0x7fffffff;

        if a < 0x3f800000 + (1 << 23) {
            /* |x| < 2, invalid if x < 1 or nan */
            /* up to 2ulp error in [1,1.125] */
            return log1pf(x - 1.0 + sqrtf((x - 1.0) * (x - 1.0) + 2.0 * (x - 1.0)));
        }
        if a < 0x3f800000 + (12 << 23) {
            /* |x| < 0x1p12 */
            return logf(2.0 * x - 1.0 / (x + sqrtf(x * x - 1.0)));
        }
        /* x >= 0x1p12 */
        return logf(x) + LN2;
    }

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